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What is the evolutionary advantage of menstruation?

What is the evolutionary advantage of menstruation?


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I was wondering why woman have fertile periods. Based on some simple reasoning I would expect that if woman were always fertile this would increase the chance of reproduction(one of the important things in life). But having menstrual periods would decrease this chance because only the period close to ovulation would result in fertilization.
So why did evolution result in woman having menstrual cycles?


Human female ovaries only have a certain number of ova; none are manufactured in adulthood. Once they're gone (that's when menopause occurs), they're gone.

You can also ask, why did evolution result in a limited number of oocytes then? This kind of second guessing of physiology is endless.

In your scenario, an ovum would need to be released every few days in order to be fertile continuously. That alone would decrease the number of years that a woman could be fertile. Since a fetus needs about nine months to gestate, I think once a month fertility is more than adequate. The earth's population is already too large, which also translates as successful reproductively.

If a fetus could gestate in a month, I could see an advantage to constant fertility. But the disadvantages would also be great. How could a woman take care of so many babies? How could she possibly feed, say, six to nine babies a year with only two breasts? (Mammals that frequently have larger litters have more mammary glands.) How could her own body compensate nutritionally not only for the burden of feeding the fetuses but also of the babies?

Asking why didn't something evolve from a teleological standpoint rarely results in a satisfying answer. If constant fertility were advantageous, maybe it would be present.


A long childhood is of advantage

While it may seem like kids grow up too fast, evolutionary anthropologists see things differently. Human childhood is considerably longer than chimpanzees, our closest-living ape relatives. A multinational team of researchers from the Max Planck Institute for Evolutionary Anthropology, Harvard University and the European Synchrotron Radiation Facility found a similar pattern when human kids are compared to Neanderthals. The specialists applied cutting-edge synchrotron X-ray imaging to resolve microscopic growth in 10 young Neanderthal and Homo sapiens fossils and found that despite some overlap, which is common in closely-related species, significant developmental differences exist. Modern humans are the slowest to the finish line, stretching out their maturation, which may have given them a unique evolutionary advantage (PNAS, November 15, 2010).

State-of-the-art synchrotron imaging of the tiny upper jaw of a Neanderthal child allows scientists to count tiny growth lines inside the first molar teeth and determine that it died at age 3.

© Fossil courtesy: Université de Liège, Belgium Photo credit: Graham Chedd, Paul Tafforeau, Tanya Smith

Evolutionary biology has shown that small changes during early development may lead to differences that result in new species. These changes may take the form of modifications in the sequence or timing of developmental events thus understanding developmental transformation is key to reconstructing evolutionary history. Anthropologists have documented many differences in adult characteristics among closely related species, such as humans and chimpanzees. Genomic data combined with fossil evidence indicate that these two lineages split six to seven million years ago, and have since been evolving separately. However, we know much less about which changes led to the separate lineages, how these changes arose, and when they occurred. Research during the past two decades has shown that early fossil humans (australopithecines and early members of the genus Homo) possessed short growth periods, which were more similar to chimpanzees than to living humans. However, it has been unclear when, and in which group of fossil humans, the modern condition of a relatively long childhood arose.

One poorly understood change is our unique life history, or the way in which we time growth, development, and reproductive efforts. Compared to humans, non-human primate life history is marked by a shorter gestation period, faster post-natal maturation rates, younger age at first reproduction, shorter post-reproductive period, and a shorter overall lifespan. For example, chimpanzees reach reproductive maturity several years before humans, bearing their first offspring by age 13, in contrast to the human average of 19. "The slow development in children is directly related to the emergence of human social and cultural complexity", says Jean-Jacques Hublin, director at the Max Planck Institute for Evolutionary Anthropology (MPI-EVA) in Leipzig, Germany. "It allows a long maturation of the brain and an extended education period" he explains.

Virtually reconstructed dentition of a Neanderthal child from France. Synchrotron virtual histology reveals precise developmental information that is recorded in the form of tiny growth tracks inside the teeth (background).

© Fossil courtesy: National Archeology Museum, Saint Germain en Laye, France Photo credit: Paul Tafforeau, Tanya Smith

It might seem that life history is invisible in the fossil record, but it turns out that many life history variables correlate strongly with dental development. "Teeth are remarkable time recorders, capturing each day of growth much like rings in trees reveal yearly progress. Even more impressive is the fact that our first molars contain a tiny ‘birth certificate’, and finding this birth line allows scientists to calculate exactly how old a juvenile was when it died" says Tanya Smith, a researcher from Harvard University and the Max Planck Institute for Evolutionary Anthropology. This forensic approach to the past is possible with a ‘super-microscope:’ extremely powerful X-ray beams produced at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France (www.esrf.eu), which is one of the largest synchrotron in the world. The ESRF researcher Paul Tafforeau notes: "At the ESRF, we are able to look inside invaluable fossils without damaging them by using the special properties of high energy synchrotron X-rays. We can investigate fossils at different scales and in three-dimensions, ranging from studies of overall 3D shape down to microscopic daily growth lines. This is currently the only place where these studies of fossil humans are possible." Scientists and curators have been quietly visiting the French synchrotron, often with some of the rarest hominin fossils in the world, for imaging with this state-of-the-art technique.

Scientists have been debating whether Neanderthals grew differently than modern humans for decades. An ambitious project on the development of these archaic humans was launched by Jean-Jacques Hublin and colleagues at the Max Planck Institute for Evolutionary Anthropology (www.eva.mpg.de). The study by Smith, Tafforeau and other specialists includes some of the most famous Neanderthal children, including the first hominin fossil ever discovered (Figure 2). This Belgian Neanderthal child, discovered in the winter of 1829-1830, was thought to be 4-5 years of age when it died. Powerful synchrotron X-rays and cutting-edge imaging software revealed that it actually died at a mere 3 years of age. Another invaluable Neanderthal discovered in Le Moustier, France in 1908, barely survived the shelling of its’ German repository during the Second World War (Figure 3). A remarkable finding of this five-year study is that Neanderthals grow their teeth significantly faster than members of our own species, including some of the earliest groups of modern humans to leave Africa between 90-100,000 years ago. The Neanderthal pattern appears to be intermediate between early members of our genus (e.g., Homo erectus) and living people, suggesting that the characteristically slow development and long childhood is a recent condition unique to our own species. This extended period of maturation may facilitate additional learning and complex cognition, possibly giving early Homo sapiens a competitive advantage over their contemporaneous Neanderthal cousins.

Studies by Smith, Tafforeau and a number of scientists at the MPI-EVA are adding to the growing body of evidence that subtle developmental differences exist between us and our Neanderthal cousins. A study recently published in Current Biology by Philipp Gunz and colleagues reports that brain development also differs between Neanderthals and modern humans. Moreover, the recent sequencing of the Neanderthals genome by MPI-EVA molecular biologists around Svante Pääbo has provided tantalizing genetic clues that point to differences in cranial and skeletal development between Neanderthals and modern humans. These new methods present a unique opportunity to assess the origins of a fundamentally human condition: the costly yet advantageous shift from a primitive "live fast and die young" strategy to the "live slow and grow old" strategy that has helped to make us one of the most successful organisms on the planet.


Abstract

Reciprocal coevolution between host and pathogen is widely seen as a major driver of evolution and biological innovation. Yet, to date, the underlying genetic mechanisms and associated trait functions that are unique to rapid coevolutionary change are generally unknown. We here combined experimental evolution of the bacterial biocontrol agent Bacillus thuringiensis and its nematode host Caenorhabditis elegans with large-scale phenotyping, whole genome analysis, and functional genetics to demonstrate the selective benefit of pathogen virulence and the underlying toxin genes during the adaptation process. We show that: (i) high virulence was specifically favoured during pathogen–host coevolution rather than pathogen one-sided adaptation to a nonchanging host or to an environment without host (ii) the pathogen genotype BT-679 with known nematocidal toxin genes and high virulence specifically swept to fixation in all of the independent replicate populations under coevolution but only some under one-sided adaptation (iii) high virulence in the BT-679-dominated populations correlated with elevated copy numbers of the plasmid containing the nematocidal toxin genes (iv) loss of virulence in a toxin-plasmid lacking BT-679 isolate was reconstituted by genetic reintroduction or external addition of the toxins. We conclude that sustained coevolution is distinct from unidirectional selection in shaping the pathogen's genome and life history characteristics. To our knowledge, this study is the first to characterize the pathogen genes involved in coevolutionary adaptation in an animal host–pathogen interaction system.


Introduction

Live vaccines replicate within the host. As true of any reproducing population, these within-host vaccine populations may evolve. For live vaccines that do not transmit, any within-host evolution is a dead end and might thus seem to be irrelevant to vaccine function. But if the process is fast enough, or the vaccine population replicates long enough, the vaccine population may evolve to a state where it is ineffective or virulent—either change would be bad.

The two main types of live viral vaccines are attenuated and recombinant-vectored. Most live virus vaccines in use today are attenuated, their reduced virulence typically achieved by adapting the wild-type virus to a new environment (e.g. replication in a novel cell line or low temperature), with a consequent reduced replication rate in humans. The use of attenuated vaccines is too risky for pathogens such as HIV, and a safer alternative is to develop a live, recombinant vector vaccine where one or a few pathogen genes with immunogenic activity (proteins that elicit protective immunity) are expressed from a benign virus vector.

The expected consequences of within-host evolution differ between these two types of vaccines (Table 1). Evolution of an attenuated vaccine is likely to be a reversion toward the wild-type state, the rate of this process depending heavily on vaccine design and the duration of vaccine virus replication in the host (reviewed in [1]). To a first approximation, reversion toward the wild-type state should lead to the vaccination more closely resembling natural infection [2], such as higher virus densities, side-effects and disease, and possibly an increased immune response. Within-host evolution of an attenuated vaccine might also predispose the virus to better transmission—also reflecting the wild-type state—but this outcome is not assured: viral adaptation to different tissues within the host may hamper growth in and dissemination from tissues important in transmission (e.g., [3]).

The expected consequences for evolution of a recombinant-vectored vaccine are fundamentally different [4]. In most cases, the antigen against which immunity is sought comes from a foreign transgene inserted into a competent viral vector without replacing any vector genes. Vectors in development include adenovirus, VSV (vesicular stomatitis virus) and CMV (cytomegalovirus). The vector genome carries out all viral amplification and transmission functions, and the transgene does not contribute to any process benefiting vector reproduction. From an evolutionary perspective, the transgene is both dispensable and potentially costly: selection may favor loss of the transgene and thus loss of vaccine’s ability to elicit immunity against the antigen encoded by the transgene. This evolution therefore generates something akin to infection by the wild-type vector. As vectors are typically chosen to be avirulent for immune competent hosts, vaccine evolution will result in no more than a harmless infection that does not generate immunity to the antigen encoded by the transgene.

Considerable attention has recently been given to the evolution of attenuated vaccines and designs that retard their evolution. Evolutionary stability of attenuated vaccines seems attainable by engineering designs, including the introduction of hundreds of silent codon changes, genome rearrangements, and some types of deletions (comparisons and reviews are provided by [1, 5, 6]). Far less thought has gone into the consequences of evolution for recombinant vector vaccines or of strategies to minimize this evolution.

Although recombinant vector vaccines are not yet in widespread use, many are under development [7, 8], and their success may rest on understanding within-host evolution. Here we explore how the combination of evolution during the process of vaccine manufacture and during its within-host dynamics following vaccination could affect the immune responses elicited by a recombinant vector vaccine and reduce its efficacy—the specific interaction between evolution and immunity. We consider viral vaccines and focus on vaccines that cause short-duration (acute) infections. The ideas we discuss also apply to live vaccines of bacteria and other pathogens.

Our overall message is that while vaccine evolution may occur, it is either unlikely to be a problem (i.e., compromise the generation of immunity), or it is easily mitigated. When vaccine evolution does limit the adaptive immune response, we identify ways of escaping such outcomes. Our analysis rests on mathematical models, but most results can be explained intuitively (perhaps only in hindsight), with the main results illustrated graphically many analyses are relegated to Supporting Information. Our analysis assumes that vaccines replicate within the host untill cleared by host immunity we exclude vaccines that reproduce for just a single infection cycle (e.g., Modified Vaccinia Virus Ankara), as they have no significant opportunity for evolution.


Selection Shadows

Over time, natural selection should improve a species’ ability to survive and reproduce. So why do we die of old age? Surely a mutation that increases individuals’ risk of death should have been stamped out somewhere along the evolutionary path?

Until the 20th century, many biologists thought that natural selection favoured old age because it made space for the next generation. If too many people lingered, the group as a whole would suffer . But there was a problem with this logic: the longer individuals live, the more offspring they generally leave. Death might create more room, but it won’t help a species survive .

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In the 1940s, biologists J.B.S. Haldane and Peter Medawar suggested an alternative explanation . For most species, individuals are usually killed before they reach old age. The pair argued that because the species' survival therefore rests on youthful individuals, natural selection shouldn’t favour harmful mutations that affect the young.

In contrast, only a few individuals survive to old age, so evolution won’t be so efficient at mopping up mutations that are harmful to the elderly. In other words, the elderly are in a “selection shadow”, with mutations leading to old age – and its negative effects – creeping in as the species evolves over time.

It was a nice theory, but at the time there was no evidence that natural selection could purge harmful mutations in the young, but miss them in the elderly. The breakthrough came in 1966, when William Hamilton tackled the problem mathematically . By examining the relationship between evolution and mortality, he showed that mutations in older age groups should have less effect on a species’ long-term survival. Just as Haldane and Medawar had predicted, the “force of natural selection” declines with age.

Hamilton’s paper was a significant advance, but it had some important drawbacks. First, Hamilton assumed that natural selection was linear: two copies of a harmful mutation had twice the effect of one. He also analysed a population was genetically the same, with all individuals having the same number and type of mutations.


Flowers and Fruits as an Evolutionary Adaptation

Evolution Connection

Building Phylogenetic Trees with Analysis of DNA Sequence AlignmentsAll living organisms display patterns of relationships derived from their evolutionary history. Phylogeny is the science that describes the relative connections between organisms, in terms of ancestral and descendant species. Phylogenetic trees, such as the plant evolutionary history shown in Figure, are tree-like branching diagrams that depict these relationships. Species are found at the tips of the branches. Each branching point, called a node, is the point at which a single taxonomic group (taxon), such as a species, separates into two or more species.

This phylogenetic tree shows the evolutionary relationships of plants.

Phylogenetic trees have been built to describe the relationships between species since Darwin’s time. Traditional methods involve comparison of homologous anatomical structures and embryonic development, assuming that closely related organisms share anatomical features during embryo development. Some traits that disappear in the adult are present in the embryo for example, a human fetus, at one point, has a tail. The study of fossil records shows the intermediate stages that link an ancestral form to its descendants. Most of these approaches are imprecise and lend themselves to multiple interpretations. As the tools of molecular biology and computational analysis have been developed and perfected in recent years, a new generation of tree-building methods has taken shape. The key assumption is that genes for essential proteins or RNA structures, such as the ribosomal RNA, are inherently conserved because mutations (changes in the DNA sequence) could compromise the survival of the organism. DNA from minute amounts of living organisms or fossils can be amplified by polymerase chain reaction (PCR) and sequenced, targeting the regions of the genome that are most likely to be conserved between species. The genes encoding the ribosomal RNA from the small 18S subunit and plastid genes are frequently chosen for DNA alignment analysis.

Once the sequences of interest are obtained, they are compared with existing sequences in databases such as GenBank, which is maintained by The National Center for Biotechnology Information. A number of computational tools are available to align and analyze sequences. Sophisticated computer analysis programs determine the percentage of sequence identity or homology. Sequence homology can be used to estimate the evolutionary distance between two DNA sequences and reflect the time elapsed since the genes separated from a common ancestor. Molecular analysis has revolutionized phylogenetic trees. In some cases, prior results from morphological studies have been confirmed: for example, confirming Amborella trichopoda as the most primitive angiosperm known. However, some groups and relationships have been rearranged as a result of DNA analysis.


What is the evolutionary advantage of menstruation? - Biology

Human development in an evolutionary perspective*

El desarrollo humano en una perspectiva evolucionista

Maria Lucia Seidl-de-Moura**
Ângela Donato Oliva**
Mauro Luis Vieira***

* Prof. Vieira would like to acknowledge the contributions of Alessandra Prado, Gabriela Martins, and Samira Macarini on previous drafts of this paper. Profs. Vieira and Seidl-de-Moura have grants from the Brazilian National Research Council, CNPq.

** Universidade do Estado do Rio de Janeiro (Brazil). Corresponding address: Maria Lucia Seidl-de-Moura. Fritz Feigl, 465, Rio de Janeiro, RJ, Brazil 22750-600. E-mail: [email protected]

*** Universidade Federal de Santa Catarina (Brazil).

Fecha de recepción: 21 de noviembre de 2008
Fecha de aceptación: 8 de noviembre de 2009

This article presents an evolutionary perspective to the study of human development. Some general assumptions for the study of development are discussed and the principal building blocks of evolutionary psychology are presented. One of them is that there is a universal human nature (which is modulate also by particular conditions of each context) and the cognitive architecture of human beings is the resulted of interactions between genes and environment. Based on those, and other assumptions, directions for the study of child development in an evolutionary stance are discussed, along with the considerations of context and development. Thus, it is assumed there is a relationship between phylogenies and ontogenetic development (the ontogenesis needs to be understood also as a product of evolution), considering the inseparability of biological, socio-cultural, cognitive emotional aspects that constitute this development. It has been concluded that the evolutionary developmental psychology has scientific relevance because it broadens our vision on human development.

Key words: human development evolutionary developmental psychology biology and culture phylogeny and ontogeny.

Este artículo presenta una perspectiva evolucionista del estudio del desarrollo humano. Se discuten algunas suposiciones generales para el estudio del desarrollo y se presentan las principales bases de la psicología evolucionista. Uno de estos principios es que existe una naturaleza humana universal (la cual es también modulada por condiciones particulares de cada contexto) y que la arquitectura cognoscitiva de los seres humanos es el resultado de las interacciones entre genes y ambiente. Con base en éstas y otras suposiciones, se debaten las directrices para el estudio del desarrollo infantil desde un punto de vista evolucionista, junto con las consideraciones del contexto y el desarrollo. Así, se asume que hay una relación entre las filogenias y el desarrollo ontogenético (la ontogenia requiere ser entendida también como un producto de la evolución), considerando la inseparabilidad de los aspectos biológicos, socio-culturales, cognoscitivos y emocionales que constituyen este desarrollo. Se concluye que la psicología evolucionista del desarrollo tiene relevancia científica pues amplía nuestra visión del desarrollo humano.

Palabras clave: desarrollo humano psicología evolucionista del desarrollo biología y cultura filogenia y ontogenia.

Developmental psychology has had its origins in the biological thought, based in the Theory of Evolution (Bjorklund & Pellegrini, 2000). The authors who became classical in the area and brought great contribution to the study of human development such as J. Baldwin (1890-1968), A. Gesell (1880-1961), J. Piaget (1896-1980), L. S. Vygotsky (1896-1834), among others, were influenced by evolutionary ideas. Despite this beginning, after the first decades of the last century, we can observe a decline of this influence in the explanations of human ontogeny.

We assume that to understand human development it is necessary to consider the relation between biology and culture, and the inseparability of different planes of analysis: philogenetic, ontogenetic, historical-cultural and microgenetic. With this assumption, to consider development in the ontogenesis is to think of a process that occurs in a historical time and in a context, and that in itself is a product of evolution by natural selection, along our constitution as a species. Humans have certain characteristics and they develop according to certain processes which translate in products with forms and functions. Thus, it is as a product of evolution that ontogenesis needs to be understood. This understanding should be incorporated to explanations of human mind and behavior in evolutionary perspectives.

Considering the level of analysis of the individuals of the species across the life span, it is important to take seriously the notion of development as a process and not a collection of products or results, or individual accomplishments or capacities. Studies in the area of developmental psychology often focus on products of development as relatively stable states. In doing so, they neglect the understanding of the interrelation of the determining factors and the complexity of the subjacent processes. Examples of this tendency are studies about early infant development. Although very relevant, many of them consider static capacities of newborns, for instance, without any evolutionary considerations about their function and how they fit in a human mind. Certainly it is important to follow the development of mental processes. Nevertheless, although the studies of capacities of newborns bring light to essential aspects of initial development, the notion of initial state needs to be qualified. It can not be restricted to birth. It is necessary to analyze preparatory stages before that and, at the same time, to recognize other crucial moments in subsequent stages of development. It is not enough either to focus on performance in varied abilities at different age levels. What should be the aim of developmental psychology is to analyze behavioral and representational changes across the life spam and to formulate hypotheses about the processes or mechanisms that produce those changes.

Conceptions of development are multiple, and are not going to be discussed here. What is important is to stress, among the ideas presented in the literature, some that are compatible with the perspective presented here. Van Geert (1998) considers that development involves transformations and a great number of influences. The transformations are produced by interactions of different levels. The systems approach to development emphasizes those interactions. The key notion is that of epigenesis. New relations are constructed across the development, reflecting bi-directional relations at all behavioral (including a complex interaction between environmental influences) and biological levels. (Bjorklund & Pellegrini, 2002). Structure and functioning levels (molecular, sub-cellular, cellular and of the organism) are considered. Functioning at each level influences and it is influenced by the others. Development represents a growth of complexity and organization at all levels as products of reciprocal actions between them. There is no separation of what is genetic and what is environment influence, because it is considered that genes-environment interaction occurs at all levels including the molecular one.

Individual development is probabilistic and unpredictable, resulting from the articulation of bi-directional influences between environment (physical, social and/or cultural), behavior, neural and genetic. Individual experiences begin before birth (for instance moving in the uterus or hearing mother's voice), are unique and enter in a nonlinear equation. Bjorklund and Pellegrini (2000) defend the idea of systems of development which include the genes and the multiple environments both internal and external in which the genes exist. What are transmitted are development resources which inter-act (genes, necessary apparatus for their functioning, and the broader context of development). Thus, individuals inherit not only a species specific genome, but, also, an environment typical of the specie. Some examples of characteristics of this environment are pregnancy, nursing, necessary parental care as consequence of the initial dependency, etc. (Keller, 2007). This environment is a system of contexts of several levels. Bronfrenbrenner (1986) has described several levels of context that potentially influence development (i.e., the microsystem –for example, the child's home, school, etc., the mesosystem– a group of microsystems, the, the government or economic system where the child lives, and the macrosystems -, for example, the child's culture). Organisms and environments interact in a singular ways at different moments of the life cycle. There are specific tendencies, characteristic of the specie, for certain behaviors such as the one of attachment, for instance. However, the way those mechanisms, products of evolution, express themselves varies depending on the environmental conditions experienced at certain moments of development, that also vary. Those conditions can be described as developmental niches (Harkness & Super, 1996), which are interrelated sub-systems: the social and physical environment, the shared practices of care and the psychology of caregivers. This idea will be presented with more details in other part of this paper.

The conception of ontogenetic development presented here follows the perspective of a psychology oriented by the biology of evolution, which represents a recent tendency in the area, the perspective of the Evolutionary Psychology (EP), and specifically, the Evolutionary Developmental Psychology.

It is important to consider the evolutionary perspective of development, but we emphasize that this does not exclude other contributions. The Evolutionary Developmental Psychology (EDP) should be integrated and understood under that perspective in a way that tries to incorporate the recommendations of both Vygotsky (about considering in development the inseparability of different planes of analyses) and Tinbergen (1963) (presented in next section, about providing the answer of the four basic questions) (Bjorklund & Pellegrini, 2002). Thus, this paper introduces an evolutionary proposal of a conception of ontogenetic development, considering the inseparability of biological, socio-cultural, cognitive emotional aspects that constitute this development.

Evolutionary psychology

When we formulate the question "Why are we the way we are?" the Theory of evolution offers some of the most inspiring answers from the scientific point of view. N. Tinbergen (1963) formulated the well known recommendation of the four categories of questions that should be answered related to behavior: 1) what are the stimuli that elicit the response, and how has it been modified by recent learning? How do behavior and psyche "function" on the molecular, physiological, neuro-ethological, cognitive and social level, and what do the relations between the levels look like? (Related to the proximate mechanisms –the immediate influences of behavior) 2) how does the behavior impact on the animal's chances of survival and reproduction? What are the selective advantages? (Related to function of behavior or adaptation –the adaptive purpose) 3) how does the behavior change with age, and what early experiences are necessary for the behavior to be shown? Which developmental steps (the ontogenesis follows an "inner plan") and which environmental factors play when/which role? (Related to the ontogeny –the developmental influences on behavior) 4) how does the behavior compare with similar behavior in related species and how might it have arisen through the process of phylogeny? (Related to the phylogeny– the evolutionary or philogenetic origins of behavior). This was very much considered in ethological studies, but more or less ignored in psychology.

EP is a young scientific field, it was developed from the eighties, based in the assumptions of the Theory of species' evolution of Charles Darwin and the developments of neo-Darwinism and can be considered a synthesis of evolutionary biology and cognitive psychology (Barkow, Cosmides, & Tooby, 1992). Some important building blocks of evolutionary psychology are: modern developments in theoretical evolutionary biology the cognitive movement advances in paleoanthropology, hunter-gatherer studies and primatology research in animal behavior, linguistics, developmental psychology and neuropsychology.

The first building block offered theories on how natural selection acts on altruism, kinship, mating, cooperation, reproduction, parenting, risk taking, aggression etc. Modern adaptationism with concerns with the functional design of mechanisms given a recurrently structured ancestral world clarified how natural selection works, what counts as an adaptive function, and what are the criteria for calling a trait an adaptation.

The rise of computational sciences, information theory, cognitive psychology and advances in neurosciences, called sometimes the "cognitive revolution", provided a precise language for describing mental mechanisms as programs that process information (Barkow, Cosmides, & Tooby, 1992 Cosmides & Tooby, 2006 Seidl-de-Moura, 2005). Advances in paleoanthropology, hunter-gatherer studies and primatology provided data about the adaptive problems our ancestors had to solve to survive and reproduce and the environments in which they did so (Barkow, Cosmides, & Tooby, 1992 Cosmides & Tooby, 2006 Izar, in press).

Finally, a body of exciting research in animal behavior, linguistics, developmental psychology and neuropsychology showed that the mind is not a blank slate, passively recording the world. Human organisms come "equipped" with knowledge about the world, which allows them to learn some relationships easily and others only with great effort, if at all (Cosmides & Tooby, 2006).

The aim of EP is the mapping of our universal human nature, considered as the set of species specific information processing programs that have developed consistently in the human brain –the architecture of the human mind. As proposed by Cole,

EP presupposes that there is a universal human nature, but this universality exists basically in the level of psychological mechanisms developed by natural selection, and not in the expression of cultural behaviors (Cosmides, Tooby & Barkow, 1992). Those psychological mechanisms are adaptations to the way of life of hunter-gatherer of the Pleistocene and not necessarily to our modern circumstances and they were designed to solve the adaptative problems of our ancestors in this Environment of Evolutionary Adaptedness (EEA). They consist of emotions, preferences and propensities selected because they helped our ancestors to survive and reproduce in the past.

With those assumptions, mind is conceived as organized in specialized modules. Specialization was necessary for fast, economic and efficient input processing and execution of sophisticated tasks. EP acknowledges the multipurpose flexibility of human thought and action, but considers that it is caused by a cognitive architecture that contains a large number of evolved 'expert systems'.

An evolved psychological mechanism (EPM) is a set of inner processes that can solve specific problems of survival or reproduction during our evolutionary history. The evolved mechanism is designed by evolution to deal with a limited amount of information –it is highly sensitive to process input from a domain. This input tells an organism the type of adaptive problem it is facing and the evolved mechanisms transform it into output according to decisions rules. The output of an epm can be a behavior, or information that you can use and it is directed toward the solution to an adaptive problem. But it does not mean inflexibility of behavior. Evolutionary evolved mechanism is a theoretical construct to understand how the mind works. Evolutionary psychologists use the analogy with organs of the body (i.e. liver, lungs, heart, etc.) to illustrate that each one has a specific function. The heart is specialized for pumping blood and can not function for detoxifying poisons. The basic idea is that a similar principle could be used to understand how mind works. According to this, our minds consist of a large number of circuits that are functionally specialized.

Evolutionary evolved mechanism organize the way we interpret our experiences and provide universal frames of meaning that allow us to understand the actions and intentions of others. Human beings have some neural circuits whose design is specialized and the same mechanism is rarely capable of solving different adaptive problems. The function of the brain is to generate behavior that is sensitively contingent upon information from an organism's environment. It is, therefore, an information-processing device.

However, psychological mechanisms are not like rigid behaviors or instincts. They assume the form of decision rules, like "if something happens, then I can behave (or not) like that". Decision rules are grounded in specific contexts they permit several possible response options and can adapt themselves as an answer to differences in the environment. Only narrowly defined aspects of organisms fit together into functional systems: most ways of describing the system will not capture its functional properties. Not all behavior of an organism is adaptive.

The cognitive architecture is the joint product of genes and environment. The development of architecture of mind depends on a complex genetic and environmental interaction. It is a result of adaptations and must be considered as a process that will not stop. We continue to adapt to the different environments. In the theory of natural selection, as proposed by Darwin, there are three essential ingredients: variation, inheritance and selection. The adaptation, through natural selection, helps to solve problems of survival or reproduction and is based on inherited and reliably developing characteristics. Beside this, there are some by-products that do not solve adaptive problems but they happen to be coupled with adaptations. Furthermore, we cannot forget the random effects produced by forces such as change mutations.

The evolutionary scientists do not agree completely what in evolution belong to each category mentioned above and this is not our point. Despite some disagreements, and generally speaking, the question is that what we are consisted of a large collection of adaptations, and it could be perceived through behaviors, ways of react and think in certain situations very early in our lives.

Evolutionary psychology and child development

The application of the basic principles of the Theory of Evolution to explain the contemporary human development is denominated Evolutionary Developmental Psychology. It is a relatively new approach that has as purpose to investigate in what way our evolutionary past has influence about the ontogenetic development of human beings (Bjorklund & Pellegrini, 2002 Ellis & Bjorklund, 2005 Seidl-de-Moura, 2004).

There are two main assumptions that have heuristic contributions to the Developmental Psychology and that are related to evolutionary perspectives (Charlesworth, 1992). One of them is related with the individual differences and it is concerned to the physical and social environments. In this way, there are differences of children in relation to mortality, abuse, neglect, malnutrition, quality in child care and education. This condition can be related with the immediate effects on health, life and development of children and that have repercussions in the long-term survival and reproduction in adult life.

Other contribution is the notion of typical characteristics of the species. In the case of the human being would be the behaviors or the motivations that usually appear in different cultural and historical contexts (universal predispositions). They would appear because they have high adaptive value in other words, they are associated with the survival and perpetuation of our species. As a result of the long period of relative immaturity of human beings, it can be registered the following examples: parental care which includes attachment and conflict between child and adult, interaction between brothers, moral development training, structure and function of groups with children of similar ages, which involves domination, submission, competition and cooperation, learning, among others.

Although all those interaction systems are important, to the purpose of this paper we are going to present and to comment more specifically on one of them that is the relationship between adult-child. It is remarkable the child physical and psychological dependence on the adult due to the immaturity in the initial period of development.

Relationship between parental care and child development

The Evolutionary Theory suggests that parental behavior and degree of development of the offspring developed simultaneously, in philogenetic terms (Bjorklund & Pellegrini, 2000 Vieira & Prado, 2004). Thus, there is a balance between parental investment and initial state of development, as well as between the "effort in mating" (amount of time spent in seeking reproductive opportunities - mating) and "effort in the care of offspring" (all forms of care directed to progeny which carries an energetic cost to provide it – parental care). Parental investment subtracts energy available from another source, including a future pregnancy. In this way, such expenditure of energy in the development of young diminishes the effort in mating. Thus, how much is invested in mating versus parental care will vary between species and between females and males, depending on the characteristics of development of descents and ecological conditions present (Bjorklund & Yunger, 2002 Marlowe, 2000).

Among the mammals there is a wide variety of patterns of parental behavior, which can be classified according to the degree of development of the infant at birth (Rosenblatt, 1992). In some mammal species, the gestation period is short and offspring are born very premature. The thermo-regulatory and sensory systems are poorly developed and the infants are unable to feed themselves. Those species are called "altriciais" and include rodents, marsupials and primates. In those cases, parental care is of vital importance for the survival of offspring. On the other hand, there are species where the gestation period is long and the baby is born with vision, hearing, thermo-regulatory system and engine well developed (i.e. horses, cattle). These are called "precocial". In those cases, parental care is an important factor to the infant, although less crucial when compared with the previous group. The "altricial" model may be related to a marginal, floating, unstable environment, where the animals are living best when producing the most possible descendants. The standard "precocial" adapts itself better to tropical stable environments (Gould, 1999).

However, there are animals that do not fit into either of the two groups cited previously (Gould, 1999). The gestation period is long, the newborn has some skills that allow independence to perform some tasks, but depend on adults to others activities which are vital to their survival. For example, an animal that can be born with eyes open and with the hearing working well, but has no ability to move by itself and to follow the group in its moving around. Among these animals we can cite some species of primates (such as chimpanzees), including human beings. The latter has "precocial" characteristics for development, such as long life, large brain and small offspring, but they are quite defenseless as compared to the standard "altricial". The parental care of these animals is intense during the first moments of life, as they need to be fed and protected against predators and the climatic changes. The size of the brain is one of the characteristics that have made human babies to be born little developed, and in general, defenseless. The brain grows more slowly and during longer periods of time than in other primates. Furthermore, children characteristics during the early stages of development are attractive and act as triggers of parental responsiveness. For example, the vision of young babies is an activator of parental care. In addition, other features have evolved to this sense as the body size, orientation of the pelvis and the biped position and the position of the foramen magnum (the hole in the base of our skull from which starts the spine) that gives the orientation of the head and enables look forward when we are standing. This series of events over evolutionary time was given the name neotenia that is a process through which occurs the "retention of youth" or the retention of juvenile characteristics embryonic or a delay in development (Bjorklund, 1997).

With those considerations, one of the most important aspects of human development is the prolonged period of immaturity and dependency to adults, which is focused not only on the physical characteristics of the newborn, but have important implications in the way as individuals live as a species. Compared with other primates, humans take a disproportionate amount of time to reach reproductive maturity. Moreover, human beings spend more time with children than any other animal and Homo sapiens is the only species that continues to take care and feed their children until adolescence or later, which involves a high energetic cost (Bjorklund, 1997). The benefit associated with the high cost of a long period of immaturity may be a necessary contrivance for the effective learning of the complexities of human social community.

The slow development and the consequent physical and psychological dependence at birth require the presence of an adult to provide the conditions necessary for survival during that period. This is generally provided by the family, which may have different configurations. The parental human care and family formation are traces of co-evolution of different human characteristics, including those already mentioned like a lengthy period of childhood and adolescence, the brain size, high level of parental investment, and others such as: the hidden ovulation, not reproductive sexual activity and menopause (Geary & Flinn, 2001).

As mentioned previously, the reproductive effort made to find a partner and the investment to care of descendants evolved simultaneously. Specifically in the human case, this situation is related with differences in reproductive behavior and in the parental care expressed by men and women, because they had encountered various problems during evolutionary period (time, effort and resources to develop and produce offspring, for example). This situation had repercussion in producing different strategies to caring the descendants (Bjorklund & Pellegrini, 2000 Wittenberg & Tilson, 1980).

EP suggests that the expression of paternal investment is related, at least in some species, with the certainty of paternity to keep the proximity to the female (Geary, 2000). Furthermore, the lack of social support or father could increase the cost for mothers. The postpartum depression, according to Hagen (1999), would be an indicator of lack of social support, difficulties in providing the necessary resources to the baby during that period, or possible health problems related to the development of the newborn. Thus, the postpartum depression could be an adaptation that informs the mother that she is suffering or has suffered a cost which is too great, motivating her to reduce or eliminate the maternal investment in certain circumstances. This, on the other hand, provokes an increase of investment from other family members. However, is important to mention that these conditions can be an indicative of a situation of risk and not, necessarily, a determinant of the expression of the behavior of negligence in relation to the baby.

In sum, the central function of parental care and the human family, for authors who take the evolutionary perspective, is to promote an enabling environment for the development of complex social skills and, consequently, the child development and transformation of the child in an adult prepared to face the demands of adulthood life (Davis & Daly, 1997 Geary & Flinn, 2001). The context of human development – mainly provided by the family – involves many aspects which contribute to the development of various individual skills of the children.

Child development in cultural contexts

According to Blurton Jones (1993), parents in all cultures have three main purposes: 1) that their children survive, 2) that they become independent adults capable of supporting themselves and their family, 3) and that they become good members of society. However, ecological and socio-cultural conditions (context particularities) are important factors which modulate the form presented by the parental care system. One relevant concept to explain this variation is the "developmental niche" (Harkness & Super, 1996), a system composed by three subsystems: social and physical environment (such as type of housing, type of social organization of the family) shared customs and practices of childcare which are culturally and historically established (for example, the concept of childhood, relations between generations), and the psychology of caregivers (i.e. beliefs and expectations of mothers for children). These three sub-systems influence each other reciprocally.

The Parental Ethnotheories (PEthno) are part of the third subsystem of this model. They are implicit, difficult to observe and intrinsically connected with the other two subsystems. The PEthno are part of cultural models, which are considered a set of ideas, organized and shared by members of a cultural group, generally implicit and related into practice (Harkness et al., 2001 Suizzo, 2002).

In each culture people share values, ideas and beliefs about parenthood and child development, which include beliefs about how the children are and which are their needs, socialization goals and ideas on effective ways to raise children aiming those goals (Seidl-de-Moura et al., 2004). Evidences from the literature suggest that there are some connections between cultural beliefs about the nature of the child and the practices of care (Meléndez, 2005).

Parental knowledge about development encompasses beliefs about the basic needs and abilities of children, the most likely periods for acquisition of motor skills, cognitive and perceptual abilities beliefs about factors that may influence on the development beliefs about care of hygiene and safety that interfere with the health of children, among others (Ribas, Seidl-de-Moura & Bornstein, 2003 Seidl-de-Moura et al., 2004). Such systems beliefs about the development can guide parents' practices of caring for their children. For example, if they believe that the baby does not recognize human faces at birth, it is not likely that they will create many opportunities for face-to-face interaction. It has been reported differences in social and cultural beliefs about parental human development, relating to issues such as the socioeconomic status of caregivers (Ribas et al., 2003 Seidl-de-Moura et al., 2004).

The second important components of the PEthno are the socialization goals, or what the caregivers want and value for the future of their children. Those, as well as the knowledge of parents about the child development, also influence the practices of caregivers and vary in each cultural group. In general, studies carried out in contexts of more independent cultural orientation have found that mothers emphasized goals related to self-improvement and self-control of the child. In contrast, studies in more interdependent settings have noted the emphasis on proper demeanor of the child and his/her adaptation to social expectations (Keller, Borke, Yovsi, Lohaus & Jensen, 2005 Leyendecker, Harwood, Lamb & Schölmerich, 2002).

Beliefs about parenting practices of care are another dimension of parental cognition. Several studies are designed to specifically investigate that practices are more and less valued by parents of different cultures, social class, and education level, among others variables. There is evidence in the literature that the parental beliefs on practices of care vary with the cultural context (Keller, 2007 Keller et al., 2004 Keller et al., 2005 Keller et al, 2006 Suizzo, 2001).

Brazilian studies have been developed in different contexts in order to identify the importance attributed to different belief dimensions (Kobarg, 2006 Piovanotti, 2007 Ruela, 2006). The set of those studies have indicated the existence of diverse systems of beliefs between different Brazilians contexts, the influence of socio-demographic characteristics of the sample and, moreover, indicates possible changes in beliefs about parental practices of care over the years.

In another study conducted with 350 mothers of the all the five geographical regions of Brazil, it has been found that the size of the city and the educational level of mothers had influence on the mothers' socialization goals (Seidl-of-Moura, et al., in press). Complementing those results, a different analysis with the same group of mothers have indicated that there are shared beliefs about practices of care and that the mothers studied value most practices of proper presentation of their children and in second place their stimulation (Vieira et al., Submitted).

This paper aims to presenting the basis and some assumptions of EDP and to discuss some contributions of this theoretical perspective to the explanation child development. In light of current knowledge about development, and based on epistemological assumption that there should be links between biological factors, psychological and the external environment – including here the ecological context, social and cultural – it is considered that the EDP has scientific and social relevance because it broadens our vision on human development. However, as any other theoretical perspective, EDP has advantages and limitations. In the first case, contemporary perspectives in Psychology emphasize that the human baby is not a Tabula Rasa when born, but he/she is someone who has capacities, propensities for behavior that are characteristics of the species, motivation and needs. Human beings are also born with specific predispositions that may (or not) be confirmed by their ontogenetic history. Moreover, although there are different forms of physical organization, social and cultural environment in which children live, it is important to emphasize the need to know about our evolutionary past. This knowledge can help us not only to understand development, but also to create more adequate daily settings for child development. For example, although today there are different family configurations, it is necessary to understand that children at the early stages of their development need someone who could be an attachment figure. Depending on the roles they play in this context, father and mother, for example, among other primary caregivers, may develop different skills in caring for children. During our evolutionary history, mothers have specialized in caring for their descents by physical characteristics (pregnancy and childbirth, among others) and social and cultural traditions. However, the past does not determine the future, but may influence it and nowadays, the role of the father is increasingly valued. Knowing the evolutionary history does not mean that it determines our contemporary behavior and practices. The father can and should participate in the care of children. For this, it is necessary to create conditions in which this activity occurs, for example, to intensify the contact between fathers and their sons or daughters. Some activities may be more pleasant or easy to the father to do than others, such as playing with the child and taking it for walks. Others may require more learning, for example, direct care (nutrition and hygiene). In this way, is necessary also to know the ideas and values which are established by the cultural group (parental ethnotheories). The cognitive dimensions also are important components which have strong influence on the child development. The great challenge to Development Psychology is to integrate the different dimension related to the psychological development (behavior, culture, psychology, social context and biology).

Another implication of EDP is the knowledge that the research can bring about children and their development, recognizing the specific nature of ontogenetic adaptation, and expanding the consideration of the variables that interfere in the contexts of child development. In this sense, EDP can help to improve the assessment of risk and protection factors, making it possible to create or modify conditions in order to provide children with a better environment for their integral development.

Specifically in the case of the limitations of EDP, we can think of the difficulty in working with individual differences, because one of the purposes is to work with typical characteristics of the species. However, it is important to emphasize that the assumption adopted by EDP that there is a universal human nature does not cancel individual differences. As highlighted by Keller (2007) there are universal tasks of development, such as self development, which is modulated by the physical environment, social and cultural of the child.

The evolutionary perspective does not reduce human beings to its evolutionary history, but allows us to see our species through a broader perspective and have a better understanding of what it means to be human. Furthermore, although one of purposes of human beings is the survival and reproduction, with the consequence of species' perpetuation (product), it is necessary to understand the way to reach the maturity (process). In this way, one of the privileged areas in this context is the study of human development, which involves different level of analysis, such as biological, psychological, cultural and social context ones.

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It's No Delusion: Evolution May Favor Schizophrenia Genes

Dorus co-authored a report, appearing in this week's Proceedings of the Royal Society B, about the evolution of genes linked to schizophrenia. After analyzing human DNA from several populations around the world and examining primate genomes dating back to the shared ancestor of both humans and chimpanzees, researchers reached a striking conclusion that several gene variants linked to schizophrenia were actually positively selected and remained largely unchanged over time, suggesting that there was some advantage to having them.

"Schizophrenia can be explained by a lot of individual alleles (variations of genes)," Dorus notes. "There are many different loci that impact the actual manifestation of the disease." Over the past decade, several dozen genes have been identified as potential culprits, and scientists believe that several genes cause disruptions in protein formations predisposing a person to schizophrenia.

For this study, the team, which also included Bernard Crespi, an evolutionary biology professor at Simon Fraser University in British Columbia, and East Carolina University evolution professor Kyle Summers, focused on 76 gene variations most strongly related to schizophrenia. By comparing these combinations with the evolution of other genes known to affect neuronal processes, the researchers determined that 28 of the schizophrenia-associated genes have been evolutionarily preferred in recent years by either Caucasian, Asian or African populations.

"Because it's a such a complex genetic trait … you actually expect there to be some variability from population to population, in terms of what genes are playing a role in the disorder," Dorus says. He notes that he was surprised that the study turned up a positive selection for some of the genes most closely associated to the disease, including DISC1 (disrupted in schizophrenia 1), which is involved in the transport of proteins along the relatively lengthy cell bodies of neurons, among them. "The most important thing is we don't really know what the basis of the selection has been," he says. "It could be due to an entire range of neurodevelopmental processes."

Co-author Crespi says that a number of theories have been floating around regarding the persistence of schizophrenia's genetic underpinnings. One holds that schizophrenia is a "disorder of language" and that the illness is an unfortunate consequence of the development of human speech, expression and creativity. "Whenever you get strong selection, it's like a big plus, and you can drag along a lot of minuses," he says. "You can think of schizophrenics as paying the price of all the cognitive and language skills that humans have&mdashthey have too many of the alleles that taken individually…might have positive effect, but together they are bad."

Dorus says the team will now home in on the 28 genes fingered in positive selection in the hope of finding new treatments for the mysterious disorder.


John Maynard Smith: The Evolutionary Stable Strategy

John Maynard Smith is best known for his use of mathematical analyses in biology. Trained as an engineer and then as a biologist, Smith applied game theory to animal behavior and found that although variation exists, natural selection tends to maintain a balance between different characteristics within a species. This balance is called the "evolutionary stable strategy."

Credits: Courtesy of Anita Corbin and John O'Grady

Topics Covered:
Evolution Since Darwin

To noted evolutionary biologist John Maynard Smith, life is essentially about information -- how information is stored, passed on, and used by organisms as they live and reproduce. "And evolutionary theory is about how that information got there in the first place," he says.

In probing evolution from this point of view, Smith has employed mathematical tools, including what is called "game theory," to explain and predict evolutionary behavior. Originally developed by John von Neumann to study poker, chess, and other games, game theory analyzes complex situations in which the best strategy of one player depends on the actions of another.

But Smith, a professor at the University of Sussex, England, since 1965, is no dry theoretician. "I was a naturalist as a kid and have been ever since," he says, claiming an interest in everything from birds to bacteria.

Smith's best known work incorporated game theory into the study of how natural selection acts on different kinds of behavior. The old idea had been that selection inevitably favors organisms to act aggressively. Smith showed that this isn't necessarily true, and that selection may actually favor both aggressive and non-aggressive behaviors.

As an example, imagine that two populations, one of them aggressive (hawks) and one passive (doves). Hawks will always battle their neighbors over any resource. Doves won't fight under any circumstances. A population made up entirely of doves would be unstable that is, if a mutation caused the introduction of a single hawk, it would have an immediate advantage, and the hawkish behavior would bully the doves out of existence.

But a hawks-only population would also be unstable. A single dove introduced by mutation would have a long-term advantage. That's because the hawks' constantly aggressive behavior leads to frequent injury, while the dove, refusing to fight, escapes that risk.

Through application of game theory, Smith showed that there is a particular ratio of hawks to doves that forms what he called an "evolutionary stable strategy" for the species. Thus, selection actually works to maintain a balance of different characteristics in the population.


The evolution of earthworms

The humble earthworm might not seem the most exciting of animals. However, as Aristotle and Darwin stressed, their importance to the natural world is immense. New research, published this week in BMC Evolutionary Biology, provides the most comprehensive evolutionary history yet of the origins of the 6000+ species of earthworm. Lead authors Frank Anderson and Samuel James tell us more.

The plough is one of the most ancient and most valuable of man’s inventions but long before he existed the land was in fact regularly ploughed, and still continues to be thus ploughed by earth-worms. It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organised creatures.

Charles Darwin, The formation of vegetable mould through the actions of worms, with observations on their habits, pg. 313

The earthworms digging about in your back yard are members of a large, ubiquitous group with a deep evolutionary history. There are over 6000 earthworm species, found on all continents except Antarctica. Most earthworms dwell in soil, but many live in leaf litter, decaying logs and riverbanks, while some live in trees and even along the seashore.

Earthworms are major terrestrial ecosystem engineers and their economic impact is immense—earthworms turn over, aerate and drain soils, providing crucial assistance to farmers and gardeners, and compost-dwelling species are used to process food waste and animal manures. Aristotle recognized their importance as the “Intestines of the Earth”, and their reputation was burnished by Charles Darwin in The Formation of Vegetable Mould through the Action of Worms. On the other hand, a Chinese sage said “watch the earthworm, miss the eclipse”, implying that there are better things to observe. We might disagree, especially in the cases of bioluminescent earthworms, one of which (Avelona ligra) was sampled for this project, wildly colored earthworms (e.g., Archipheretima spp.), and those capable of remarkable feats of climbing, some found 40 meters up in French Guyana rainforests.

Despite their value, earthworms are generally ignored until they are needed for bait or become a problem. Approximately one-third of the earthworm species in North America have been introduced from Europe or Asia. Some have been introduced into northern forests, which have been free from earthworms since the end of the last ice age

11,000 years ago. Many other species in these forests rely on a deep layer of decaying leaf material, and earthworms are uniquely adapted to disturb this material.

Although earthworms are among the most familiar and economically important groups of large invertebrates, their evolutionary history is not well understood. As part of a collaborative effort funded by the US National Science Foundation to study annelid phylogeny, we harnessed high-throughput DNA sequencing to generate transcriptomes for representatives of nearly all of the eighteen living earthworm families as well as several groups thought to be closely related to them and used these data to infer phylogenetic relationships.

We found that the earthworm tree of life consists of two major branches, both with subgroups in the Northern and Southern Hemispheres. One of these branches includes at least three families, two found in eastern North America and one in Madagascar. The other branch contains the vast majority of earthworm species—the northern subgroup includes Lumbricidae, comprising nearly all familiar European species, and the southern subgroup includes Megascolecoidea (a group represented on all southern landmasses plus much of North America), two large Neotropical families and a tropical African family.

One long-standing question is whether the broad geographic distribution of earthworms is due to dispersal between continents (e.g., by rafting) or vicariance—riding the continents as they’ve drifted over several hundred million years—or a combination of these processes. We can use our phylogeny to assess the relative importance of these competing mechanisms, but to do so, we had to calibrate our phylogeny to the geological time scale.

Earthworms have left an impressive record of trace fossils, but it is difficult to determine which species made a particular set of fossilized burrows, since body fossils are extremely rare. However, earthworms and their relatives lay their eggs in cocoons, and sometimes these cocoons fossilize. Leech cocoon fossils are known from the late Triassic, 201 million years ago, which tells us not only the minimum age of leeches, but also the minimum age of the common ancestor of leeches and earthworms. We were able to use these fossils to calibrate our phylogeny and infer divergence dates.

Our analyses reveal that the ancestor of all living earthworms probably lived over 209 million years ago, making earthworms about as old as mammals and dinosaurs. Our date estimates for the divergences between the Northern and Southern Hemisphere subgroups of the two major branches of earthworms fall between 178-186 million years ago, coinciding with the breakup of the supercontinent Pangaea 180-200 million years ago and corroborating the hypothesis that continental breakup influenced early earthworm diversification. This also implies that earthworms likely inhabited Antarctica before the continent’s southward drift made it inimical to most terrestrial animal life.

Our phylogeny also provides a robust framework for investigating several questions about earthworm evolution. At several points in the phylogeny, earthworms have transitioned from terrestrial to aquatic habitats and vice versa. Most species in Clitellata (the group that includes earthworms) are aquatic, so earthworm genomes may retain ancestral genes that enable transitions between habitats. Alternatively, certain features may have been reinvented at each habitat transition. We have begun to explore this question, and hope to investigate other aspects of earthworm gene and genome evolution in our future work.


Watch the video: What would happen if you didnt drink water? - Mia Nacamulli (October 2022).