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Biological & Evolutionary Reasons for Palm (Bi)Symmetry

Biological & Evolutionary Reasons for Palm (Bi)Symmetry


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The fingers of the human palm exhibit a (bi)symmetrical pattern with regards to their size, in the sense that the thumb and the pinky are almost the same size, and the same holds for the index and ring finger. I was wondering what the biological imperatives and/or evolutionary advantages behind this physical characteristic are.

The only rationale I personally am able to come up with is that this particular arrangement might be optimal or ideal for grasping, handling, and manipulating objects, but am unsure of its truthfulness, and, even if correct, I would still be interested in exploring other possible avenues.


Bilateral Symmetry

Bilateral symmetry refers to organisms with body shapes that are mirror images along a midline called the sagittal plane. The internal organs, however, are not necessarily distributed symmetrically.

The vast majority of animals display bilateral symmetry also known as plane symmetry, this is a trait that applies to 99% of all animals, in the majority of phyla: Chordata, Annelida, Arthropoda, Platyzoa, Nematoda, and most Mollusca.

On the other hand, the Cnidaria display radial symmetry and the Porifera exhibit no symmetry.
The Echinodermata are unique, in that they display bilateral symmetry in their larval stage, and a special form of fivefold radial symmetry, pentamerism in their adult life stage.

Bilaterally symmetrical animals have a dorsal side (top), a ventral side (bottom) and distinct left and right sides. They also have an anterior side (head), and a posterior side (tail), and exhibit cephalization. Cephalization is the clustering of sensory organs at the anterior a body plan that arose because animals use forward motion, and so this end is the first to encounter the environmental stimuli to which an organism must react. The bilateral body plan may also be advantageous because it permits organisms to be more streamline. This would have been particularly important for ancestral organisms, which moved through the oceans.

To determine whether an animal has bilateral symmetry, it is possible to draw an imaginary (or real!) line down the center from its tip to the end a bilaterally symmetrical animal will have two sides which are near identical, albeit a mirror image.


New Theory on Why Men Love Breasts

Why do straight men devote so much headspace to those big, bulbous bags of fat drooping from women's chests? Scientists have never satisfactorily explained men's curious breast fixation, but theorists are gonna theorize. So let's take a tour of the sexy speculation surrounding the human bosom — with a few stops to explain why it's so hard to figure out just why breasts hold such allure.

Mammary glands are a defining feature of mammals, but humans seem unique in granting mammaries a large sexual role. That's not to say interest in nipples is entirely unheard of elsewhere in the animal kingdom: In the book "Biological Exuberance: Animal Homosexuality and Natural Diversity" (Stonewall Inn Editions, 1999), Canadian biologist Bruce Bagemihl notes that a couple of primate species, including humanity's close relative the bonobo, have been seen stimulating their own nipples while masturbating. Still, few mammals other than humans mate face-to-face (the behavior makes headlines when seen in the wild), so nipple stimulation isn't generally part of the script.

Researchers have long speculated that humans evolved the fatty deposits around the female mammary glands for sexual reasons. Anthropologist Owen Lovejoy argued that evolution put a bull's-eye around both female and male reproductive organs in order to promote pair bonding. In this hypothesis, it wasn't just the female breast that got a lift men acquired relatively large penises for their body size, too. [Why Do Women Have Breasts?]

Another long-standing theory holds that breasts evolved as a way to signal to men that the woman attached to them was nutritionally advantaged and youthful — and thus, a promising mate. Studies finding that men prefer large breasts and a high waist-to-hip ratio bolster the notion that an hourglass shape communicates youth and fertility. A 2004 study in the Proceedings of the Royal Society B even found that women with large breasts have higher levels of the hormone estradiol mid-cycle, which could increase fertility.

Nature or nurture?

But there are pitfalls to this line of work. For one thing, it's not actually clear that breasts are universally adored. In a 1951 study of 191 cultures, anthropologist Clellan Ford and ethologist Frank Beach reported that breasts were considered sexually important to men in 13 of those cultures. Of those, nine cultures preferred large breasts. Two — the Azande and Ganda of Africa — found long, pendulous breasts most attractive. Another two — the Maasai of Africa and Manus of the South Pacific — liked breasts that were upright and "hemispherical," but not necessarily large. Thirteen cultures also reported breast simulation during sex, but only three of those overlapped with the societies where men reported finding breasts important for sexual attraction.

In a chapter in the book "Breastfeeding: Biocultural Perspectives" (Aldine de Gruyter, 1995), cultural anthropologist Katherine Dettwyler describes telling friends in Mali about sexual foreplay involving breasts and getting responses ranging from "bemused to horrified."

"In any case, they regarded it as unnatural, perverted behavior, and found it difficult to believe that men would become sexually aroused by women's breasts, or that women would find such activities pleasurable," Dettwyler wrote.

In the cultural view, men aren't so much biologically drawn to breasts as trained from an early age to find them erotic.

"Obviously, humans can learn to view breasts as sexually attractive. We can learn to prefer long, pendulous breasts, or upright, hemispherical breasts. We can learn to prefer large breasts," Dettwyler wrote. [The 7 Biggest Mysteries of the Human Body]

Even if there is some biological underpinning for an interest in bosoms, it might vary by culture. A 2011 study compared men's preferences for breast size, symmetry, and areola size and color in Papua New Guina, Samoa and New Zealand and found that men from Papua New Guinea preferred larger breasts than men from the other two islands. Because the men surveyed from Papua New Guinea hailed from more of a subsistence culture than the men in Samoa or New Zealand, the results support the idea that in places of scarcity, padded bustlines could signal a well-fed woman with reserves for pregnancy and childrearing, the researchers wrote. Areola size and color preferences were highly idiosyncratic between cultures.

Sexual sideshow?

The main job of breasts, of course, is to feed offspring. Some researchers think that sexual interest in breasts simply hijacks the breastfeeding circuitry and uses it for another purpose.

Larry Young, a professor of psychiatry at Emory University who studies the neurological basis of complex social behaviors, thinks human evolution has harnessed an ancient neural circuit that originally evolved to strengthen the mother-infant bond during breastfeeding, and now uses this brain circuitry to strengthen the bond between couples as well. The result? Men, like babies, love breasts.

When a woman's nipples are stimulated during breastfeeding, the neurochemical oxytocin, otherwise known as the "love drug," floods her brain, helping to focus her attention and affection on her baby. But research over the past few years has shown that in humans, this circuitry isn't reserved exclusively for infants. [The Cleavage Countdown: 8 Facts About Breasts]

Recent studies have found that nipple stimulation enhances sexual arousal in the great majority of women, and it activates the same brain areas as vaginal and clitoral stimulation. When a sexual partner touches, massages or nibbles a woman's breasts, Young said, this triggers the release of oxytocin in the woman's brain, just like what happens when a baby nurses. But in this context, the oxytocin focuses the woman's attention on her sexual partner, strengthening her desire to bond with this person.

In other words, men can make themselves more desirable by stimulating a woman's breasts during foreplay and sex. Evolution has, in a sense, made men want to do this. According to Young, the theory "just makes a lot of sense." Young elaborated on the theory in his book, "The Chemistry Between Us" (Current Hardcover, 2012), co-authored by Brian Alexander.

Attraction to breasts "is a brain organization effect that occurs in straight males when they go through puberty," Young told Live Science. "Evolution has selected for this brain organization in men that makes them attracted to the breasts in a sexual context, because the outcome is that it activates the female bonding circuit, making women feel more bonded with him. It's a behavior that males have evolved in order to stimulate the female's maternal bonding circuitry." [Why Do Men Have Nipples]

So, why did this evolutionary change happen in humans, and not in other breastfeeding mammals? Young thinks it's because we form monogamous relationships, whereas 97 percent of mammals do not. "Secondly, it might have to do with the fact that we are upright and have face-to-face sex, which provides more opportunity for nipple stimulation during sex. In monogamous voles, for example, the nipples are hanging toward the ground and the voles mate from behind, so this didn't evolve," he said. "So, maybe the nature of our sexuality has allowed greater access to the breasts."

Young said competing theories of men's breast fixation don't stand up to scrutiny. For example, the argument that men tend to select full-breasted women because they think these women's breast fat will make them better at nourishing babies falls short when one considers that "sperm is cheap" compared with eggs, and men don't need to be choosy.

But like any evolutionary explanation for breasts, Young's theory runs into cultural controversy.

"Always important whenever evolutionary biologists suggest a universal reason for a behavior and emotion: how about the cultural differences?" Rutgers University anthropologist Fran Mascia-Lees wrote in an email to Live Science.

Young responded that there are not enough studies looking at breast stimulation during foreplay across cultures to rule out the importance of the nipple-oxytocin bonding loop. Notably, men often like nipple stimulation, too. A 2006 study published in the Journal of Sexual Medicine found that in a sample of undergraduate men in the United Kingdom, 51.7 percent found nipple stimulation arousing. About 82 percent of women said the same. Male nipples are a vestige of prenatal development in men, but they are hooked up to nerves and blood vessels, just like female nipples.

However, less is known about the innervation of nipples in men, studies on how nipple stimulation contributes to their sexual arousal are lacking, the researchers wrote. Perhaps the real quandary isn't why the female breast is so fetishized, but why we don't ask more questions about what's on men's chests.

Editor's Note: This article was first published on Sept. 26, 2012 it was updated to include more research and information on theories behind men's love of breasts.


Arecaceae: Characters, Distribution and Types

Mainly trees with stout unbranched stem ending in crown of leaves leaves large, compound, alternate, young leaves are plicate, exstipulate with long petioles inflorescence enclosed in a persistent spathe flowers unisexual perianth 6 in two whorls of 3 each in male flower 6 stamens in two whorls, anthers versatile in female flowers carpels three apocarpous or syncarpous, superior, trilocular or rarely unilocular fruit berry or drupe seed endospermic.

A. Vegetative characters:

Large unbranched trees (Phoenix, Areca catechu), shrubs or garden palms, trailing (Calamus), herbs (Reinhardtia).

Adventitious roots arising from the base of bulbous stem. Thick aerial roots are also found in some species of Manicaria.

Aerial, woody, erect, unbranched, very rarely branched, (Hyphaene), in some short rhizome (Nipa), cylindrical, hairy, old stem protected by woody leaf bases, climbing (Calamus).

Alternate crowded at the apex of stem giving palmlike appearance to the plant petiolate, leaf-base sheathing, broad and persistent exstipulate, compound pinnately (Phoenix, Areca), palmately (Borassus), acute, thick, leathery, parallel venation. In some palms (Copernica) the petiole is prolonged into a ligule like structure called histula.

B. Floral characters:

It is simple or compound, spike or branched panicle, usually a spadix with a woody spathe which opens by two valves spadix may have sessile or pedicellate flowers, simple racemose (Borassus), or compound racemose (Cocos) or even profusely branched panicle (Daemonorops).

Sessile or shortly pedicellate, bracteate, mostly unisexual (Phoenix) or hermaphrodite (Livingstonia), actinomorphic, incomplete or complete, hypogynous trimerous, flowers are of small size and produced in large numbers. Plant may be monoecious or dioecious.

In monoecious flower the position of male and female flowers is variable i.e. male flowers at the base or at the apex and the female flowers at the upper part (Ruffia, Rap his) or male and female flowers are inter-mingled or female flowers in the centre, made on the either side as the Cocos, Caryota.

Tepals 6, in two whorls of 3 each, polyphyllous or slightly connate at the base perianth lobes tough, persistent, coriaceous, leathery or fleshy, valvate or imbricate aestivation, white or petaloid.

In male or hermaphrodite flowers, stamens are 6 in number, two whorls of 3 each, polyandrous, staminodes may be present in the female flowers anthers versatile, dithecous, basifixed or dorsifixed, introrse, filament short and distinct.

In female or hermaphrodite flower-carpels 3 in number, apocarpous or syncarpous, ovary superior, trilocular, axile placentation, single ovule in each loculus style short, stigma small or broad or 3 lobed.

Usually a berry, fleshy or fibrous waxy coating on the fruit the mature fruit contains a single seed (Phoenix) drupe (Cocos nucifera).

Anemophilous or entomophilous.

Distribution of Arecaceae:

The family is commonly known as “Palm family”. It includes 217 genera and 2500 species. The members are confined to tropics in both the hemispheres and extending in the warmer regions of the world. In India it is represented by 225 species belonging to 25 genera.

Economic Importance of Arecaceae:

Pith of Metroxylon rumphii and M. leave (Sago palm) yield sago of commerce. The sap of Borassus yields a sugar, which on fermentation gives alcoholic drink “Toddy”. Fruits of Phoenix dactylifera are very delicious and eaten throughout the Arab world. The nuts of Areca catechu serve as a asteringent and used with betel leaves. The milk of Cocos nucifera makes a refreshing drink, endosperm is eaten raw and stored when dry.

Tender leaves of Calamus travancoricus are given in bilousness, worms and dyspepsia.

Mesocarps of the drupes of Coconut are extensively used for stuffing pillows and sofa sets. The cane of commerce is obtained from Calamus tenuis and C. rotang and are used for making mats, baskets and other furniture.

Borassus flabellifer – yields palmyra fibres which are used to prepare brushes and brooms. The leaves are used in the manufacture of hand fans, umbrellas, baskets and mats.

Wax is obtained from the leaves of Copernicia cerifera and Ceroxylon andicola. The wax is used in making gramophone records, candles and models.

Coconut oil is obtained from the Cocos nucifera and is used as hair oil, in soap industry and also for cooking.

Roystonea regia (Royal palm), Corypha elata (Talipot palm).

Primitive characters:

1. Mostly plants are trees.

2. Leaves are spirally arranged.

3. Flowers are actinomorphic, hypogynous and hermaphrodite.

4. Gynoecium is apocarpous (Phoenix, Rhapis).

Advanced characters:

1. Small herbaceous forms are also present.

2. Leaves are compound and exstipulate.

3. Inflorescence is a spadix.

5. Flowers are usually unisexual (Phoenix, Cocos).

8. Gynoecium tricarpellary, syncarpous rarely unilocular.

9. Style very short or absent.

According to Eames (1961) “The palms give evidence of great age they are primitive taxon that has become greatly diversified and advanced in many characters, each character giving evidence of long specialization.”

Affinities of Arecaceae:

Rendle placed the family together with the Araceae under Spadiciflorae due to unisexual flowers and occurrence of spadix.

Hutchinson (1959) traces the origin of Palms from Liliflorean stock directly from Liliaceae through Dracaena-Cordyline. Erdtman also reports similar pollen structure of Palms and Dracaena.

Palmaceae is closely related to Liliaceae in palm-like habit of Yucca, Dracaena of Liliaceae, perianth segments, stamens in two whorls, tricarpellary, syncarpous ovary, and structure of pollen grains (Dracaena).

Common plants of the family:

1. Areca catechu (H. Supari Betelnut palm): Graceful single stemmed palm.

2. Caryota urens (Fish-tail palm): Toddy is tapped from its stem.

3. Corypha umbraculifera (Talipot palm): Planted in gardens.

4. Cocos nucifera (H. Nariyal): a tall palm, widespread along sea shore in tropics and sub-tropics.

5. Calamus tenuis and C. rotang (H. Bent): climbing palm.

6. Metroxylon: Fruits take 3 years to mature and pith yields ‘sago’.

7. Nipa fruitcans (Water coconut): palm with delicate round leaves used as cigarette paper stemless palm of Sunderbans.

8. Phoenix dactylifera (Date palm): tall palm with rough trunk due to persistent leaf bases fruits are delicious.

Division of the family and chief genera:

The family Arecaceae is divided into seven tribes as follows:

Leaves pinnatisect flowers hermaphrodite fruit a berry or fibrous drupe e.g. Areca.

Leaves pinnatisect flowers unisexual, e.g. Borassus.

Leaves pinnatisect flowers hermaphrodite, fruit fibrous drupe not covered with scales e.g. Cocos.

Leaves pinnatisect flowers unisexual fruit one seeded berry e.g. Phoenix.

Tribe 5. Phytelephanteae:

Leaves pinnatisect male and female inflorescences separate e.g. Nipa.

Tribe 6. Lepidocaryeae:

Leaves palmatisect or pinnatisect spadices terminal or interfoliar e.g. Calamus.

Leaves palmatisect flowers unisexual or bisexual, e.g. Corypha.

Important Type of Arecaceae:

Phoenix sylvestris (Date palm) (Fig. 111.2):

Aerial, woody, erect, cylindrical, rough, covered with persistent leaf bases, unbranched, solid, brown.

Forming a dense terminal crown, exstipulate, compound, unipinnate, petiolate, glabrous.

Sub-sessile, lanceolate, entire, acute, unicostate parallel venation.

Spadix-branched, erect, long, enclosed by spathe.

Small, actinomorphic, hypogynous, unisexual, bracteate, incomplete.

Bracteate, sessile, incomplete, numerous, angular, actinomorphic, hypogynous, trimerous.

Tepals 6, in two whorls of 3 each, white, angular, free and inferior.

Stamens 6, in two whorls of 3 each, polyandrous, filament short anthers dithecous, dorsifixed, introrse.

Bracteate, sessile, incomplete, actinomorphic, hypogynous, trimerous.

Tricarpellary, syncarpous, ovary superior, one ovule in each carpel style absent stigma hooked.


5 Main Types of Symmetry Seen in Animals

The following points highlight the five main types of symmetry seen in animals. The types are: 1. Asymmetrical Symmetry 2. Spherical Symmetry 3. Radial Symmetry 4. Biradial Symmetry 5. Bilateral Symmetry.

Type # 1. Asymmetrical Symmetry:

In some animals there are no body axis and no plane of symmetry, hence the animals are called asymmetrical. The amoeboid forms (e.g., Amoeba) and many sponges have ir­regular growth pattern of the body and can­not be divided into two equal halves (Fig. 9.1).

Type # 2. Spherical Symmetry:

In spherical symmetry the shape of the body is spherical and lack any axis. The body can be divided into two identical halves in any plane that runs through the organism’s cen­tre. In asymmetrical symmetry and spherical symmetry the polarity does not exist and spherical symmetry is seen in radiolarian protozoa (Fig. 9.2).

Type # 3. Radial Symmetry:

In radial symmetry the body can be divided into two roughly equal halves by any one of many vertical planes passing through the central axis (Fig. 9.3A-C) like the spokes of a wheel. The animals which exhibit prima­rily radial symmetry are cylinder in form and the similar parts of the body are arranged equally around the axis. The axis extends from the centre of the mouth to the centre of the aboral side.

The radial symmetry is seen among the sessile and sedentary animals such as in some sponges, hydroids, anthozoan pol­yps, medusae and sea stars.

Special forms of radial symmetry are observed in different groups of animals such as:

(i) Tetramerous symmetry:

Many jelly fishes possess 4 radial canals and the body can be divided into 4 equal parts. Hence the ani­mals exhibit tetramerous raidal symmetry (Fig. 9.3B).

(ii) Pentamerous symmetry:

Most echinoderms possess pentamerous radial symme­try because the body can be divided into 5 roughly equal parts (Fig. 20.1). The body parts are arranged around the axis of the mouth at orientations of 72° apart. The larvae of echinoderms are bilaterally symmetrical but acquires radial symmetry in adult stage. The radial symmetry of echinoderms is regarded as a secondary acquisition.

(iii) Hexamerous symmetry:

The sea anemo­nes and true coral polyps belong to the sub­class Hexacorallia (class Anthozoa). The mesenteries and tentacles are arranged in the multiple of six. The mesenteries are usually paired and are arranged in the multiple of six. The body of hexacorallian polyps exhib­its hexameric plan and have sixfold internal symmetry.

(iv) Octomerous symmetry:

The body of octocorallian polyps (subclass Octocorallia) shows octomeric radial symmetry and con­tains 8 hollow marginal tentacles and 8 mesenteries and the body can be divided into 8 equal parts (Fig. 9.3C).

The animals with radial symmetry do not have anterior and posterior sides or dorsal and ventral surfaces. They have a mouth bear­ing oral side and the side away from the mouth called the aboral side.

Type # 4. Biradial Symmetry:

The body of animals which exhibits biradial symmetry, represents a combination of both radial and bilateral symmetry. The organs are arranged radially and the body can be divided into two by a mid-longitudinal plane. Ctenophores exhibit biradial symmetry.

Type # 5. Bilateral Symmetry:

In bilateral symmetry the body parts are arranged in such a way that the animal is divisible into roughly mirror image halves through one plane (mid sagittal plane) only (Fig. 9.4A). This plane passes through the axis of the body to separate the two halves which are referred to as the right and left halves.

The animals which exhibit bilateral symmetry called bilateria. Bilaterally sym­metrical animals include acoelomates, pseudo-coelomates and eucoelomates among invertebrates and both lower chordates and vertebrates.

The entire body of a bilateria can be divided into three planes such as— (i) frontal (ii) sagittal and (iii) transverse (Fig. 9.4). Any of the vertical planes perpen­dicular to the sagittal plane that passes through the body separating the upper and underside is called frontal plane.

The upper-side is also called dorsal which is usu­ally away from the ground and near the back of the animal. The underside is also called ventral which is usually facing towards ground. A longitudinal plane that passes along the axis of the body of bilaterally sym­metrical animal to separate right and left sides is called the mid- sagittal plane (Fig. 9.4B).

An imaginary plane that crosses the body, perpendicular to the mid sagittal plane called transverse plane. The body of bilateria has the term lateral (two sides of the body), anterior (the end which usually moves forward dur­ing movement and bears mouth) and poste­rior (Fig. 9.5) (the end opposite to anterior).

Advantages of Symmetry:

1. Bilateral symmetry is associated with the term cephalization—meaning the spe­cialization of the anterior end of the body to form the head where the nervous tissues, sense organs and feeding organs are concen­trated.

2. Other advantages of this symmetry are the streamlining of the body, development of different organs in different body regions and more efficient unidirectional movement.


Biology and Gender

Several biological explanations for gender roles exist, and we discuss two of the most important ones here. One explanation is from the related fields of sociobiology (see Chapter 2 “Eye on Society: Doing Sociological Research”) and evolutionary psychology (Workman & Reader, 2009) and argues an evolutionary basis for traditional gender roles.

Scholars advocating this view reason as follows (Barash, 2007 Thornhill & Palmer, 2000). In prehistoric societies, few social roles existed. A major role centered on relieving hunger by hunting or gathering food. The other major role centered on bearing and nursing children. Because only women could perform this role, they were also the primary caretakers for children for several years after birth. And because women were frequently pregnant, their roles as mothers confined them to the home for most of their adulthood. Meanwhile, men were better suited than women for hunting because they were stronger and quicker than women. In prehistoric societies, then, biology was indeed destiny: for biological reasons, men in effect worked outside the home (hunted), while women stayed at home with their children.

Evolutionary reasons also explain why men are more violent than women. In prehistoric times, men who were more willing to commit violence against and even kill other men would “win out” in the competition for female mates. They thus were more likely than less violent men to produce offspring, who would then carry these males’ genetic violent tendencies. By the same token, men who were prone to rape women were more likely to produce offspring, who would then carry these males’ “rape genes.” This early process guaranteed that rape tendencies would be biologically transmitted and thus provided a biological basis for the amount of rape that occurs today.

If the human race evolved along these lines, sociobiologists and evolutionary psychologists continue, natural selection favored those societies where men were stronger, braver, and more aggressive and where women were more fertile and nurturing. Such traits over the millennia became fairly instinctual, meaning that men’s and women’s biological natures evolved differently. Men became, by nature, more assertive, daring, and violent than women, and women are, by nature, more gentle, nurturing, and maternal than men. To the extent this is true, these scholars add, traditional gender roles for women and men make sense from an evolutionary standpoint, and attempts to change them go against the sexes’ biological natures. This in turn implies that existing gender inequality must continue because it is rooted in biology. As the title of a book presenting the evolutionary psychology argument summarizes this implication, “biology at work: rethinking sexual equality” (Browne, 2002).

According to some sociobiologists and evolutionary psychologists, today’s gender differences in strength and physical aggression are ultimately rooted in certain evolutionary processes that spanned millennia.

Vladimir Pustovit – Couple – CC BY 2.0.

Critics challenge the evolutionary explanation on several grounds (Hurley, 2007 Buller, 2006 Begley, 2009). First, much greater gender variation in behavior and attitudes existed in prehistoric times than the evolutionary explanation assumes. Second, even if biological differences did influence gender roles in prehistoric times, these differences are largely irrelevant in today’s world, in which, for example, physical strength is not necessary for survival. Third, human environments throughout the millennia have simply been too diverse to permit the simple, straightforward biological development that the evolutionary explanation assumes. Fourth, evolutionary arguments implicitly justify existing gender inequality by implying the need to confine women and men to their traditional roles.

Recent anthropological evidence also challenges the evolutionary argument that men’s tendency to commit violence, including rape, was biologically transmitted. This evidence instead finds that violent men have trouble finding female mates who would want them and that the female mates they find and the children they produce are often killed by rivals to the men. The recent evidence also finds those rapists’ children are often abandoned and then die. As one anthropologist summarizes the rape evidence, “The likelihood that rape is an evolved adaptation [is] extremely low. It just wouldn’t have made sense for men in the [prehistoric epoch] to use rape as a reproductive strategy, so the argument that it’s preprogrammed into us doesn’t hold up” (Begley, 2009, p. 54).

A second biological explanation for traditional gender roles centers on hormones and specifically on testosterone, the so-called male hormone. One of the most important differences between boys and girls and men and women in the United States and many other societies is their level of aggression. Simply put, males are much more physically aggressive than females and in the United States commit about 85%–90% of all violent crimes (see Chapter 7 “Deviance, Crime, and Social Control”). Why is this so? As Chapter 7 “Deviance, Crime, and Social Control” pointed out, this gender difference is often attributed to males’ higher levels of testosterone (Mazur, 2009).

To see whether testosterone does indeed raise aggression, researchers typically assess whether males with higher testosterone levels are more aggressive than those with lower testosterone levels. Several studies find that this is indeed the case. For example, a widely cited study of Vietnam-era male veterans found that those with higher levels of testosterone had engaged in more violent behavior (Booth & Osgood, 1993). However, this correlation does not necessarily mean that their testosterone increased their violence: as has been found in various animal species, it is also possible that their violence increased their testosterone. Because studies of human males can’t for ethical and practical reasons manipulate their testosterone levels, the exact meaning of the results from these testosterone-aggression studies must remain unclear, according to a review sponsored by the National Academy of Sciences (Miczek, Mirsky, Carey, DeBold, & Raine, 1994).

Another line of research on the biological basis for sex differences in aggression involves children, including some as young as ages 1 or 2, in various situations (Card, Stucky, Sawalani, & Little, 2008). They might be playing with each other, interacting with adults, or writing down solutions to hypothetical scenarios given to them by a researcher. In most of these studies, boys are more physically aggressive in thought or deed than girls, even at a very young age. Other studies are more experimental in nature. In one type of study, a toddler will be playing with a toy, only to have it removed by an adult. Boys typically tend to look angry and try to grab the toy back, while girls tend to just sit there and whimper. Because these gender differences in aggression are found at very young ages, researchers often say they must have some biological basis. However, critics of this line of research counter that even young children have already been socialized along gender lines (Begley, 2009 Eliot, 2009), a point to which we return later. To the extent this is true, gender differences in children’s aggression may simply reflect socialization and not biology.

In sum, biological evidence for gender differences certainly exists, but its interpretation remains very controversial. It must be weighed against the evidence, to which we next turn, of cultural variations in the experience of gender and of socialization differences by gender. One thing is clear: to the extent we accept biological explanations for gender, we imply that existing gender differences and gender inequality must continue to exist. This implication prompts many social scientists to be quite critical of the biological viewpoint. As Linda L. Lindsey (2011, p. 52) notes, “Biological arguments are consistently drawn upon to justify gender inequality and the continued oppression of women.” In contrast, cultural and social explanations of gender differences and gender inequality promise some hope for change. Let’s examine the evidence for these explanations.


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9. Being different

But sometimes, opposites do attract. For instance, if you've lived a sheltered life, you might gravitate towards people who have had extremely different experiences to you.

There may be some biological basis to opposites attracting, too. When it comes to reproduction, a bit of variety works in your favour. For instance, the major histocompatibility complex (MHC) is a part of the immune system that helps cells recognise foreign molecules. When the MHC is vastly different from your mate's, this decreases the danger of mating with someone you're related to, and increases the genetic variability of any offspring you have — meaning they're more likely to be healthier with a better immune system.


Structure bionic design method oriented to integration of biological advantages

Structure bionic optimization design is one kind of important lightweight design method. There are many high-specific-stiffness load-bearing topology structures in nature, whose mechanical properties and load-bearing mechanisms are quite different. These efficient load-bearing structures in nature provide important inspirations for structural bionic design. However, space topology structure of biology corresponds to its specific environment, which is more suitable for the specific load-bearing case. How to realize the complementary integration of biological advantages is an important problem in bionics research, which has not been solved effectively. Based on mapping inversion relationship (RMI) method and the matter-element (ME) theory, the structure bionic design method oriented to the integration of biological advantages is proposed. The proposed method applies the extensibility matter-element in an interdisciplinary way to solve this problem innovatively and effectively. Instead of random or wild mental stimulation, the proposed method formalizes the problem-solution for the integration of biological advantages. An example is used to show the concrete implementation process based on this method, and the results show the effectiveness of this proposed method. The proposed method could be extended to other bionic studies about biological advantages integration in further research.

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8 Conclusions and future work

Advancement in science and technology produces a massive volume of real networks in various fields. The analysis of these networks gives an insight into the corresponding systems and organisms. The overrepresented subgraphs in these networks, which are statistically significant, are called network motifs. Network motifs are the building blocks of networks and are often biologically significant, which makes the identification of the motifs extremely important. Network motif discovery has proved to be a computationally challenging task. There exist many tools and algorithms to discover network motifs. However, motif discovery capabilities can be improved further with new developments.

  1. The exponential increase of computational resources with respect to both graph and motif size for enumerating subgraphs prohibits tools and algorithms from dealing with large motifs.
  2. Solving an NP-complete problem for the subgraph isomorphism check is highly expensive.
  3. Determine the statistical significance of a candidate motif required repeated computations in a sufficient number of randomised networks.
  4. The challenges mentioned above increase further due to the continuous growth of real-world networks.
  1. Small motifs are the constituents of large motifs hence the small motifs can be used as a seed to search the large motifs. This idea can be used to design scalable algorithms for discovering large motifs.
  2. The number of redundant computations in the random networks can be reduced significantly by limiting the subgraph census only to a small set of potential motifs. Efficient data structures need to be developed to track the candidate motifs.
  3. Colour coding techniques can be applied to quickly find network motifs in the input network as well as random networks.
  4. Hybrid algorithms can be proposed by combining the efficient parts of two or more algorithms.
  5. Polynomial-time algorithms do exist for subgraph isomorphism check for special patterns. These distinctive patterns can be prioritised in the motif discovery process.
  6. Parallel algorithms can be implemented to decrease the runtime. Some existing algorithms have exploited only coarse grain parallelism. Efficient fine-grained parallelism is perhaps the most crucial improvement needed currently for network motif discovery that could simultaneously analyse different parts of the network, thus reducing the execution time and enabling our reach to larger motifs and networks.
  7. The future version of the tools most includes a user-friendly interface for better visualisation and analysis.
  8. The tools and algorithms most support a wide variety of input/output formats.
  9. Web tools are more convenient to use in comparison with installing the tool locally because the tools may require some resources which are not available in the local machine.


Watch the video: The science of symmetry - Colm Kelleher (September 2022).


Comments:

  1. Dylon

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  2. Shephard

    And all?

  3. Mazugal

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  4. Zadornin

    Yes, it's Teller story

  5. Cradawg

    That's one less worry! Good luck! Better!

  6. Hudak

    In my opinion you are wrong. Enter we'll discuss it.



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