Is there any example of living beings destroying their environment?

Is there any example of living beings destroying their environment?

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I had an argument with someone about mankind being the only being destroying its own environment. I don't think this is true, yet, I cannot provide any example of significant importance.

Are there any examples of a living being destroying its own environment, making it uninhabitable to them? (Bonus point if this event led to an environmental catastrophe or to their extinction.)

Species don't live in isolation

As simple as the question seems, it actually contains some issue in the conceptualization of a species in isolation that affect or does not affect its environment.

Species do not exist in isolation from others. Many species have very important impact on their environment. These transformations would yield the environment to be unsuitable for the survival of the species over time if there were no other species to interact with. But by the existence of other species creating a cycle of, say oxygen for example, the transformation that the species is bringing to their environment is not seen as destroying the environment. In fact, if they were to disappear that could be an important problem. Let's go through examples

Example 1: Cyanobacteria and the Great Oxygenation Event

In the history of our planet, about 2.45 billions years ago, some species started to produce oxygen. Before that the oxygen level on earth was very low. We refer to this rise in oxygen as the Great Oxygenation Event. At the time, there was very few species that were performing respiration (breaking up oxygen and producing carbonic gas). Oxygen is a very reactive molecule and the rise in oxygen level was actually a MASSIVE environmental impact (arguably the most important life-induced environmental that had ever happen on Earth). It lead to an event of mass extinction.

The main contributors to this rise in oxygen were cyanobacteria. Cyanobacteria were most definitely destroying their environment. However, today, while modern cyanobaceteria are still producing loads of oxygen, we don't consider they are threatening the environment. In fact, they are fixing quite a bit of carbonic gas, which we rather tend to see as beneficial.

Example 2: Ants

I will not develop this example too much… Ants are greatly affecting forests of the world. Without ants, forests would be pretty different (see this non-peer reviewed source of information).

Ants are typically considered indicator of a "healthy" forest (see Segat et al. 2017; Lawes et al. 2017 and the book Gorb and Gorb 2003). Howe ver ants can also be invasive species that cause massive "destruction" on their habitat (Tsutsui and Suarez 2003; Lach 2003; Ness and Bronstein 2004).

"Destruction" is context specific

So, wether a species is "destroying" it's environment depends upon what other species are around. It also depends upon what you are aiming for (species diversity vs stable communities vs… ) but I won't go into these details.

Instead of asking

What species destroy their environment

it would not be 'more wrong' to ask

What species are present in ecosystem that are not adapted to their presence

or even (although that is a little of a stretch and some may argue on it)

What species have recently been introduced in a new ecosystem? / What species have recently changed their environmental impacts?

Always keep in mind, that no species can live sustainably on its own alone.

Do humans destroy their environment?

What do we mean when we say that humans destroy the environment, then? Human activities have changed drastically very recently. This is caused for two main reasons 1) our technology and, consequently our needs and therefore consumption have changed drastically ever since the industrial era. 2) we went through a demographic explosion.

So, yes we are pumping lots of carbon dioxide in the atmosphere. We get this carbon from forests we cut down, from large carbon reserves that have accumulated over millions of years (petrol, gas, peat and others). This change in our environmental impact is often seen (and for rather good reasons) as destructive.

Other modern species that destroy their own environment

Pretty much any invasive species would qualify as an example of a species that destroys its environment in a way that is not sustainable for itself over the long term. Among the invasive species that have important environmental impact that are seen as highly destructive, I can think of

  • Emerald ash borer (North America)
  • European starling (North America)
  • Feral hogs (North America)
  • Brown tree snake (North America)
  • grey squirrel (North America)
  • Zebra mussel (Europe and North America)
  • Japanese knotweed (Europe)
  • Cane toad (Australia and Latin Amercia)
  • Northern Pacific seastar (Australia)
  • Common wasp (Australia)
  • Rabbits (Australia and New Zealand)
  • Crown-of-thorns starfish (Indo-pacific and Australia)
  • Water hyacinth (global)
  • black wattle (global)
  • Argentine ant (global)

Many of these examples are from western countries because 1) that's what we tend to have most data on 2) because that's what I know having only lived in Europe, North America (and a little bit in Indonesia) 3) There are many examples from Australia and New Zealand because they are the world champions in invasive species and in bad policies concerning these invasive species!

Some readers will probably complain (and some with good reasons) about the species listed as what we mean by "destroy" is very subjective and my list is not intended to show the species that are considered "most destructive". Also, the locations of where these species are invasive might be inaccurate and I welcome anyone to edit them.

You can also consider any predator (incl. herbivores) and parasitic species that is leading it's prey / host to extinction such as

  • The experimental case with lizards in the carribean (Schoener et al. 2001)
  • The atlantic salmons leading shrimps to extinction (with the help of human activities) in the baltic sea
  • The red foxes affecting (with the help of human activities) hares population in Europe.

Coming back to the question

Is there any example of living beings destroying their environment?

Yes… other species than humans are "destroying" their environment. Estimating how much they are destroying their environment is really hard to both define and measure. Without a good working definition and without looking at actual data, I would personally be happy to consider humans as being the species that "destroys" the most today.

Yellowstone National Park ecosystem will serve as a good example of this question.
Here is a link to an youtube video describing the situation pre and post introduction of grey wolves to Yellowstone (around 1940).
As you can infer from the video, when the wolves were hunted to the point they were non-existent in Yellowstone, the herbivores (majorly moose/elk) got free rein of vegetation. Since, they were left unchecked they went on to reduce river bank forest cover by a large margin. If the wolves were not introduced, the larger herbivores would have first driven smaller herbivores to zero by denying them nutrition and later find themselves suffering the same fate once they have completely consumed all vegetation.
However, it can still be argued that we are the only species to consciously destroy our 'habitat'. But the realization that we are doing so is quite recent and maybe, just maybe, if we had known what repercussions our activity would have on our 'habitat' we may not have done so.

What is an example of an organism responding to its environment?

Anything in the environment that causes a change is called a stimulus. Organisms react to many stimuli, including light, temperature, odor, sound, gravity, heat, water, and pressure. The process by which organisms respond to stimuli in ways that keep conditions in their body suitable for life is called homeostasis.

Also Know, what are three examples of a stimulus? Simple examples of stimuli are: When the surface of skin is receiving a pain trigger: heat, breach by object, cold, pressure. When a sensor receives input that causes the organism to 'be aware': Light in the retina, sound/vibration to a hearing organ etc.

In this way, what is an example of a response to stimuli in a living organism?

Light response or phototropism in plants, that is, the bending of the plant towards the sun is the common example of response to a stimuli in an organism. Explanation: A change in the external or internal environment of an organism that can be sensed is called stimulus.

What are 2 main reasons that organisms respond to stimuli?

All living things are able to respond to stimuli in the external environment. For example, living things respond to changes in light, heat, sound, and chemical and mechanical contact. To detect stimuli, organisms have means for receiving information, such as eyes, ears, and taste buds.

Living Things in an Ecosystem

The living creatures in a biological community include microscopic living organisms to all classes and sizes of animals. In a pond, for example, living organisms range in size from the algae and zooplankton in a drop of pond water to the larger fish, amphibians, lilies and cattails that make their homes in the pond. All the different populations of species co-existing and thriving within that same environment define the inhabitants of an ecosystem. The resilience of the community hinges on a cycle -- or chain of events and processes -- that creates food and energy for all the organisms within the community. The ecosystem’s cycle encompasses the producers, consumers and decomposers who cycle energy through the food web so that there is constant productivity, decomposition and nutrient cycling.

1.2: Biology: The Study of Life

In this book, you will learn about one particular branch of science, the branch called biology. Biology is the science of life. OK. That answered the chapter’s question. We’re done.

Just kidding. You knew it couldn’t be THAT short and simple, right?

What exactly is life? What makes something alive? Watch to begin your journey into the study of life.

Characteristics of Life

Look at the duck decoy in Figure below. It looks very similar to a real duck. Of course, real ducks are living things. What about the decoy duck? It looks like a duck, but it is actually made of wood. *Sheesh, did the person who wrote this even LOOK at the picture? I’d say the duck below is probably made from plastic. Ok, back to reading about the wood, plastic, whatever duck:

The decoy duck doesn’t have all the characteristics of a living thing. What characteristics set the real ducks apart from the decoy duck? What are the characteristics of living things?

To be classified as a living thing, an object must have all six of the following characteristics:

  1. It responds to the environment.
  2. It grows and develops.
  3. It produces offspring. – Offspring is just a fancy word for babies or little copies of itself or something like that.
  4. It maintains homeostasis. – Don’t worry, I’ll explain what that means in a minute.
  5. It has complex chemistry.
  6. It consists of cells.

Response to the Environment

All living things detect changes in their environment and respond to them. What happens if you step on a rock? Nothing the rock doesn’t respond because it isn’t alive. “But wait!” you say! “The rock DID move when I stepped on it. Isn’t that responding?” Well, the rock didn’t move by itself. You’re getting into the realm of physics now and not biology: an object tends to stay at rest unless acted upon by an outside force (your foot). Get it? The rock didn’t make a decision to get out of the way. It can’t do that. It’s a rock. We all know rocks aren’t alive. Now, what if you think you are stepping on a rock and actually step on a turtle? The turtle is likely to respond by moving—it may even snap at you!

“Dude! Get off my shell!” That’s what the response means in turtle-speak. The turtle can respond because it’s alive. If you stepped on a dead turtle, well, it wouldn’t move. Therefore, you would hopefully come to the conclusion that this particular turtle isn’t alive, as a response to the environment is one of the characteristics of living things.

Growth and Development

All living things grow and develop. For example, a plant seed may look like a lifeless pebble, but under the right conditions it will grow and develop into a plant. Animals also grow and develop. Look at the animals in Figure below. How will the tadpoles change as they grow and develop into adult frogs?


All living things are capable of reproduction. Reproduction is the process by which living things give rise to offspring. Reproducing may be as simple as a single cell dividing to form two daughter cells. Generally, however, it is much more complicated. Nonetheless, whether a living thing is a huge whale or a microscopic bacterium, it is capable of reproduction.

Keeping Things Constant

All living things are able to maintain a more-or-less constant internal environment. They keep things relatively stable on the inside regardless of the conditions around them. The process of maintaining a stable internal environment is called homeostasis.

Human beings, for example, maintain a stable internal body temperature. If you go outside when the air temperature is below freezing, your body doesn’t freeze. Instead, by shivering and other means, it maintains a stable internal temperature.

Complex Chemistry

All living things—even the simplest life forms—have complex chemistry. Living things consist of large, complex molecules, and they also undergo many complicated chemical changes to stay alive. Complex chemistry is needed to carry out all the functions of life.


All forms of life are built of cells. A cell is the basic unit of the structure and function of living things. Living things may appear very different from one another on the outside, but their cells are very similar. Compare the human cells and onion cells in Figure below. How are they similar?

When you see how complex just a SINGLE cell is, you can better understand how something like that just couldn’t happen by chance.

Symbiosis is a close relationship between organisms of different species in which at least one of the organisms benefits. The other organism may also benefit, or it may be unaffected or harmed by the relationship. Figure below shows an example of symbiosis. The birds in the picture are able to pick out food from the fur of the deer. The deer won’t eat the birds. In fact, the deer knowingly lets the birds rest on it. What, if anything, do you think the deer gets out of the relationship?

Read this article about symbiosis:

Symbiosis: Creatures that Need Each Others

The very idea that a lizard came from a fish, or a human came from an ape-like ancestor is silly. Even millions of years of gradual changes would not cause such a thing. So, even on the face of it, the theory of evolution is untrue. In addition, there are many proofs that show evolution is false. One of those proofs is symbiosis (sim-bee-OH-sus). Symbiosis refers to the relationship between two or more plants or animals of different species that depend on each other to survive. Each provides a necessary service to the other. For example, hummingbirds fly to flowers to get the nectar they need to live, but in the process they collect pollen and take it to other plants so those plants can be pollinated and also live.

Evolutionists try hard (without success) to explain the existence of symbiosis in plant and animal species. They say that species that depend on each other for survival must have “co-evolved.” Darwin talked about his belief that “a flower and a bee might slowly become, either simultaneously or one after the other, modified and adapted in the most perfect manner to each other, by the continued preservation of individuals presenting mutual and slightly favourable deviations of structure.” But this thinking is silly. The “continued preservation of individuals” is what is at stake. Not only could flowers and hummingbirds not have evolved in the first place (since the Law of Biogenesis forbids such), they could not have evolved together. There would be no time for them to do so. If the plant was not pollinated by the hummingbird, the plant would soon die! If the plant’s flower did not provide the hummingbird with nectar, the bird would soon die of starvation—and that would be the end of those species! No time for “evolution”!

In fact, all species of insects, animals, and plants whose lives depend on other creatures would have only a matter of days, weeks, or months at the most before they would die. No organism could have survived for millions of years as it waited for “gradual changes” to occur so that the symbiosis relationship could “slowly become” workable. Both parties in a symbiotic relationship would have to be in existence together, each fully operational and doing its job, for both to survive.

Consider, for example, the Oceanic Whitetip Shark—a competitive, fearless predator that does not avoid trouble in favor of an easier meal. Famed oceanographer Jacques Cousteau described the Oceanic Whitetip as “the most dangerous of all sharks.” This shark feeds on bony fishes including lancetfish, oarfish, barracuda, jacks, dolphinfish, marlin, tuna, mackerels—and even garbage. If other species of sharks are encountered, the Whitetip becomes aggressive and dominates over them. It will bite into schools of bony fishes, and swim through schools of feeding tuna with wide-open jaws, scooping up the tuna as they unknowingly swim into the shark’s mouth.

Of course, consuming all those smaller fish causes bits of food and parasites to collect around their teeth. Food particles can produce disease or a build-up of matter that can hinder eating. So God created this ferocious predator to allow Pilotfish to swim into its mouth to clean away food particles from between its teeth! God created the Pilotfish to act as a biological toothbrush! The shark is relieved of painful parasites and the Pilotfish gains protection by getting to hang around a fierce predator. Their symbiotic relationship is proof of God!

Another amazing example of symbiosis involving completely different species of sea life is the “Watchman Goby” and the shrimp. The shrimp digs and maintains a burrow in the sand for itself and the fish to live in. The constantly moving ocean water continually shifts the sand around and would fill up the burrow if not for the relentless efforts of the shrimp. In the meantime, the Goby keeps watch for danger, and actually warns the almost blind shrimp of possible predators. The shrimp uses its antennae to keep in contact with the fish, and the Goby flicks the shrimp with its tail when alarmed by a possible threat. Both benefit from this amazing symbiotic relationship: the shrimp gets a warning of approaching danger, and the goby gets a safe home and a place to lay its eggs.

Symbiosis is proof of God—and proof that evolution is a myth. God designed hundreds of thousands of His living organisms to speak to humans—if we will listen—that the Creator exists. Indeed, “There is no speech nor language where their voice is not heard” (Psalm 19:3).

Copyright © 2010 Apologetics Press, Inc. All rights reserved.

Want to read some more Christian articles about symbiosis? Check out these urls for some great proofs that God created our world:

Ant Farmers and their Aphids

Yahweh, Yuccas, and a Young Earth

This video shows cleaner fish and cleaner shrimp cleaning other marine animals much like the symbiosis discussed above between the shark and pilot fish. Notice the trust the shrimp shows as it climbs right into the eel’s mouth.

Competition is a relationship between living things that depend on the same resources. The resources may be food, water, or anything else they both need. Competition occurs whenever they both try to get the same resources in the same place and at the same time. You know, like when you and your sister both try to get the leftover hamburger from last night’s dinner AT THE SAME TIME… There’s going to be a bit of competition.

Levels of Organization

The living world can be organized into different levels. For example, many individual organisms can be organized into the following levels:

  • Cell: basic unit of all living things
  • Tissue: a white thing to blow your nose on…OOPS, I mean…a group of cells of the same kind
  • Organ: something you play music on – JUST KIDDING (at least in this context)! It’s actually a structure composed of one or more types of tissues.
  • Organ system: group of organs that work together to do a certain job
  • Organism: individual living thing that may be made up of one or more organ systems – like, you know, an animal, plant, creature, or single-celled life-form

Examples of these levels of organization are shown in Figure below.

There are also levels of organization above the individual organism. These levels are illustrated in Figure below.

  • Organisms of the same species that live in the same area make up a population. For example, all of the goldfish living in the same area make up a goldfish population.
  • All of the populations that live in the same area make up a community. The community that includes the goldfish population also includes the populations of other fish, coral and other organisms.
  • An ecosystem consists of all the living things in a given area, together with the nonliving environment. The nonliving environment includes water, sunlight, and other physical factors.
  • A group of similar ecosystems with the same general type of physical environment is called a biome.
  • The biosphere is the part of Earth where all life exists, including all the land, water, and air where living things can be found. The biosphere consists of many different biomes.

Diversity of Life

Life on Earth is very diverse. The diversity of living things is called biodiversity.

A measure of Earth’s biodiversity is the number of different species of organisms that live on Earth. At least 10 million different species live on Earth today. They are commonly grouped into six different kingdoms. Examples of organisms within each kingdom are shown in Figure below.

Lesson Summary

  • Living things are distinguished from nonliving things on the basis of six characteristics: response to the environment, growth and development, reproduction, homeostasis, complex chemistry, and cells.
  • Three underlying principles form the basis of biology. They are cell theory, gene theory, and homeostasis.
  • Many living things interact with one another in some way. The interactions are often necessary for their survival.
  • The great diversity of life on Earth today is the result of God’s creation. He created everything to work together perfectly.

Lesson Review Questions


1. List the six characteristics of all living things.

2. Identify three unifying principles of modern biology.

3. Outline the levels of organization of a complex, multicellular organism such as a mouse, starting with the cell.

4. What is homeostasis? Give an example.

Apply Concepts

5. Describe examples of ways that you depend on other living things.

6. Assume that you found an object that looks like a dead twig. You wonder if it might be a stick insect. How could you determine if it is a living thing?

Think Critically

7. Compare and contrast symbiosis and competition.

8. Explain how a population differs from a community.

Points to Consider

In this lesson, you learned that living things have complex chemistry.

  • Do you know which chemicals make up living things?
  • All living things need energy to carry out the processes of life. Where do you think this energy comes from? For example, where do you get the energy you need to get through your day?

Opening image copyright Kirsty Pargeter, 2010. Used under license from

Symbiosis: Creatures that Need Each Others

from Discovery Magazine 9/1/2010:

Apologetics Press
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Changes/edits were made to the original ck12 biology text by Guest Hollow. Changes are not endorsed by ck12 in any way.

Coral Reefs: Ecosystems Full of Life

Students learn about reef ecology with a focus on biodiversity and symbiotic relationships in the coral reef ecosystem. They play a matching game to identify reef organisms and roles and they discuss human threats to coral reef health.

Biology, Ecology, Earth Science, Oceanography, English Language Arts, Geography, Human Geography

1. Activate students’ prior knowledge.
Ask: Have you ever heard the term biodiversity ? If so, used in what context, or way? If not, what do you think it means? Write the term on the board and model how to break the word into parts to understand its meaning. Explain that bio means "life" and diversity means "different types." Therefore, biodiversity means "different types of life." Tell students that ecosystems with high biodiversity also show a high number of symbiotic relationships between the organisms that live there. Ask: Have you ever heard the term symbiosis ? If so, can you give an example? If not, what do you think it means? Write the term on the board and model how to break the word into parts to understand its meaning, as you did with biodiversity. Explain that sym means "together" and bio means "life," so symbiosis means "life together," or "living together." To illustrate the concept of symbiosis, show students the two images in the Symbiotic Relationships photo gallery. If students have difficulty with the concept, give the example of students working together in a group to complete a task. Ask: Can you think of any ecosystems that have high biodiversity and a lot of symbiotic relationships? If students don't think of it on their own, prompt them to think of ocean ecosystems. Tell students they will watch a brief video about coral reef ecosystems.

2. Have students watch the National Geographic video “Coral Reefs.”
Before the video, ask students to pay close attention to the number and variety of animals they see on the reef and the relationships between the animals. After the video, check students' comprehension. Ask:

  • Do coral reef ecosystems have high biodiversity? Explain.
  • Do they show a lot of symbiotic relationships? Explain.
  • What organisms did you see in the video?
  • What examples of symbiotic relationships did you see in the video?

3. Have students play a game to match reef creatures and reef roles.

Have students arrange their desks in four separate groups with room for eight to ten students in each group. Project the Coral Reef Ecosystem illustration on the board so all students can see it. Place one Coral Reef Illustration Key face down at each of the four locations. If there is an odd number of students, you will need to participate or have two students work as a buddy pair that counts as one student.

  • First, randomly distribute a set of Reef Creature and Reef Role cards to each student in a group. Do this for all four groups. Explain that the "creature" cards name and describe different animals living on the coral reef. The "role" cards describe the roles and symbiotic relationships of different animals living on the reef.
  • Ask students to carefully read the information provided on their cards. Ask them to re-read to make sure they know the content of their cards.
  • Have students circulate the room in an organized manner. Students must share their card information with each classmate until they find the student that has the card that matches their own. Each creature card matches only one role card.
  • Each time two students think they have matched their cards correctly, confirm their match. If they are not a match, have them rejoin the group until they find the correct match. If they are a match, instruct them to stay together as a pair and go to one of the four locations and sit until the rest of the class is finished. While they wait, have them look at the Coral Reef Ecosystem illustration and its key, identify their reef creature, and practice describing the role the organism plays in the reef ecosystem.
  • Allow students to continue circulating until all pairs have correctly matched their cards and the pairs are in four different groups of approximately 8-10 students, or 4-5 pairs, each. Help students group themselves so that each location has a variety of creatures, not fish or invertebrates only.

4. Have students use the Coral Reef Ecosystem illustration to identify and discuss their reef creatures and roles.
If needed, give the pairs that finished last some additional time to look at the Coral Reef Ecosystem illustration and find their reef creature. Then have student pairs take turns identifying their reef creature on the projected illustration and describing to the rest of the class the role it plays in the coral reef ecosystem. To check for understanding, ask a non-presenting pair to draw a line connecting the presenting pair’s reef creature to the place or creature on the diagram that represents the role, or symbiotic relationship, the presenting pair just described. Have students discuss reasons the reef creature’s role is or is not an example of symbiosis. Support students with the discussion, as needed. Then revisit some of the same questions students discussed after the video. Ask: Do coral reefs have high biodiversity? Do they show a lot of symbiotic relationships? Explain. Ask students to support their answers with specific examples from the matching game.

5. Have students discuss human impacts to coral reefs.
Replay the video. Afterward, restate the narrator’s conclusion:

"Coral reefs have been evolving for about 500 million years. But these days they are under threat. Global warming, pollution, and overfishing have contributed to their decline. Earnest efforts are under way to protect the world’s reefs and restore them. Artificial reefs created from sunken ships and other manmade objects have shown some short-term promise, but man’s impact on the environment continues to make the future of coral reefs uncertain."

Have a whole-class discussion about how humans may negatively affect coral reef ecosystems in terms of reef biodiversity and symbiotic relationships. Ask:

  • In the video, what were three ways humans harmed coral reefs? (global warming, pollution, and overfishing)
  • What other ways could humans threaten the survival of coral reefs and the creatures living there? (Responses will vary but may include different types of pollution such as trash, plastic, chemicals, or sediment damage caused by snorkelers/divers damage, such as anchors or groundings, caused by ships and impacts from the aquarium trade.)

Informal Assessment

Assess students' ability to match their cards correctly and locate their creatures and their roles on the diagram. Check students' understanding by asking them to discuss their creatures' role in the ecosystem.

Extending the Learning

Review with students the vocabulary terms vertebrate and invertebrate. Have students identify and classify the coral reef organisms as vertebrates or invertebrates and discuss their characteristics in terms of structure and function.

4. Social constructions

Human culture is a natural phenomenon, but a natural phenomenon that has the curious property which Searle [30], in his masterful analysis, labelled the characteristic of being able to induce a kind of ‘metaphysical giddiness’. The source of that giddiness lies in the capacity for this aspect of human culture to generate an endless array of cultural variants of seemingly insubstantial form whose very existence, like the existence of omnipotent beings, can be questioned. These are the social constructions of human culture, things that we construct within our minds, which we imagine, and then share with others, and in so doing generate diversity which is at once fragile and causally hugely powerful. Money and ideology are examples of social constructions that rule, and often destroy, the lives of almost all living humans. I rely almost entirely on Searle's analysis in the following pages.

Searle was not able to provide any kind of account of how the human mind evolved the properties that it currently has𠅊nd neither can anyone else. However, he assumes, rightly, that evolved it has, and the crucial capacity that underlies social constructions is conscious intentionality, which he defines as ‘the capacity of the mind to represent objects and states of affairs of the world other than itself’ [30, pp. 6𠄷]. Conscious intentionality is caused by the mechanisms of the human brain, and hence is a physical process. Thus, all that stems from intentionality does not in any way violate a materialist approach to human culture. It does, however, provide the basis for drawing a fundamental distinction between 𠆋rute’ facts, such as the presence of sand with minimal water content in a desert, and the ‘institutional’ or ‘social’ facts, like marriage or money, which are wholly dependent upon human intentionality. Deserts would exist had humans never evolved. Marriage and money are caused only by the existence of humans with specific neural and psychological mechanisms. Money does have a physical manifestation in coins, banknotes, cheques and the like, but the value of a banknote in terms of the paper on which it is printed (value itself is a social fact) is of little consequence to those who accept it in exchange for a loaf of bread or a flight to Edinburgh marriage is a contract (a form of social fact) written on a piece of paper, but entails a string of obligations regarding children and ownership of certain goods. Brute facts are intrinsic to nature social or institutional facts are wholly dependent upon human nature (which, of course, is itself a brute fact, if a special one). This distinction between brute facts and social facts is central to Searle's analysis. In the nineteenth century, Birmingham industries manufactured hundreds of different kinds of hammers [31], different from one another in terms of their shapes and the ways in which steel and wood were blended into a single object. The wood and metal were the brute facts of hammers—the hammers' intrinsic properties. That hammers are used to drive objects together is an epistemic addition to the wood and metal that is bestowed upon it by users and observers—humans with specific psychological processes and mechanisms. What Searle did was apply this basic distinction to human social interactions. He did this by arguing for three essential elements in the creation of social facts.

The first of these elements is the psychological property of assigning function, a specific aspect of human intentionality, though he allows the possibility for some rudimentary form of it in a small number of other species. We assign functions to natural objects, such as trees providing cooling shade, but we also construct objects that fulfil specific functions, like huts and houses that give shelter. Function is thus agentive and guided by specific purpose (this is a hammer and its purpose is to drive objects together) and non-agentive, by which we ascribe functions which do not serve our intentional goals (the function of the liver is to remove toxins). One crucial form of agentive function involves our understanding that one thing stands for another. ‘Standing for something’ is the function that they have, what their purpose is. A map, whether printed on a page, drawn with a pen or scratched out in sand is a representation of spatial relationships in which intentionality stands between the person drawing the map and the person being guided by it. Maps thus convey the function of meaning in which one thing stands for another. Language, whether spoken, written or signed, is the most important form of agentive function that we impose on the brute facts of sound, vocal tract movement or the movement of our hands.

The second of Searle's elements is what he refers to as 𠆌ollective intentionality’. The notion that individuals may be drawn into a collective identity based upon a common goal has been offered by other philosophers attempting to identify key aspects of human culture [32,33]. Collective intentionality is a shared intentional state, and may embrace any number of individuals, drawing them together into a loose unit of commonly held desires and plans. A football team, with its shared desires for victory, and agreed tactics and common understanding of their opponents' weaknesses, has the properties of collective intentionality as do the supporters of a football team. The defining feature of collective intentionality for Searle is that the collective intentionality exists and stands prior to individual intentionality, the former actually being a cause of the latter. What the individual wants and knows may be caused by the group of which they are a part. Collective intentionality is central to Searle's conception of social reality. It is not simply the sum of individual intentionalities making up a group and it is not reducible to them. It is the property of human social groups essential for the construction of social reality. ‘We intend’ is not simply the sum of ‘I intend’. It is a social force in its own right, and every social or institutional fact is in part caused by collective intentionality. It is the glue of human culture and the reason why humans gain pleasure from acting together, whether that acting together involves eating with others, gossiping in the office, or going to the cinema with a friend. It is, along with language, one of the things that makes us human.

The third essential element of social reality is what Searle refers to as constitutive rules, which create the conditions for specific social activities such as playing a game, being a shareholder in a company, or entering into religious beliefs and activity. Constitutive rules form the basis of institutional or social facts. When I buy shares in a company I hand over some money (itself a social fact) in order that I may participate in the profits and losses of that company (another social fact), but do not own the enterprise yet have some small part annually in determining how that company operates. As the citizen (a social fact) of a country (also a social fact), I have certain rights and obligations within that country, but not in other countries. Humans live in a world awash with social facts, the constitutive rules of which determine how we live our lives.

Constitutive rules, the assignment of functions and collective intentionality are all necessary ingredients of social reality, which is the collective imposition of functions within a social group. Searle argues that all social reality conforms to the structure of ‘X counts as Y in C’. A share certificate (X) counts as proof of being a shareholder (Y) in the UK (C). A marriage certificate (X) counts as proof of marital status (Y) within certain countries and religious organizations (C). X counts as Y in C is iterated repeatedly to form a complex, inter-related social reality. Being a citizen of the UK (X) allows me legal status to work in Poland (Y) because both countries are members of the European Union (C), but is a form of social reality that does not extend to the United States or Brazil.

‘The connecting terms between biology and culture’ Searle concludes 𠆊re, not surprisingly, consciousness and intentionality. What is special about culture is the manifestation of collective intentionality and, in particular, the collective assignment of functions to phenomena where the function cannot be performed solely in virtue of the sheer physical features of the phenomena. From dollar bills to cathedrals, and from football games to nation-states, we are constantly encountering new social facts, where the facts exceed the physical features of the underlying physical reality’ [30, pp. 227�].

That social facts, money, legal obligations, the existence of the UK as a social fact which makes it other than a small island off the northwest coast of a northern continent, constitutes the fabric of our everyday lives, yet which is based only upon agreement, and continuing agreement, is what gives social constructions the property of ‘metaphysical giddiness’. In the recent global financial crisis, one possible solution to the UK's woes was what is called ‘quantitative easing’, which did not even entail the actual physical printing of money by the Royal mint, but merely changing the figures on the balances available to the major banks for lending to businesses. What, one is led to ask, is money but the collective agreement that it has value𠅋ut what is value? Several times in different parts of the world in the twentieth century, people stopped agreeing that money had value and traded instead in other commodities, often cigarettes. For decades, a specific ideology ruled the lives of hundreds of millions of people in Europe. The ideology, created by one person in the previous century, dictated where people could live and work, what they could earn, whether they lived free or in prison, and what they could read and, often enough, what they could say. Then in a brief period in the late 1980s, communism collapsed because people in sufficient numbers refused to agree that it was a social system of any value. About the same time, apartheid in South Africa was abandoned and the lives of non-white peoples in that part of the world changed radically. Scottish nationalists in the UK do not accept that they should be ruled by a parliament in London, just as the majority of the people of Ireland and India ceased in the twentieth century to subscribe to the belief that they were a part of Britain. Is the UK really United? Is there a European union? No one questions the existence of dry sand in the Sahara desert. But it is not difficult to look at a ꌠ note and wonder at its value. All social facts hinge upon the existence of some degree of agreement, of concerted and sustained agreement. The move from individual intentionality to collective intentionality may be, probably is, as important to the most recent evolutionary transition as the evolution of language itself.

Strange as social constructions might seem to be, there is no need to subscribe to a kind of Cartesian dualism in which this particular aspect of human culture is assigned some immaterial existence that floats ethereally between the individuals making up a culture. Social constructions are made up of the collective neural network states of individuals within social groups. There are, there must be, neurological and psychological mechanisms that give rise to social reality, and which place human social reality within the same causal framework as all other forms of human learning and knowledge. There are at least three identifiable psychological mechanisms whose neurological bases remain to be understood. The first is undeniably language, and there is no serious opposition to the Chomskian notion of language as an innate and evolved organ of mind [34,35]. Language alone, however, is unlikely to support modern human culture as it has evolved over the last 100 000 years or so. ‘Theory of mind’, the understanding that others have intentional mental states, has during the last few decades come increasingly to be understood as equal to linguistic communication in allowing us to comprehend the beliefs and knowledge of others [23,36,37], with the mirror neuron system of the brain implicated with increasing frequency as one of the mechanisms responsible for theory of mind [38�]. Mirror neurons have been observed in the brains of a number of different species of other primates, and may provide one of the bases for culture in other animals, though it should be emphasized that mirror neurons are very unlikely to be the lone causal sources of culture in any species.

There is widespread agreement on the importance of language and theory of mind in the evolution of human culture, as well as of HOKS. What is paid relatively little attention is what I have previously referred to as social force, though the notion of a conformity bias in the work of Boyd & Richerson [41] on gene𠄼ulture coevolution is a rare exception in placing social force at the centre of human culture. In the 1930s, the social psychologist Muzafer Sherif published the results of a series of studies [42] on how people within a small social group reach agreement about uncertain events. He used the visual illusion known as the autokinetic effect, where people were told to fixate their gaze on a stationary spot of light in a darkened room and after a short time the light appears to move. The subjects, not told that the apparent movement was an illusion, were asked to say how far the light had seemed to move. When tested in groups and requested to say aloud what they experienced, Sherif found that, in every case, people would rapidly home in upon an agreed amount of movement, which would eliminate the initial variation in the experienced and reported movement. People used the reported views of others to establish a frame of reference for their own judgements in short, Sherif was observing the establishment of group norms, a kind of constructive conformity which Sherif believed is a fundamental feature of human social interactions.

Sherif's work was extended by another social psychologist, Solomon Asch, in the 1950s [43], using a simple experiment that has subsequently been replicated and extended in a host of different cultures. Asch presented to a small group a vertical line on a card. He then presented to each subject another card with three lines on it and asked which of the three lines matched the length of the original. It was a simple task but only one of the group was a naive experimental subject, the rest being confederates, plants of the experimenter instructed to give in two out of three occasions the wrong answers. The situation was also rigged such that the single naive subject was always asked for their response after most of the stooges had deliberately given the wrong answers. Asch found that only one-quarter of the naive subjects stuck to their views and gave the correct answers the majority gave a clearly incorrect response that conformed with what most of the stooges had declared, or they wavered and gave answers that were uncertain and changeable. When asked why they had given what were clearly the incorrect answers, most people expressed anxiety at going against the majority view. The need to conform was greater than the evidence of their own visual experience and judgement. Subsequent studies of the Asch experiment in many different cultures have shown that while the strength of the bias to conform varies across cultures, the effect is always present. The need to conform is a universal human psychological trait.

Jacobs & Campbell [44] described an interesting variation on Sherif's original experiment with the autokinetic illusion. They put together a group in which all but one of the so-called subjects was naive, the rest being plants who grossly overstated the amount of perceived movement and the naive subject delivered her or his judgement last. In line with Sherif's findings, the single naive subject gave an overstated judgement of perceived movement. Then, one by one, the stooges were withdrawn and replaced by naive subjects until eventually the entire group comprised naive subjects. Yet the 𠆌ultural tradition’ of overstating the perceived amount of movement was maintained even when the group was made up of individuals none of whom were stooges. Here was a case of conformity operating across ‘generations’ of individuals regarding a belief based upon an illusion.

But the most powerful demonstration of what social psychologists call conformity, obedience or group cohesiveness was reported in a series of papers in the 1960s, summarized by Milgram [45]. Using actors and stooges, Milgram repeatedly demonstrated how people without any history of cruelty or violence would, when ordered to do so by a figure of authority, inflict violent punishment upon others. Milgram's studies were merely a replication under controlled conditions of what we all know of from the Holocaust inflicted on the peoples of Europe by the Nazis, depicted by Hannah Arendt as the �nality of evil’ in which ordinary people living ordinary lives will commit unspeakable acts of evil against others when those acts are sanctioned by authority and interwoven into the ordinariness of everyday life. Subsequent events in Rwanda, the Balkans and the Middle East show how the death squads and death camps of the Nazis were an expression of a universal feature of human nature, social force that leads to obedience and conformity.

Exactly how the psychological mechanisms of language, theory of mind, and social force act in concert to generate human culture, is unknown. Understanding intentional mental states in others may be present in rudimentary form in chimpanzees [46], and the existence of something like social force in other species of apes has been consistently advocated by some primatologists [47]. It may be that culture in any primates which have been observed with certainty to share knowledge, is built upon similar psychological mechanisms. And it may be that the integrated functioning of communication by way of language, the ability to comprehend the intentional mental states of others, and the existence of social force of whatever kind, is a present-day, naive, assemblage of the mechanisms of human culture. We certainly have no knowledge whatever at present as to the causal structures that will one day be understood regarding the linkages between genes, neural and psychological mechanisms. But that such causal linkages do exist, and that human culture in whatever form is a product of evolutionary forces, is not to be doubted. That is the Lorenzian lesson.


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Homeostasis, any self-regulating process by which biological systems tend to maintain stability while adjusting to conditions that are optimal for survival. If homeostasis is successful, life continues if unsuccessful, disaster or death ensues. The stability attained is actually a dynamic equilibrium, in which continuous change occurs yet relatively uniform conditions prevail.

What is homeostasis?

Homeostasis is any self-regulating process by which an organism tends to maintain stability while adjusting to conditions that are best for its survival. If homeostasis is successful, life continues if it’s unsuccessful, it results in a disaster or death of the organism. The “stability” that the organism reaches is rarely around an exact point (such as the idealized human body temperature of 37 °C [98.6 °F]). Stability takes place as part of a dynamic equilibrium, which can be thought of as a cloud of values within a tight range in which continuous change occurs. The result is that relatively uniform conditions prevail.

What is an example of homeostasis in a living thing?

Body temperature control in humans is one of the most familiar examples of homeostasis. Normal body temperature hovers around 37 °C (98.6 °F), but a number of factors can affect this value, including exposure to the elements, hormones, metabolic rate, and disease, leading to excessively high or low body temperatures. The hypothalamus in the brain regulates body temperature, and feedback about body temperature from the body is carried through the bloodstream to the brain, which results in adjustments in breathing rate, blood sugar levels, and metabolic rate. In contrast, reduced activity, perspiration, and heat-exchange processes that permit more blood to circulate near the skin surface contribute to heat loss. Heat loss is reduced by insulation, decreased circulation to the skin, clothing, shelter, and external heat sources.

What is an example of homeostasis in a mechanical system?

A familiar example of homeostatic regulation in a mechanical system is the action of a thermostat, a machine that regulates room temperature. At the centre of a thermostat is a bimetallic strip that responds to temperature changes. The strip expands under warmer conditions and contracts under cooler conditions to either disrupt or complete an electric circuit. When the room cools, the circuit is completed, the furnace switches on, and the temperature rises. At a preset level, perhaps 20 °C (68 °F), the circuit breaks, the furnace stops, and no additional heat is released into the room. Over time, the temperature slowly drops until the room cools enough to trigger the process again.

Are there examples of homeostasis in ecosystems?

The concept of homeostasis has also been used in studies of ecosystems. Canadian-born American ecologist Robert MacArthur first proposed in 1955 that homeostasis in ecosystems results from biodiversity (the variety of life in a given place) and the ecological interactions (predation, competition, decomposition, etc.) that occur between the species living there. The term homeostasis has been used by many ecologists to describe the back-and-forth interaction that occurs between the different parts of an ecosystem to maintain the status quo. It was thought that this kind of homeostasis could help to explain why forests, grasslands, or other ecosystems persist (that is, remain in the same location for long periods of time). Since 1955 the concept has changed to incorporate the ecosystem’s nonliving parts, such as rocks, soil, and water.

Any system in dynamic equilibrium tends to reach a steady state, a balance that resists outside forces of change. When such a system is disturbed, built-in regulatory devices respond to the departures to establish a new balance such a process is one of feedback control. All processes of integration and coordination of function, whether mediated by electrical circuits or by nervous and hormonal systems, are examples of homeostatic regulation.

A familiar example of homeostatic regulation in a mechanical system is the action of a room-temperature regulator, or thermostat. The heart of the thermostat is a bimetallic strip that responds to temperature changes by completing or disrupting an electric circuit. When the room cools, the circuit is completed, the furnace operates, and the temperature rises. At a preset level the circuit breaks, the furnace stops, and the temperature drops. Biological systems, of greater complexity, however, have regulators only very roughly comparable to such mechanical devices. The two types of systems are alike, however, in their goals—to sustain activity within prescribed ranges, whether to control the thickness of rolled steel or the pressure within the circulatory system.

The control of body temperature in humans is a good example of homeostasis in a biological system. In humans, normal body temperature fluctuates around the value of 37 °C (98.6 °F), but various factors can affect this value, including exposure, hormones, metabolic rate, and disease, leading to excessively high or low temperatures. The body’s temperature regulation is controlled by a region in the brain called the hypothalamus. Feedback about body temperature is carried through the bloodstream to the brain and results in compensatory adjustments in the breathing rate, the level of blood sugar, and the metabolic rate. Heat loss in humans is aided by reduction of activity, by perspiration, and by heat-exchange mechanisms that permit larger amounts of blood to circulate near the skin surface. Heat loss is reduced by insulation, decreased circulation to the skin, and cultural modification such as the use of clothing, shelter, and external heat sources. The range between high and low body temperature levels constitutes the homeostatic plateau—the “normal” range that sustains life. As either of the two extremes is approached, corrective action (through negative feedback) returns the system to the normal range.

The concept of homeostasis has also been applied to ecological settings. First proposed by Canadian-born American ecologist Robert MacArthur in 1955, homeostasis in ecosystems is a product of the combination of biodiversity and large numbers of ecological interactions that occur between species. It was thought of as a concept that could help to explain an ecosystem’s stability—that is, its persistence as a particular ecosystem type over time (see ecological resilience). Since then, the concept has changed slightly to incorporate the ecosystem’s abiotic (nonliving) parts the term has been used by many ecologists to describe the reciprocation that occurs between an ecosystem’s living and nonliving parts to maintain the status quo. The Gaia hypothesis—the model of Earth posited by English scientist James Lovelock that considers its various living and nonliving parts as components of a larger system or single organism—makes the assumption that the collective effort of individual organisms contributes to homeostasis at the planetary level. The single-organism aspect of the Gaia hypothesis is considered controversial because it posits that living things, at some level, are driven to work on behalf of the biosphere rather than toward the goal of their own survival.

The Editors of Encyclopaedia Britannica This article was most recently revised and updated by John P. Rafferty, Editor.

How are living things adapted to their environments?

Living organisms are adapted to their environment. This means that the way they look, the way they behave, how they are built, or their way of life makes them suited to survive and reproduce in their habitats. For example, giraffes have very long necks so that they can eat tall vegetation, which other animals cannot reach. The eyes of cats are like slits. That makes it possible for the cat's eyes to adjust to both bright light, when the slits are narrow, and to very dim light, when the slits are wide open.

Behavior is also an important adaptation. Animals inherit many kinds of adaptive behavior. In southern Africa there are small animals called meerkats, which live in large colonies. The meerkats take turns standing on their hind legs, looking up at the sky to spot birds of prey. Meanwhile, the meerkats in the rest of the colony go about their lives. You can probably think of many other features of body or behavior that help animals to lead a successful life.

In biology, an ecological niche refers to the overall role of a species in its environment. Most environments have many niches. If a niche is "empty" (no organisms are occupying it), new species are likely to evolve to occupy it. This happens by the process of natural selection. By natural selection, the nature of the species gradually changes to become adapted to the niche. If a species becomes very well adapted to its environment, and if the environment does not change, species can exist for a very long time before they become extinct.

An excellent example of an animal evolving to fill a niche is seen in the evolution of horses. Many fossils of different kinds of horses have been discovered, and paleontologists think that the earliest ancestor of the modern horse lived in North America more than 50 million years ago. This animal was a small padded-foot forest animal about the size of a dog. If you saw one next to a modern horse, you might not even think the two were related! As time passed, the climate of North America became drier, and the vast forests started to shrink. Grasses were evolving, and the amount grassland was increasing. Horses adapted to fill this new grassland niche. They grew taller, and their legs and feet became better adapted to sprinting in the open grasslands. Their eyes also adapted to be further back on their heads to help them to see more of the area around them. Each of these adaptations helped the evolving grassland horses to avoid predators. Their teeth also changed to be better adapted to grinding tough grassland vegetation.

Have you ever wondered what purpose the "dew" claw on the inside of a dog's paw serves? The claw is the dog's thumb. Because a dog runs on the balls of its feet and four digits, the claw no longer serves a purpose. Organs or parts of the body that no longer serve a function are called vestigial structures. They provide evidence that the species is still changing. Even humans have vestigial structures. The human appendix is one such example. It used to store microbes that helped to digest plant matter, but it is no longer needed in the human.

Our new program, the Master of Development Practice, emphasizes ‘sustainability’- but what exactly is it? Last week, we hosted a panel of 5 faculty experts to address this question. It was agreed that sustainability means that all humans are able to maintain a decent standard of living, akin to say, Costa Rica (neither Switzerland nor Bangladesh), without destroying the environment. However, physical science tells us that at the current state of affairs, this is highly unlikely. We rely too much on fossil fuels, climate change is a real threat and there are simply too many people. The challenge of sustainability is to introduction policies that will dramatically avert climate change and slow (or even reverse) population growth. The social scientists agreed that climate change is a big threat, and suggested that current political reality and distribution of powers were the main obstacles for change. There are policies that can address climate change, e.g. the carbon tax, investment in alternative technologies, various regulations designed to reduce pollution without hurting the poor, but the political system would not sustain these. Any climate change policies have gainers and losers, different groups may lose from adjustment while in the meantime, we remain stuck in the status quo. Developing countries want to grow and are investing in coal plants in the developed world, we have some notable successes such as the AB32 but they are exception, not the rule.

For a business, sustainability is not a global concept, rather a day-to-day challenge of how to stay afloat. For them, the key to sustainability is profitability. However, the business world is starting to recognize that it would not do them a lot of good to be profitable in a world that is falling apart. Furthermore, they recognize that some consumers may pay extra for products produced in a more sustainable manner, thus being ‘sustainable’ makes good business sense. With the right policy environment, the business world can be used as a tool to introduce more sustainable policies but of course many businesses may oppose such policies as they may negatively affect their bottom line.

From a life science perspective, the notion of sustainability is complex because evolution is a driving force and there is also inter-dependency among species humans eat fish, and fish depends on kelp, etc. So pollution that affects water quality may harm humans indirectly through the food web. It is clear that uncontrolled applications of technology can be devastating to eco-systems and eventually to humans as well. Thus enlightened regulations on harvesting of resources are essential. But figuring such policies and enforcing them, are major challenge, both because we operate under uncertainty and again, due to the political environment. Yet there have been some examples where things have improved for the better. While many fisheries have been depleted, there are many success stories so it can be done.

The overall perspectives of all sciences were quite pessimistic. But when I look at it, things are not that bad. Average quality of life is better than ever, life expectancy has increased throughout the world and there has been no world war for a long time and for many people, sustainability simply means making sure that their pension funds last as they reach their 80 th birthday. Even in many parts of the developing world, obesity is an issue more than hunger. Thus I think the pessimism of scientists can be a base for optimism. Awareness of risk can convince society to take steps to create change. If there is one thing we know, humans have the capacity to adapt. We may not be able to mitigate or reverse climate change, but once we realize that something needs to be done, we come to the table with innovations that will allow adjusting easier. Of course, the sooner we adjust, the more we can prevent – but the role of the University is to raise awareness and I believe that we are doing our job and in this sense, pessimism is essential. Of course, too much pessimism may be counter-productive. We have to rely on science and expand knowledge and this may require taking some risk. We may need to make changes to how we produce our food, the way we live, get our energy, etc. and this may be inconvenient to many and may entail risk. For example, living in denser cities and giving up urban sprawl, may not be convenient but it may reduce GHG emissions and environmental footprint… the price we need to pay for a more sustainable future. But I am afraid that drastic changes will require the risks be more apparent so people will be ready to make the necessary sacrifices. If there is one lesson of political economic research, crisis leads to change. I hope in the case of climate change, awareness of crisis will be enough to escape from the major threats.

13.1 Prokaryotic Diversity

Prokaryotes are present everywhere. They cover every imaginable surface where there is sufficient moisture, and they live on and inside of other living things. There are more prokaryotes inside and on the exterior of the human body than there are human cells in the body. Some prokaryotes thrive in environments that are inhospitable for most other living things. Prokaryotes recycle nutrients—essential substances (such as carbon and nitrogen)—and they drive the evolution of new ecosystems, some of which are natural while others are man-made. Prokaryotes have been on Earth since long before multicellular life appeared.

Prokaryotic Diversity

The advent of DNA sequencing provided immense insight into the relationships and origins of prokaryotes that were not possible using traditional methods of classification. A major insight identified two groups of prokaryotes that were found to be as different from each other as they were from eukaryotes. This recognition of prokaryotic diversity forced a new understanding of the classification of all life and brought us closer to understanding the fundamental relationships of all living things, including ourselves.

Early Life on Earth

When and where did life begin? What were the conditions on Earth when life began? Prokaryotes were the first forms of life on Earth, and they existed for billions of years before plants and animals appeared. Earth is about 4.54 billion years old. This estimate is based on evidence from the dating of meteorite material, since surface rocks on Earth are not as old as Earth itself. Most rocks available on Earth have undergone geological changes that make them younger than Earth itself. Some meteorites are made of the original material in the solar disk that formed the objects of the solar system, and they have not been altered by the processes that altered rocks on Earth. Thus, the age of meteorites is a good indicator of the age of the formation of Earth. The original estimate of 4.54 billion years was obtained by Clare Patterson in 1956. His meticulous work has since been corroborated by ages determined from other sources, all of which point to an Earth age of about 4.54 billion years.

Early Earth had a very different atmosphere than it does today. Evidence indicates that during the first 2 billion years of Earth’s existence, the atmosphere was anoxic , meaning that there was no oxygen. Therefore, only those organisms that can grow without oxygen— anaerobic organisms—were able to live. Organisms that convert solar energy into chemical energy are called phototrophs . Phototrophic organisms that required an organic source of carbon appeared within one billion years of the formation of Earth. Then, cyanobacteria , also known as blue-green algae, evolved from these simple phototrophs one billion years later. Cyanobacteria are able to use carbon dioxide as a source of carbon. Cyanobacteria (Figure 13.2) began the oxygenation of the atmosphere. The increase in oxygen concentration allowed the evolution of other life forms.

Before the atmosphere became oxygenated, the planet was subjected to strong radiation thus, the first organisms would have flourished where they were more protected, such as in ocean depths or beneath the surface of Earth. At this time, too, strong volcanic activity was common on Earth, so it is likely that these first organisms—the first prokaryotes—were adapted to very high temperatures. These are not the typical temperate environments in which most life flourishes today thus, we can conclude that the first organisms that appeared on Earth likely were able to withstand harsh conditions.

Microbial mats may represent the earliest forms of life on Earth, and there is fossil evidence of their presence, starting about 3.5 billion years ago. A microbial mat is a large biofilm, a multi-layered sheet of prokaryotes (Figure 13.3a), including mostly bacteria, but also archaea. Microbial mats are a few centimeters thick, and they typically grow on moist surfaces. Their various types of prokaryotes carry out different metabolic pathways, and for this reason, they reflect various colors. Prokaryotes in a microbial mat are held together by a gummy-like substance that they secrete.

The first microbial mats likely obtained their energy from hydrothermal vents. A hydrothermal vent is a fissure in Earth’s surface that releases geothermally heated water. With the evolution of photosynthesis about 3 billion years ago, some prokaryotes in microbial mats came to use a more widely available energy source—sunlight—whereas others were still dependent on chemicals from hydrothermal vents for food.

Fossilized microbial mats represent the earliest record of life on Earth. A stromatolite is a sedimentary structure formed when minerals are precipitated from water by prokaryotes in a microbial mat (Figure 13.3b). Stromatolites form layered rocks made of carbonate or silicate. Although most stromatolites are artifacts from the past, there are places on Earth where stromatolites are still forming. For example, living stromatolites have been found in the Anza-Borrego Desert State Park in San Diego County, California.

Some prokaryotes are able to thrive and grow under conditions that would kill a plant or animal. Bacteria and archaea that grow under extreme conditions are called extremophiles , meaning “lovers of extremes.” Extremophiles have been found in extreme environments of all kinds, including the depths of the oceans, hot springs, the Arctic and the Antarctic, very dry places, deep inside Earth, harsh chemical environments, and high radiation environments. Extremophiles give us a better understanding of prokaryotic diversity and open up the possibility of the discovery of new therapeutic drugs or industrial applications. They have also opened up the possibility of finding life in other places in the solar system, which have harsher environments than those typically found on Earth. Many of these extremophiles cannot survive in moderate environments.

Concepts in Action

Watch a video showing the Director of the Planetary Science Division of NASA discussing the implications that the existence extremophiles on Earth have on the possibility of finding life on other planets in our solar system, such as Mars.


Until a couple of decades ago, microbiologists thought of prokaryotes as isolated entities living apart. This model, however, does not reflect the true ecology of prokaryotes, most of which prefer to live in communities where they can interact. A biofilm is a microbial community held together in a gummy-textured matrix, consisting primarily of polysaccharides secreted by the organisms, together with some proteins and nucleic acids. Biofilms grow attached to surfaces. Some of the best-studied biofilms are composed of prokaryotes, although fungal biofilms have also been described.

Biofilms are present almost everywhere. They cause the clogging of pipes and readily colonize surfaces in industrial settings. They have played roles in recent, large-scale outbreaks of bacterial contamination of food. Biofilms also colonize household surfaces, such as kitchen counters, cutting boards, sinks, and toilets.

Interactions among the organisms that populate a biofilm, together with their protective environment, make these communities more robust than are free-living, or planktonic, prokaryotes. Overall, biofilms are very difficult to destroy, because they are resistant to many of the common forms of sterilization.

Characteristics of Prokaryotes

There are many differences between prokaryotic and eukaryotic cells. However, all cells have four common structures: a plasma membrane that functions as a barrier for the cell and separates the cell from its environment cytoplasm, a jelly-like substance inside the cell genetic material (DNA and RNA) and ribosomes, where protein synthesis takes place. Prokaryotes come in various shapes, but many fall into three categories: cocci (spherical), bacilli (rod-shaped), and spirilla (spiral-shaped) (Figure 13.4).

The Prokaryotic Cell

Recall that prokaryotes (Figure 13.5) are unicellular organisms that lack organelles surrounded by membranes. Therefore, they do not have a nucleus but instead have a single chromosome—a piece of circular DNA located in an area of the cell called the nucleoid. Most prokaryotes have a cell wall lying outside the plasma membrane. The composition of the cell wall differs significantly between the domains Bacteria and Archaea (and their cell walls also differ from the eukaryotic cell walls found in plants and fungi.) The cell wall functions as a protective layer and is responsible for the organism’s shape. Some other structures are present in some prokaryotic species, but not in others. For example, the capsule found in some species enables the organism to attach to surfaces and protects it from dehydration. Some species may also have flagella (singular, flagellum) used for locomotion, and pili (singular, pilus) used for attachment to surfaces and to other bacteria for conjugation. Plasmids, which consist of small, circular pieces of DNA outside of the main chromosome, are also present in many species of bacteria.

Both Bacteria and Archaea are types of prokaryotic cells. They differ in the lipid composition of their cell membranes and in the characteristics of their cell walls. Both types of prokaryotes have the same basic structures, but these are built from different chemical components that are evidence of an ancient separation of their lineages. The archaeal plasma membrane is chemically different from the bacterial membrane some archaeal membranes are lipid monolayers instead of phosopholipid bilayers.

The Cell Wall

The cell wall is a protective layer that surrounds some prokaryotic cells and gives them shape and rigidity. It is located outside the cell membrane and prevents osmotic lysis (bursting caused by increasing volume). The chemical compositions of the cell walls vary between Archaea and Bacteria, as well as between bacterial species. Bacterial cell walls contain peptidoglycan , composed of polysaccharide chains cross-linked to peptides. Bacteria are divided into two major groups: Gram-positive and Gram-negative , based on their reaction to a procedure called Gram staining. The different bacterial responses to the staining procedure are caused by cell wall structure. Gram-positive organisms have a thick wall consisting of many layers of peptidoglycan. Gram-negative bacteria have a thinner cell wall composed of a few layers of peptidoglycan and additional structures, surrounded by an outer membrane (Figure 13.6).

Visual Connection

Which of the following statements is true?

  1. Gram-positive bacteria have a single cell wall formed from peptidoglycan.
  2. Gram-positive bacteria have an outer membrane.
  3. The cell wall of Gram-negative bacteria is thick, and the cell wall of Gram-positive bacteria is thin.
  4. Gram-negative bacteria have a cell wall made of peptidoglycan, while Gram-positive bacteria have a cell wall made of phospholipids.

Archaeal cell walls do not contain peptidoglycan. There are four different types of archaeal cell walls. One type is composed of pseudopeptidoglycan . The other three types of cell walls contain polysaccharides, glycoproteins, and surface-layer proteins known as S-layers.


Reproduction in prokaryotes is primarily asexual and takes place by binary fission. Recall that the DNA of a prokaryote exists usually as a single, circular chromosome. Prokaryotes do not undergo mitosis. Rather, the chromosome loop is replicated, and the two resulting copies attached to the plasma membrane move apart as the cell grows in a process called binary fission. The prokaryote, now enlarged, is pinched inward at its equator, and the two resulting cells, which are clones, separate. Binary fission does not provide an opportunity for genetic recombination, but prokaryotes can alter their genetic makeup in three ways.

Binary fission as a way of reproduction does not provide an opportunity for genetic recombination and increased genetic variability. However, prokaryotes can alter their genetic makeup by three mechanisms of obtaining exogenous DNA. In a process called transformation , the cell takes in DNA found in its environment that is shed by other prokaryotes, alive or dead. A pathogen is an organism that causes a disease. If a nonpathogenic bacterium takes up DNA from a pathogen and incorporates the new DNA in its own chromosome, it too may become pathogenic. In transduction , bacteriophages, the viruses that infect bacteria, move DNA from one bacterium to another. Archaea have a different set of viruses that infect them and translocate genetic material from one individual to another. During conjugation , DNA is transferred from one prokaryote to another by means of a pilus that brings the organisms into contact with one another. The DNA transferred is usually a plasmid, but parts of the chromosome can also be moved.

Cycles of binary fission can be very rapid, on the order of minutes for some species. This short generation time coupled with mechanisms of genetic recombination result in the rapid evolution of prokaryotes, allowing them to respond to environmental changes (such as the introduction of an antibiotic) very quickly.

How Prokaryotes Obtain Energy and Carbon

Prokaryotes are metabolically diverse organisms. Prokaryotes fill many niches on Earth, including being involved in nutrient cycles such as the nitrogen and carbon cycles, decomposing dead organisms, and growing and multiplying inside living organisms, including humans. Different prokaryotes can use different sources of energy to assemble macromolecules from smaller molecules. Phototrophs obtain their energy from sunlight. Chemotrophs obtain their energy from chemical compounds.

Bacterial Diseases in Humans

Devastating pathogen-borne diseases and plagues, both viral and bacterial in nature, have affected and continue to affect humans. It is worth noting that all pathogenic prokaryotes are Bacteria there are no known pathogenic Archaea in humans or any other organism. Pathogenic organisms evolved alongside humans. In the past, the true cause of these diseases was not understood, and some cultures thought that diseases were a spiritual punishment or were mistaken about material causes. Over time, people came to realize that staying apart from afflicted persons, improving sanitation, and properly disposing of the corpses and personal belongings of victims of illness reduced their own chances of getting sick.

Historical Perspective

There are records of infectious diseases as far back as 3,000 B.C. A number of significant pandemics caused by Bacteria have been documented over several hundred years. Some of the largest pandemics led to the decline of cities and cultures. Many were zoonoses that appeared with the domestication of animals, as in the case of tuberculosis. A zoonosis is a disease that infects animals but can be transmitted from animals to humans.

Infectious diseases remain among the leading causes of death worldwide. Their impact is less significant in many developed countries, but they are important determiners of mortality in developing countries. The development of antibiotics did much to lessen the mortality rates from bacterial infections, but access to antibiotics is not universal, and the overuse of antibiotics has led to the development of resistant strains of bacteria. Public sanitation efforts that dispose of sewage and provide clean drinking water have done as much or more than medical advances to prevent deaths caused by bacterial infections.

In 430 B.C., the plague of Athens killed one-quarter of the Athenian troops that were fighting in the Great Peloponnesian War. The disease killed a quarter of the population of Athens in over 4 years and weakened Athens’ dominance and power. The source of the plague may have been identified recently when researchers from the University of Athens were able to analyze DNA from teeth recovered from a mass grave. The scientists identified nucleotide sequences from a pathogenic bacterium that causes typhoid fever. 1

From 541 to 750 A.D., an outbreak called the plague of Justinian (likely a bubonic plague) eliminated, by some estimates, one-quarter to one-half of the human population. The population in Europe declined by 50 percent during this outbreak. Bubonic plague would decimate Europe more than once.

One of the most devastating pandemics was the Black Death (1346 to 1361), which is believed to have been another outbreak of bubonic plague caused by the bacterium Yersinia pestis. This bacterium is carried by fleas living on black rats. The Black Death reduced the world’s population from an estimated 450 million to about 350 to 375 million. Bubonic plague struck London hard again in the mid-1600s. There are still approximately 1,000 to 3,000 cases of plague globally each year. Although contracting bubonic plague before antibiotics meant almost certain death, the bacterium responds to several types of modern antibiotics, and mortality rates from plague are now very low.

Concepts in Action

Watch a video on the modern understanding of the Black Death (bubonic plague) in Europe during the fourteenth century.

Over the centuries, Europeans developed resistance to many infectious diseases. However, European conquerors brought disease-causing bacteria and viruses with them when they reached the Western hemisphere, triggering epidemics that completely devastated populations of Native Americans (who had no natural resistance to many European diseases).

The Antibiotic Crisis

The word antibiotic comes from the Greek anti, meaning “against,” and bios, meaning “life.” An antibiotic is an organism-produced chemical that is hostile to the growth of other organisms. Today’s news and media often address concerns about an antibiotic crisis. Are antibiotics that were used to treat bacterial infections easily treatable in the past becoming obsolete? Are there new “superbugs”—bacteria that have evolved to become more resistant to our arsenal of antibiotics? Is this the beginning of the end of antibiotics? All of these questions challenge the healthcare community.

One of the main reasons for resistant bacteria is the overuse and incorrect use of antibiotics, such as not completing a full course of prescribed antibiotics. The incorrect use of an antibiotic results in the natural selection of resistant forms of bacteria. The antibiotic kills most of the infecting bacteria, and therefore only the resistant forms remain. These resistant forms reproduce, resulting in an increase in the proportion of resistant forms over non-resistant ones.

Another problem is the excessive use of antibiotics in livestock. The routine use of antibiotics in animal feed promotes bacterial resistance as well. In the United States, 70 percent of the antibiotics produced are fed to animals. The antibiotics are not used to prevent disease, but to enhance production of their products.

Concepts in Action

Watch an overview report on the problem of routine antibiotic administration to livestock and antibiotic-resistant bacteria.

Staphylococcus aureus, often called “staph,” is a common bacterium that can live in and on the human body, which usually is easily treatable with antibiotics. A very dangerous strain, however, has made the news over the past few years (Figure 13.7). This strain, methicillin-resistant Staphylococcus aureus (MRSA), is resistant to many commonly used antibiotics, including methicillin, amoxicillin, penicillin, and oxacillin. While MRSA infections have been common among people in healthcare facilities, it is appearing more commonly in healthy people who live or work in dense groups (like military personnel and prisoners). The Journal of the American Medical Association reported that, among MRSA-afflicted persons in healthcare facilities, the average age is 68 years, while people with “community-associated MRSA” (CA-MRSA) have an average age of 23 years. 2

In summary, society is facing an antibiotic crisis. Some scientists believe that after years of being protected from bacterial infections by antibiotics, we may be returning to a time in which a simple bacterial infection could again devastate the human population. Researchers are working on developing new antibiotics, but few are in the drug development pipeline, and it takes many years to generate an effective and approved drug.

Foodborne Diseases

Prokaryotes are everywhere: They readily colonize the surface of any type of material, and food is not an exception. Outbreaks of bacterial infection related to food consumption are common. A foodborne disease (colloquially called “food poisoning”) is an illness resulting from the consumption of food contaminated with pathogenic bacteria, viruses, or other parasites. Although the United States has one of the safest food supplies in the world, the Center for Disease Control and Prevention (CDC) has reported that “76 million people get sick, more than 300,000 are hospitalized, and 5,000 Americans die each year from foodborne illness.” 3

The characteristics of foodborne illnesses have changed over time. In the past, it was relatively common to hear about sporadic cases of botulism , the potentially fatal disease produced by a toxin from the anaerobic bacterium Clostridium botulinum. A can, jar, or package created a suitable anaerobic environment where Clostridium could grow. Proper sterilization and canning procedures have reduced the incidence of this disease.

Most cases of foodborne illnesses are now linked to produce contaminated by animal waste. For example, there have been serious, produce-related outbreaks associated with raw spinach in the United States and with vegetable sprouts in Germany (Figure 13.8). The raw spinach outbreak in 2006 was produced by the bacterium E. coli strain O157:H7. Most E. coli strains are not particularly dangerous to humans, (indeed, they live in our large intestine), but O157:H7 is potentially fatal.

All types of food can potentially be contaminated with harmful bacteria of different species. Recent outbreaks of Salmonella reported by the CDC occurred in foods as diverse as peanut butter, alfalfa sprouts, and eggs.

Career Connection


Epidemiology is the study of the occurrence, distribution, and determinants of health and disease in a population. It is, therefore, related to public health. An epidemiologist studies the frequency and distribution of diseases within human populations and environments.

Epidemiologists collect data about a particular disease and track its spread to identify the original mode of transmission. They sometimes work in close collaboration with historians to try to understand the way a disease evolved geographically and over time, tracking the natural history of pathogens. They gather information from clinical records, patient interviews, and any other available means. That information is used to develop strategies and design public health policies to reduce the incidence of a disease or to prevent its spread. Epidemiologists also conduct rapid investigations in case of an outbreak to recommend immediate measures to control it.

Epidemiologists typically have a graduate-level education. An epidemiologist often has a bachelor’s degree in some field and a master’s degree in public health (MPH). Many epidemiologists are also physicians (and have an MD) or they have a PhD in an associated field, such as biology or epidemiology.

Beneficial Prokaryotes

Not all prokaryotes are pathogenic. On the contrary, pathogens represent only a very small percentage of the diversity of the microbial world. In fact, our life and all life on this planet would not be possible without prokaryotes.

Prokaryotes, and Food and Beverages

According to the United Nations Convention on Biological Diversity, biotechnology is “any technological application that uses biological systems, living organisms, or derivatives thereof, to make or modify products or processes for specific use.” 4 The concept of “specific use” involves some sort of commercial application. Genetic engineering, artificial selection, antibiotic production, and cell culture are current topics of study in biotechnology. However, humans have used prokaryotes to create products before the term biotechnology was even coined. And some of the goods and services are as simple as cheese, yogurt, sour cream, vinegar, cured sausage, sauerkraut, and fermented seafood that contains both bacteria and archaea (Figure 13.9).

Cheese production began around 4,000 years ago when humans started to breed animals and process their milk. Evidence suggests that cultured milk products, like yogurt, have existed for at least 4,000 years.

Using Prokaryotes to Clean up Our Planet: Bioremediation

Probably one of the most useful and interesting examples of the use of prokaryotes for bioremediation purposes is the cleanup of oil spills. The importance of prokaryotes to petroleum bioremediation has been demonstrated in several oil spills in recent years, such as the Exxon Valdez spill in Alaska (1989) (Figure 13.10), the Prestige oil spill in Spain (2002), the spill into the Mediterranean from a Lebanon power plant (2006,) and more recently, the BP oil spill in the Gulf of Mexico (2010). To clean up these spills, bioremediation is promoted by adding inorganic nutrients that help bacteria already present in the environment to grow. Hydrocarbon-degrading bacteria feed on the hydrocarbons in the oil droplet, breaking them into inorganic compounds. Some species, such as Alcanivorax borkumensis, produce surfactants that solubilize the oil, while other bacteria degrade the oil into carbon dioxide. In the case of oil spills in the ocean, ongoing, natural bioremediation tends to occur, inasmuch as there are oil-consuming bacteria in the ocean prior to the spill. Under ideal conditions, it has been reported that up to 80 percent of the nonvolatile components in oil can be degraded within 1 year of the spill. Other oil fractions containing aromatic and highly branched hydrocarbon chains are more difficult to remove and remain in the environment for longer periods of time. Researchers have genetically engineered other bacteria to consume petroleum products indeed, the first patent application for a bioremediation application in the U.S. was for a genetically modified oil-eating bacterium.

Prokaryotes in and on the Body

Humans are no exception when it comes to forming symbiotic relationships with prokaryotes. We are accustomed to thinking of ourselves as single organisms, but in reality, we are walking ecosystems. There are 10 to 100 times as many bacterial and archaeal cells inhabiting our bodies as we have cells in our bodies. Some of these are in mutually beneficial relationships with us, in which both the human host and the bacterium benefit, while some of the relationships are classified as commensalism , a type of relationship in which the bacterium benefits and the human host is neither benefited nor harmed.

Human gut flora lives in the large intestine and consists of hundreds of species of bacteria and archaea, with different individuals containing different species mixes. The term “flora,” which is usually associated with plants, is traditionally used in this context because bacteria were once classified as plants. The primary functions of these prokaryotes for humans appear to be metabolism of food molecules that we cannot break down, assistance with the absorption of ions by the colon, synthesis of vitamin K, training of the infant immune system, maintenance of the adult immune system, maintenance of the epithelium of the large intestine, and formation of a protective barrier against pathogens.

The surface of the skin is also coated with prokaryotes. The different surfaces of the skin, such as the underarms, the head, and the hands, provide different habitats for different communities of prokaryotes. Unlike with gut flora, the possible beneficial roles of skin flora have not been well studied. However, the few studies conducted so far have identified bacteria that produce antimicrobial compounds as probably responsible for preventing infections by pathogenic bacteria.

Researchers are actively studying the relationships between various diseases and alterations to the composition of human microbial flora. Some of this work is being carried out by the Human Microbiome Project, funded in the United States by the National Institutes of Health.

Watch the video: Κατασκευάζοντας πλαστικά που δεν καταστρέφουν το περιβάλλον.. - hi-tech (February 2023).