All three rules seem to be exemplified in human evolution. Modern humans tend to be larger and rounder in cooler environments than in tropical environments. Over time, the human lineage has gotten larger … australopiths of the Miocene and Pliocene were smaller than Homo erectus and modern Homo sapiens. In comparing contemporary African modern humans and European Neanderthals, the latter are rounder and have shorter limbs, especially the distal parts of the limbs (forearms and the leg below the knees). In fact, this difference in body proportion is one of the key features that physical anthropologists use to distinguish between regular modern humans and Neanderthals when faced with that task.

Bunnies demonstrating Allen’s rule.

The usual assumption is that these changes in body form are selected for as a result of various environmental pressures, and that these features of body size and shape become adaptive features seen in particular populations. The body shape story is part of the Darwinian story of adaptation as well as, in some cases, the story of racial differentiation among humans or other organisms.

And of course, it is all wrong, as usual.

Well, OK, not all wrong, but certainly not as simple as one might think.

There is a paper just out in the Proceedings of the National Academy of Sciences that looks at body size proportions and Allen’s rule, and that presents (and summarizes from earlier work) some interesting results. But before we look at that, let’s make sure we are on the same page regarding the basic evolutionary models we are messing with here.

First, let’s dispense with Cope’s Rule because it really isn’t too important here. The presumption is that bigger is better in enough different ways … to avoid predators, to out compete conspecifics, whatever … that over time there is a trend to get bigger.

Bergmann’s rule — mammals get larger in cooler environments — is presumed to work because of the simple relationship between volume and surface area. Mammals, endothemeric creatures that they are, produce heat from their tissues (their volume) and lose it through their skin (their surface). As a a thing … a mammal, a balloon, a color television set, whatever … gets larger in size, the surface area goes up with a function approximated by a linear dimension squared, while the volume goes up with a function approximated by the same linear dimesion cubed. Volume grows faster than surface area, if shape is kept constant, when a thing gets bigger.

So, having more heat-engine (volume, tissue) compensates for the increased loss via the surface (skin) in cold climates. Bigness is good in cool climates, and conversely, smallness is good in warm climates.

But shape need not stay constant. An object shaped like a sphere will have minimal surface area compared to volume, while an object shaped like a chopstick will have lots of surface area per volume. Getting all lean and gangly is a tropical thing to do, getting all rotund and short-limbed is an arctic thing to do. That’s Allen’s Rule. Shortening the limbs, tail, and in some cases, ears gets the roundosity that the cool-climate mammal benefits from.

This rule-like patterning of body size and shape has been observed within species and among related species distributed across climatically diverse geographical areas, or over time. Bergmann’s rule has been observed in pack rats tracking climatic changes during the Pleistocene; Humans are said to vary in this matter, with tropical proportions being distinct from arctic proportions; rabbit species go from round short eared and short tailed forms to lanky long eared and long tailed forms, and so on.

But not all body size and shape effects that may in fact be tracking environmental clines are genetic. For instance, body size may be very much a function of diet and not genes, depending on the population.

The paper at hand examines Allen’s rule in this regard. From the abstract:

Allen’s Rule documents a century-old biological observation that strong positive correlations exist among latitude, ambient temperature, and limb length in mammals. Although genetic selection for thermoregulatory adaptation is frequently presumed to be the primary basis of this phenomenon, important but frequently overlooked research has shown that appendage outgrowth is also markedly influenced by environmental temperature. Alteration of limb blood flow via vasoconstriction/vasodilation is the current default hypothesis for this growth plasticity, but here we show that tissue perfusion does not fully account for differences in extremity elongation in mice. We show that peripheral tissue temperature closely reflects housing temperature in vivo, and we demonstrate that chondrocyte proliferation and extracellular matrix volume strongly correlate with tissue temperature in metatarsals cultured without vasculature in vitro. Taken together, these data suggest that vasomotor changes likely modulate extremity growth indirectly, via their effects on appendage temperature, rather than vascular nutrient delivery. When combined with classic evolutionary theory, especially genetic assimilation, these results provide a potentially comprehensive explanation of Allen’s Rule, and may substantially impact our understanding of phenotypic variation in living and extinct mammals, including humans.

In short, body proportions can be local non-genetic adaptations, or arise as a combination of genetic and ontogenetic causes. This paper further suggests that the non-genetic parts of the mechanism are different than previously thought.

The following photograph demonstrates the effect of enviornment on limb proportion. The researchers grew mice in very different temperatures, and low and behold, the mice grew up with different proportioned limbs.

The same effect is seen when little mouse bones are grown in vivo:

And here’s a graph showing the in vivo effects of cold, control, and warm grown metatarsals over two and four days. The colder the setting, the shorter the bone.

From the paper’s conclusion:

From an evolutionary perspective, Allen’s ”extremity size rule” may not actually reflect a functional genotypic adaptation in some or even many homeotherms (9, 10), but may instead be partially or wholly dependent on environmental temperature; that is, a secondary growth response to ”facultative extremity heterothermy” in mammals that maintain constant core body temperatures.

One would assume that significant differences in limb proportions between species that follow Allen’s rule are genetic, even if there is a phenotypic effect. I know of no widespread reports that tropical animals kept in temperate zoos or temperate or arctic animals raised in zoos in warmer climes show major body proportion shifts. On the other hand, since zoos can buffer the environment, especially for baby animals, and no one has looked for this specifically, I’m not taking any bets.

Within species … across clines or subspecies … this raises very significant (and addressable) questions regarding adaptation in the genetic vs. the ontogenetic realms. If Allen’s rule is primarily an ontogenetic effect in some species, one can still consider the possibility that it is adaptive, but the nature of adaptation becomes somewhat more nuanced. Which is appropriate, because adaptation is probably never as straight forward as the textbook version of it towards whic we tend to gravitate.

M. A. Serrat, D. King, C. O. Lovejoy (2008). Temperature regulates limb length in homeotherms by directly modulating cartilage growth Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0803319105

Personally, I think that most biological drives, maybe all, produce extreme or pathological behavior if unchecked, and that therefore all drives are repressed to some degree in almost all individual humans. There is considerable evidence that things like anger, thirst, or fear (to use highly generalizable terms) are manifest as a balance between limbic circuits that are excitatory or inhibitory; Experimental interference with one or the other circuit produces extreme results such as a rat that will not stop eating or a cat that will maintain an arch-backed bristle-haired stance until it falls over in exhaustion.

Also, I think that what I’m calling drives (again, as a convenience … you won’t find what I am thinking on Wikipedia) are a basic mammalian trait. Therefore, it is reasonable to ask if some of the evolutionary events related to the rise of new species of mammals are related to changes in drives, or more interestingly (and more commonly, I suspect) changes in how drives are on one hand repressed and on the other hand re-configured to work with each other.

Thus, one could say that since humans are behaviorally derived with respect to many traits in comparison to African apes in general, a major feature of the human brain must be mechanisms telling the rest of the brain, to some extent every minute of the day, “Don’t be a chimp …. Don’t be a chimp. Seriously, dood … don’t be a chimp.”

At the individual level, and I’m oversimplifying a great deal here, one might imagine drives being enhanced or repressed to a degree that makes an individual very different from others. The fictional character “Brennan” on the TV series Bones comes to mind. She seems most of the time to have no drives at all, or to be intellectually in denial of them. Social and psychological pathologies may often be associated with drives that are inappropriately strong or weak.

So, is it really true that behaviors are not “caused by genes” if there are these drives? Yes, and I say this because the average person who is thinking that behaviors are caused by genes is not thinking at all about intermediate mechanisms, and if they are, they are assuming that the intermediate mechanisms are little more than a transparent ether through which genes operate on the behavioral phenotypes we observe. Also, “genetic determinism” is not about whether or not one or more genes are involved in a trait, but rather (and this is very important so if you’ve got a yellow highlighter uncap it now) “genetic determinism” is about the close correspondence between variation across individuals in the genetic code they carry and the ensuing variation across individuals in the phenotype they express. Moreover, “genetic determinism” as usually conceived is presumed to average out within categories such as “race” or “sex” with very little variation within, but enough variation between these categories to be measurable. Which is why the concept is almost always racist or sexist or both.

But in reality, variation in the way limbic and other brain functions as well as closely related endocrine systems are manifest in humans and probably many other mammals is only to a small extent a function of genes, and is otherwise a function of what we may loosely call development. This relationship is not a post-hoc observation, or a liberal excuse, or a politically motivated bit of rhetoric. It is, rather, the explanation for why we have large brains that mostly develop, in detail, on the basis of experience rather than genetic coding for how they are hooked up. (And, while this applies mainly to mammals, something like it might be going on in some birds.)

Consider long term habituation. When endocrinologists (those who study hormones) measure hormone levels, they generally adjust the numbers to account for individual baselines, because while two individuals may have very different baselines they can have the same range of behaviors and responses. Two men may have androgen hormone levels that vary between them by a factor of 2X or 3X, but have the same basic behavioral repertoire. This is because of two things: First, the number of receptor sites and their sensitivity matters as much as, if not more than, the serum hormone levels; and second, most hormone systems are some sort of feedback loop that relies on changes in concentration against set points that are individually established, not species-specific. Putting it another way, if a hormone system is like a thermostat in your house (a homeostatic equilibrium system) then each individual has a personally established and potentially unique “room temperature.” This variation between individuals could be genetic, but is it just as likely, or even more likely, to be developmental. A related example is the mechanism by which we become “cold” or “warm” (with respect to comfort). This is not innate, but rather, a function of exposure to environmental conditions in early life (thigh there are body-shape related variations that probably are genetic that matter to thermoregulation in a non-industrial population).

Given huge piles of evidence for individual variation in behavior as a function of context, conditioning, and development and relatively little evidence that has not been made up, cooked up, or otherwise tainted or damaged for straight forward genetic determination of behavior, I’m going to go with the model that humans vary mostly on the basis of their biological and cultural experiences post-conception. For example, the single largest factor in variation in human intelligence in a given population can easily be prenatal alcohol exposure, or variation in folic acid in the maternal diet. Given the amount of post-conception stuff the brain does in development, and how much of that depends on experience, it is very unlikely that brain function varies across individuals on the basis of genes (other than individuals with genetic disorders, but we need not count broken individuals in considering normative development).

From what we know about “drives” and from what we know about brains and development, it is very reasonable to hypothesize that variation across individual human males in something like violence levels, likelihood to carry out rape, or other widespread and usually male-associated behavior is environmental. Yet, these behaviors at the base, the systemic potential for these behaviors, is a mammalian feature or a primate feature or a great-ape feature, depending on level of analysis.

This is not the place to discuss this in detail, but a quick digression regarding comparison among mammals is probably useful at this point in order to stem unnecessary direct comparisons that may come up in discussion. Maybe mammalian males in general have certain traits leading them towards violent or icky behavior, but the details are important. The fact that big horn sheep butt heads in contests sometimes to the death, taken as an extreme male-male competitive trait, can not be linked to similar behavior among human males (and such behavior does seem to happen in humans). The basal bovid-type organisms from which the big horn sheep derive was probably a small bodied monogamous forest dwelling animal in which males probably did not have a much greater tendency to butt heads than females, though both males and females would likely have employed some sort of “violence” in defending young or territories. Among primates, Old World Monkeys include a lot more examples of violent male behavior than do New World Monkeys. The latter group, in fact, have many cases of distinctly non-violent males as typical of the species. We don’t know the nature of the basal primate, but we cannot assume that it was like a baboon, which is the primate often taken as prototypical in thinking about primate social behavior. In fact, we can guess that it was probably NOT like a baboon for a number of reasons. Therefore, what might be thought of as “over the top” male behavior (butting heads to the death) is NOT a basal mammalian trait that may be found in humans because we are mammals. The phylogenetic link between big horn sheep and human football players is non-existent. (This is why many of us cringe with the latest “evolutionary psychology” finding!) Rather, violence in human males is either derived in our species or in a set of species closely related, including perhaps the great apes, or apes in general, or some other subset of Old World primates.

And, this would be a matter of evolution of drives in a very general sense which are then shaped in a maturing individual by other developmental tendencies and in social beings with large brains, buy culture.

Which brings us to the famous YanSan comparison.

There is an intellectual and pedagogic tradition that comes from people working out of a handful of American Universities (originally, Berkeley, Chicago and Harvard, but then other places such as Madison) having to do with the study of both primates and human foragers. The details are interesting but this is not the place for them. What is important is this: A lot of us (and I’m part of that tradition) learned some of our best metaphors, for doing both research and teaching, from Irv DeVore, who either came up with them himself or consolidated them from people with whom he overlapped or worked, such as Sherwood Washburn, George Gaylord Simpson, and others. And one of those tidbits, which is a comparison and a set of stories much larger than your average metaphor, is the YanSan comparison.

It runs like this. Imagine a Yanomamo village in the Amazon. The Yan (short for Yanomamo) live in a society that for various reasons incorporates a fair amount of violence among men. Men who have killed other men are given a special name of respect, tend to have more children than other men, and often have two wives (in a society in which while polygyny is allowed, it is rare). Then, in contrast, imagine a “San” (Busheman) community in southern Africa. The San live in a society of hunter-gatherers where variation in status among men, for any reason at all, is discouraged, and interpersonal violence is frowned upon. Among the Yan, disputes are settled with chest pounding duels or axe fights, while among the San, disputes are settled by endless discussion during which there might even be hugging.

That’s the background. The YanSan comparison itself goes like this:
In the day to day course of events, a Yan child may become upset or agitated as children occasionally do, perhaps in relation to another child. The good Yan father steps in. He brings his son to the center of the community courtyard and calls over the other child with whom the conflict has arisen, and that child’s’ father tags along. The two Yan dads equip the children with poles about the length of their bodies and set them up to whack at each other until one of them succumbs to injury. Or perhaps, instead of using the poles (because that can be dangerous … you can poke your eye out with one of those things) the dads teach the 6 year olds the rudimentary form of the chest pounding duel, in which each participant gets one free shot at the other’s chest, and you can use one fist or two to pound on your opponent. The participants go back and forth taking fee shots at each other’s chest until one falls to the ground. The one still standing wins.

Meanwhile, over in the San society which is entirely different, a perturbed child is treated differently. If a toddler or youngster is very upset, yelling, having a tantrum, any nearby adult who knows the child, often but not always a relative, will hold the child in both arms until he calms down (this can take considerable time), and then spend some time soothing the boy and telling him thoughtful thoughts.

In both cases, there is a set of drives typical for men, and there is a society in which there is expected, normative male behavior. But since the expected behavior is very different between the two societies the developmental process has a lot of work to do. Boys will not on their own grow up to be Yanomamo warriors with the proper kind of fierceness, and boys will not on their own grow up to be San hunters with a proper cooperative attitude, unless a great deal of cultural energy is expended.

And this is facilitated by the existence of childhood, which may well be Homo sapiens most important adaptation. The YanSan comparison exemplifies how humans transit from blastosphere to adult with respect to behavior, and demonstrates that there is a great deal of potential variation in what the result is, and thus, there is great potential variation in the sorts of societies that Homo sapiens can come up with.

But males are still demonic.

What I mean by that is this: Across all human societies, even when there is relative equality between males and females in power or other measures, males are the more violent sex on average. When human societies range into more violent normative behavior, it is males who are in the vanguard virtually all the time. There are plenty of cases where females are also violent, but they are comparatively rare and less extreme.

And, there are patterns to this behavior seen across society, and interestingly, there are even patterns of male behavior when males are viewed across species, as per the above discussion, among the great apes and in particular comparing chimps and humans. Those patterns may be accidental, they may be nothing more than basic mammalian behavior (or the behavior of an internally fertilizing lactating creature, on whatever planet it is found) and thus almost too basic to be meaningful, or they could be patterns around the specific nature of ape social systems, of which chimpanzees and humans have their own similar yet different versions.

Some years ago, Richard Wrangham, emerging as a leading primatologist, was woo’ed away from his home in Michigan by Harvard to do research and teach interesting courses. One of the courses he developed in his new milieu and taught to advanced undergrads in bioanthropology was about male behavior in apes, looking at the behavioral biology and culture of this behavior, seeking patterns, similarities, contrasts, etc. Over a short period of time this course became very popular. Knee-jerk feminists responded to the course with great disdain because it seemed to be biological determinism, but then some went ahead and took it anyway and found out that it was not. And eventually the course became a book: Demonic Males: Apes and the Origins of Human Violence

Many have criticized Wrangham’s book for suggesting that simple underlying genetic systems determine things like gang violence in humans, but few who have read the book have come away thinking that. It may well be that Wrangham’s view is somewhat deterministic, but that is hardly the point of the study. And, if you bring to the discussion, as Wrangham does, the concept of “drives” or similar psychological phenomena as I’ve described above, the genetic determinism that might be inherent in many comparisons between species’ behavior rather fades away. More interesting, though, may be the political nature of the problem of determinism, and this relates to the ongoing discussion of male privilege as well as to a previous discussion we’ve had on this blog about rape. Is it possible to attain the ideal feminist society (towards which we all strive) if male and female drives are somewhat different, and male drives are (or at least some of them are) so … dickish?

… a new philosophy has emerged in the last decades, an evolutionary brand of feminism that sees the emergence of patriarchy as an intimate part of human biology. Evolutionary feminists, writers like Patricia Gowaty, Sarah Hrdy, Meredith Small, and Barbara Smuts, agree with traditional feminists about the evils of patriarchy, but they do not disconnect humans from their biological past. The logic of evolutionary feminists appreciates the rich details of patriarchal history as recounted by historian Gerda Lerner, but it simultaneously rejects the notion of plumbing the human condition through reading merely the last 6,000 years of history.

Evolutionary feminists … would insist that people can think about the evolutionary pressures that elicit rape, for example or other forms of violence, without necessitating any absurd pronouncement that because rape is “natural” it is in any way forgivable. After all, no one considers the case of the black widow spider, who kills and eats her male counterpart after mating, to mean that murder and cannibalism are okay. …

Patriarchy is worldwide and history-wide, and its origins are detectable in the social lives of chimpanzees. It serves the reproductive purposes of the men who maintain the system. Patriarchy comes from biology in the sense that it emerges from men’s temperaments, out of their evolutionarily derived efforts to control women and at the same time have solidarity with fellow men in competition against outsiders.

(Wrangham 1996 pp 124-125)

It is interesting to consider the commentary emerging (mainly in comments but also in a few blog posts) around Rebeccapocalypse in light of this discussion. Most commenters are either on board with giving women the right to set their own level of concern about potentially dangerous men (those are the feminists) or they re busy making excuses or denying the demonic nature of male Homo sapiens. While many of the former are men (it might be about 50:50 men:women) the vast majority of the latter are men.

Just sayin’

In homage to an inspiration of this post, I provide this link to the secret, generally unseen obituary of Professor Irven Boyd DeVore.

Later in life, humans have a longer period of what might be called pre-adolescence than they “should” based on comparisons with related species. Some have characterized this as the insertion of a number of extra years of development. It could also be characterized as a period of time-lengthened development. Neither is perfectly accurate. One way to characterize the human condition for this period is this: From some time several months after birth through about the age of five or six (or more) humans engage in developmental activities not seen (or not as extensive or intensive) in other apes, during which humans learn a number of important things and engage in a number of neural developmental processes.

It is during this period that humans develop their knowledge of the kinship systems they will live with for the rest of their lives. Western populations tend to have poorly developed kinship systems, so this is easy to overlook, but virtually all other human cultures have complex and pragmatically significant kinship systems, and it is easy to observe children becoming aware of them and learning how to engage in them during this time. It is during this time that human children develop gender identity and gender roles appropriate to their society. They may learn class, caste, or ethnic roles as well. They start to learn the basics of the things they will need later in life, and what they learn is based entirely on what their society or culture requires: Being a blacksmith, a forager, a western/professional, whatever.

Most significantly, it is during this period that the child learns to use human language, a trait that is absent from our most closely related species.

Mel Konner, if I recall correctly, suggested the use of the term “childhood” as the period of development in which humans engage that is absent from the apes. (If he did not suggest that, he certainly popularized it with his documentary series called “childhood” and accompanying text.) The word “childhood” existed previously, of course. The term was suggested for use as the technical term referring to the inserted extra five years or so of development. Primates have a juvenile stage followed by the transition to sexual maturity, but humans have a pre-juvenile stage as well. This model can be rather clumsy, but suffice it to say that human young are doing something quantitatively and qualitatively different than ape young.

Primates tend to learn much of their ultimate adult behavior from the other primates with whom they live and by interaction with their natural environment, and this allows for certain things to happen, such as the development of behaviors that would be difficult or impossible to program genetically. This is a trait found widely in mammals and birds, but more so in some groups, including primates. It is even more true of the apes than of other primates, and indeed, apes have long periods of parent (mother) – offspring association, and are observed to engage in long bouts of learning and, remarkably, active teaching. Humans take this ape characteristic to a proverbial “order of magnitude” greater. One result of human hyper-extended and hyper-intensified child-age learning is the ability of human cultures to adapt (specialize) in a wider range of habitat exploitation strategies (lifeways) than otherwise possible. Indeed, the genetically coded behaviors that may well be present in primates (innate fear of certain things, certain aspects of territorial competition, sexual interaction, etc.) are often repressed or re-programmed in humans via culture. An interesting, though trivial, example is Heavy Metal. Heavy metal is a cultural manifestation (a “subculture”?) in which human participants revel in the instantiation of symbols almost all of which represent the repulsive, the dangerous, or the adaptively scary: Blood, predators, spiders, snakes, misplaced umlauts, and sharp things. That which we might reasonably guess would be genetically programmed into our beings is dragged out and made normal. This sort of thing proves that culture is capable of “overriding biology” (though that presumed relationship is often a falsehood) and suggests that human behavior in general may be primarily culturally coded rather than genetically coded. After all, culture is a powerful and rich source of information that can be passed on from generation to generation like genes, but altered in ways not possible with genes. One would expect selection to favor culturally mediated traits over genetically mediated traits.

And that may be our most important adaptation.

This is, of course, a parody of the sociobiological, or in modern parlance, the “evolutionary psychology” argument linking behaviors that evolved in our species during the long slog known as The Pleistocene with today’s behavior in the modern predator-free food-rich world. And, it is a very sound argument. If, by “sound” you mean “sounds good unless you listen really hard.”

I list this argument among the falsehoods, but really, this is a category of argument with numerous little sub-arguments, and one about which I could write as many blog posts as I have fingers and toes, which means, at least twenty. (Apparently there was some pentaldactylsim in my ancestry, and I must admit that I’ll never really know what they cut off when I was born, if anything.)

Before going into this discussion I think it is wise, if against my nature, to tell you what the outcome will be: There is not a good argument to be found in the realm of behavioral biology for why American Women shop while their husbands sit on the bench in the mall outside the women’s fashion store fantasizing about a larger TV on which to watch the game. At the same time, there is a good argument to be made that men and women should have different hard wired behavioral proclivities, if there are any hard wired behavioral proclivities in our species. And, I’m afraid, the validity from an individual’s perspective of the various arguments that men and women are genetically programmed to be different (in ways that make biological sense) is normally determined by the background and politics of the observer and not the science. I am trained in behavioral biology, I was taught by the leading sociobiologists, I’ve carried out research in this area, and I was even present, somewhat admiringly, at the very birth of Evolutionary Psychology, in Room 14A in the Peabody Museum at Harvard, in the 1980s. So, if anyone is going to be a supporter of evolutionary psychology, it’s me.

But I’m not. Let me ‘splain….

I want to first provide the argument from bottom up. Over the next few paragraphs I’ll outline why evolving during the Pleistocene made us what we are today, and what some evolved features of our species may be. Later, I’ll deconstruct the argument.

Organisms have genes that vary (the variants are called alleles). Sometimes a variant arises that, when interacting with the environment, confers a negative or positive effect. Those that confer a positive effect with respect to the process of passing on genes to future generations are over-represented (on average) in the next generation while those that confer a negative effect are under-represented. If the strength of this selection is sufficient and random effects do not overpower it, there may be a shift in allele frequencies over time.

That’s evolution.

Some behaviors vary because of underlying genes. The pattern of foraging by fruit fly larva, for example, varies in a way that has been mapped directly to specific base pair differences between alleles for a gene. There are a handful of other gene-behavior links (a handful relative to the total amount of behavior out there to study) but in most cases, the link between the underlying genetics and the resulting behavior is not directly documented, but assumed. This is reasonable. The link between phenotypic variation and the underlying genetic variation is almost always assumed and hardly ever documented directly.

Humans are mammals and thus have internal fertilization, internal gestation, and lactation. Each of these three important features of mammalian reproduction means a striking difference between males and females in the risks and benefits of behavioral practices, and in the very nature of reproductive strategies. Consider the very act of mating. A single copulation may have consequences that are extraordinarily different between a female and a male. A pregnancy followed by nursing and so on is a huge investment for a female, but virtually zero investment for a male. Copulating with the “wrong” mate (i.e., one that is somehow genetically not the best choice) has almost zero consequences for a male, who can simply copulate with some other female. A bad choice in mate for a female, however, may blow a huge percentage of her total reproductive career.

(Pause: In the above paragraph, I was writing about mammals. Voles, for instance. Or aardvarks. You may have been putting humans in there as your mammal of choice, but since the vast majority of mammals are rodents or bats, that may have been a bad idea. Please consider re-reading the paragraph and placing a wild, non-domestic ‘typical’ mammal in there as the fill-in organism, just in case your assumption that I was talking specifically about you was influencing your thinking on this.)

It is not at all unreasonable to expect that any mammal, including humans, would evolve such that there are male-female differences in things like risk-taking behavior, mate-preference, child-care proclivities, etc.

In particular, and this is very important, humans are the result of evolution over two million years or so of the Pleistocene, during which time our ancestors lived in a social setting that is represented today by the likes of the Ju/’hoansi Bushmen of southern Africa, who were intensively studied during the 1960s in part to learn about what the lifeways of our ancestors may have been like.

Furthermore, it has been proposed that the behavioral tendencies of humans are often fairly specifically hard wired protocols. We have the ability to do certain things because our brains are really a set of many different organs, including a set of cognitive structures called “modules” which were shaped by natural selection over these millions of Pleistocene years, a time that was pretty much similar from generation to generation, among people living in Ju/’hoansi Bushman like groups in the tropics and subtropics of Africa.

These modules provide the ability to be very good at certain things. When these modules are tested or challenged in modern-day humans living in the West, we see that we are still good at doing some of the things that we did back in the Pleistocene but no longer need to do today, and we often show poor performance when it comes to modern, western, industrialized, non hunter-gatherer or non-Pleistocene problems or contexts. Just as our hand eye coordination evolved to facilitate the use of tools, our brainy bits evolved to detect certain kinds of cheaters but not others, have a taste for rare but not common nutrients, and so on. Most importantly relative to the current discussion, males have a module that facilitates promiscuous sexual behavior and females have a module (probably the female version of the same module, according to the theory) that makes them relatively prudish and careful about sexual relationships. Males have abilities to orient things in time and space in order to better shoot the antelope with the spear, while women have the ability to remember details of things in space in order to better find and select the proper plant foods. And so on. Thus, males show off, fight other males, and practice hunting by playing hockey, baseball, and football, or at least, watching the games and knowing every detail of the statistics, while females … shop and stuff.

It’s a nice theory and there have been a lot of studies supporting the basic idea as well as a number of specifics. However, there are some problems.

Let’s start with the Pleistocene. The Pleistocene is, among recent geological time periods, considered to be the most variable in terms of climate change, and thus, overall ecology, habitat distributions, etc. There is no expectation that any given population making up part of a species like humans or their close relatives would have had any long term consistency in natural environment. Indeed, the post-Pleistocene life of the horticulturalist, buffering their food supply by growing crops, is probably more consistent over time than any period in the Pleistocene, with respect to basic ecology. Furthermore, when we look at foragers across Africa today, and at the archaeology which tells us something about their past, we see a huge amount of variation in habitats and adaptations to habitats. Humans have lived in very arid environments and very wet environments, coastal and inland, riverine and woodland, grassland and forest. Post-Pleistocene food producing human groups tended to avoid several of these habitats and have lived in a much narrower range of contexts.

One might argue (and this is the usual argument) that it is really the social setting in which humans lived, not the habitat, that was consistent over two million years, thus the Pleistocene as a variable time period argument goes out the window. But I should point something out about that counterargument: It wasn’t ever made until people like me (mainly me, in fact) started arguing, mainly at conferences, that the Pleistocene varied too much to be thought of as a stable habitat in which certain behaviors would evolve and get “stuck.” You see, part of the Pleistocene argument is that it was a long time compared to the subsequent Holocene (two million vs. 10,000 year) so we are essentially Pleistocene creatures. But when it was pointed out to evolutionary psychologists that the Pleistocene varied tremendously compared to the Holocene, the “oh, it’s the social argument” was raised to salvage the idea.

But that doesn’t work. We know that habitat determines social structure in humans, with technology as a major factor. Foragers vary a tremendous amount in their behaviors, depending in large part on the ecology in which they live. Forager group size, often considered to be an important intermediate variable between ecology and social structure, varies tremendously with habitat. There are even foragers with stratified societies and slavery, and there are foragers who live in such small isolated groups that they need special cultural conventions to get together now and then in order to socialize, find mates, and so on.

There is also variation in important social norms beyond that which can be explained easily by ecology. For instance, it is probably fairly rare for an Efe Pygmy woman’s offspring to have been fathered by anyone other than that woman’s husband at the time of birth (though with serial monogamy a woman may have different children fathered by different men). In contrast, the Ache and other foragers of the Amazon seem to pay little attention to who is the father of whom, and it is common for a woman to have children fathered by several different men other than her long-term husband. These are very, fundamentally, even dramatically different social systems, found in tropical rain forest foragers. Efe Pygmy men compared to Baka Pygme men spend dramatically different amounts of time caring for their own children. Add to these examples the diversity that must arise in groups living across a range of different habitats, and we pretty much have destroyed the argument of one social environment in which we evolved for two million years. If the basis of the modern evolutionary psychology argument is falsified, the rest of the argument may be … well, weak at best.

When this argument … that the social Pleistocene was a weak idea … was proposed, the counter argument was this: Sure, the social environment changed, but there are still some basic things that are always the same: Predators and the need to mate being key.

Fine. So now, the Environment of Evolutionary Adaptiveness (EEA), which this thing … this time period … is called is “Predators and mating.” How do we distinguish, then, between evolution in humans vs. evolution in mammals, or even tetrapods, or for that matter, organisms, in general?

We don’t.

Then, consider the foragers used as exemplars in the studies done today in evolutionary psychology. A disturbing trend has emerged over the last five or ten years: The use of groups that are not foragers as though they were foragers. For some reason, it is very common today to see evolutionary psychologists claim that the homicide rate and level of violence among Pleistocene foragers was very high. There is, however no evidence whatsoever to support this. When we look at the evidence that is being adduced, we find that several groups of food growers, horticulturalists such as the Yanomamo of the Amazon, have somehow been included in the sample of “foragers.” I can’t decide if this is ignorance (the researchers have no clue what they are doing), intellectual dishonesty (the researchers need violent ancestor so they cook the data) or merely a tradition of indifference (the researchers use some data they got somewhere that someone else used, so they use it uncritically).

The Yanomamo and other groups like them do indeed have high rates of violence and homicide. It has been effectively argued that this violence arises because thy have horticulture. The thing that makes them different from foragers in terms of habitat and ecology also makes them different from other groups in terms of behavior.

Then there is the argument about the modules. Let’s assume that the research that shows how modules seem to work and what they seem to “look like” functionally is good. The fact that humans are running around with modules today does not mean that these modules are genetically programmed. It is very possible that module-like structures in our neocortex arise during development, de novo, in each of us, and that these modules are similar across groups (but perhaps different sometimes by gender) because of overall similar developmental trajectories. The cases of modules failing, say, to detect cheating if the cheating is modern (non-Pleistocene, if you will) in context is unimpressive. In one famous study, people were shown to be very good at detecting cheaters when the cheater was someone possibly lying about their age to get a drink in a bar, but very poor at detecting cheaters when the cheater was a file folder in an esoteric filing system that may or may not have been filed correctly. In other words, when comparing actual social cheating to a glitch in a filing system, humans were pretty good at the social cheating part but not so good at the arbitrary artificial strange filings system. We are not impressed.

There are dozens of reported gender differences, with piles of research demonstrating them. But when we look more closely, we often see that the either a) the methodology of the research sucks or b) the gender difference, while likely real, changes, goes away, or even reverses as times change, suggesting that the difference is (was) cultural.

I’m sure there are gender differences. Part of the reason I think that is an inappropriate argument: I think there are gender differences in behavior because there must be. Such an argument is not evidential and does not lead us to a legitimate conclusion. Rather, it leads us to a set of valid hypotheses, if done right. However, I am utterly unconvinced that most gender differences are hard wired. There are probably some. Testosterone poising of neural tissue (indirectly) during development probably accounts for the fact that there are almost no male simultaneous translators. The neural ability to do this difficult thing is retains in some females but lost in almost all males during puberty. That is not genes coding for neural connections, but it is genes coding for different endocrine systems which then, through a series of negative and positive feedback systems, cause hormonally mediated changes in the body (including the brain).

Perhaps hormones make men like sports and women like shoes. But if so, it is not very consistent. My wife has three pairs of shoes and one purse. I have two pairs of shoes and four laptop bags. My brother-in-law knows more about sports than anyone in my wife’s sports-oriented family. But his new wife knows twice as much as he does, even though no one in Andrew’s family has quite admitted this out loud yet. I can track my own interest in both baseball and football as a function of a female mate or friend who had such an interest, with my involvement being a way to socialize and get along. I find sports interesting enough to pay attention and to enjoy it, but if I want to know what is going on, I have to ask the female I’m watching the sport with (often, but not always, my wife). Yes, I guess I’m following my true genetic nature: I’m somewhat promiscuous as to whom I watch the game with.

Sex differences are probably real and probably important, but they may not be hard wired as often as people think they are, or hard wired in the manner people think. We would expect a species like humans, born with this big blank brain and subjected to many extra years of learning as children, to develop these differences as a function of culture rather than genes. That, to me, is the most likely null model. I’m not sure I would attribute a priori much likelihood to a genes-up model of human behavior. How the heck would that work, anyway?

If you enjoyed this, or even, if it made you mad, you might want to check out these two posts:

• The natural basis for gender inequality
• Women are smarter than men (well, duh!)

This post is part of the Falsehoods II series, which are also explored on “Everything you know is sort of wrong” on Skeptically Speaking, with Desiree Schell.

And, please do feel free to tweet, digg, redit, stumble, etc. this post by using the buttons below!!!!

A comparison of the orbits of the pulsar J1903+0327 and its possible sun-like companion star with the orbit of the Earth around the sun. The objects’ sizes are not to scale. (Bill Saxton, NRAO/AUI/NSF)

(More at Cornell)

Observing Stem Cells at WorkFrom a Fraunhofer-Gesellschaft Press Release:Stem cells can differentiate into 220 different types of body cell. The development of these cells can now be systematically observed and investigated with the aid of two new machines that imitate the conditions in the human body with unprecedented accuracy.Stem cells are extremely versatile: They can develop in 220 different ways, transforming themselves into a correspondingly diverse range of specialized body cells. Biologists and medical scientists plan to make use of this differentiation ability to selectively harvest cardiac, skin or nerve cells for the treatment of different diseases. However, the stem cell culture techniques practiced today are not very efficient. What proportion of a mass of stem cells is transformed into which body cells? And in what conditions? “We need devices that keep doing the same thing and thus deliver statistically reliable data,” says Professor Günter Fuhr, director of the Fraunhofer Institute for Biomedical Engineering IBMT in St. Ingbert.Two prototypes of laboratory devices for stem cell differentiation enable the complex careers of stem cells to be systematically examined for the first time ever. These devices are the result of the international project ‘CellPROM’ – ‘Cell Programming by Nanoscaled Devices’ – which was funded by the European Union to the tune of 16.7 million euros and coordinated by the IBMT. “The type of cell culture used until now is too far removed from the natural situation,” says CellPROM project coordinator Daniel Schmitt – for in the body, the stem cells come into contact with solute nutrients, messenger RNAs and a large number of different cells. Millions of proteins rest in or on the cell membranes and excite the stem cells to transform themselves into specialized cells. “We want to provide the stem cells in the laboratory with a surface that is as similar as possible to the cell membranes,” explains Daniel Schmitt. “To this end, the consortium developed a variety of methods by which different biomolecules can be efficiently applied to cell-compatible surfaces.”In the two machines – MagnaLab and NazcaLab – the stem cells are brought into contact with the signal factors in a pre-defined manner. In MagnaLab, several hundred cells grow on culture substrates that are coated with biomolecules. In NazcaLab, large numbers of individual cells, washed around by a nutrient solution, float along parallel channels where they encounter micro-particles that are charged with signal factors. “We use a microscope and a camera to document in fast motion how individual cells divide and differentiate,” says Schmitt. The researchers demonstrated on about 20 different cell models that the multi-talents can be stimulated by surface signals to transform themselves into specialized cells.Large scale carbon sequestrationFrom Indiana University:Indiana Geological Survey scientists at Indiana University will participate in a new $67 million U.S. Department of Energy project to test the feasibility of storing carbon dioxide at underground sites in Ohio and Indiana.The evaluations are being carried out with the Midwest Regional Carbon Sequestration Partnership, a research consortium of government, academy and industry researchers led by Columbus, Ohio-based Battelle Memorial Laboratories.One million metric tons of carbon dioxide, a greenhouse gas, will be diverted from a Greenville, Ohio, ethanol production facility for use in the study. The gas will be pressurized at the site and injected 3,000 feet underground into a saltwater-filled geological formation called the Mount Simon Sandstone. Scientists will evaluate the ability of the rock to securely contain the injected carbon dioxide. The sandstone is capped by a extensive layer of dense shale that prevents the relatively light carbon dioxide from escaping upward. Scientists also plan to evaluate the area surrounding a Duke Energy Corporation gasification power plant now being constructed at Edwardsport, Ind.In the middle of this diagram created by U.S. Geological Survey staff, carbon dioxide is routed from its emissions source (a power plant) to various storage “reservoirs” underground. The current DOE project will look at the storage of carbon dioxide in a 3,000-foot-deep saline aquifer. (Indiana University)“As experts on the regional geology, the Indiana Geological Survey will support Battelle’s overall evaluation of the sequestration technology by providing detailed information about the character of the reservoir rock as well as the seal,” said John A. Rupp, assistant director of research for the survey, an Indiana University research institute.The evaluation, injection and monitoring of carbon sequestration at the Ohio site will take approximately 10 years. This latest project is actually Phase III of the U.S. Department of Energy’s efforts to determine whether carbon sequestration is an effective approach toward reducing anthropogenic (human-caused) carbon dioxide emissions. Phases I and II determined the location of possible carbon dioxide reservoirs and examined how some of those reservoirs handled small-scale injections of carbon dioxide, up to 10,000 metric tons. Six Phase III tests have been funded at various localities around the nation; each will evaluate large-scale — one million tons — storage of injected carbon dioxide.Rupp says carbon sequestration is only part of the solution to humanity’s greenhouse gas problem.”Large fossil fuel-burning facilities can generate tens of millions of tons of carbon dioxide per year,” he said. “If we want to reduce anthropogenic emissions using carbon sequestration, we will have to deploy this technology on a massive scale. Ultimately we’ll need to include other ways of reducing emissions.”

A major proportion of the mammalian transcriptome comprises long RNAs that have little or no protein-coding capacity (ncRNAs). Only a handful of such transcripts have been examined in detail, and it is unknown whether this class of transcript is generally functional or merely artifact. … we identified 849 ncRNAs (of 1,328 examined) that are expressed in the adult mouse brain and found that the majority were associated with specific neuroanatomical regions, cell types, or sub cellular compartments. … Comparisons between the expression profiles of ncRNAs and their associated protein-coding genes revealed complex relationships that, in combination with the specific expression profiles exhibited at both regional and subcellular levels, are inconsistent with the notion that they are transcriptional noise or artifacts of chromatin remodeling. Our results show that the majority of ncRNAs are expressed in the brain and provide strong evidence that the majority of processed transcripts with no protein-coding capacity function intrinsically as RNAs.

The research was done by looking at data from an “atlas” – the ABA – of the mouse brain, which is a huge pile of information on DNA known to be expressed in each part of the mouse brain. (There are atlasses for other species, including humans, and the present study also lookd in the human atlas.)An example of patterning in ncRNA is with antisense transcribed genes (that is a common way that genes are expressed in mammals):

Transcriptional profiling has shown that antisense transcription is prevalent in the mammalian genome (33), and several studies indicate its importance in regulating diverse biological functions. We identified 44 ncRNAs in the ABA that are antisense to the exons of protein-coding genes… These antisense ncRNAs often share varied and complex expression relationships with their sense protein-coding transcripts. For example, P-rex1, a gene involved in neuronal migration, and its antisense ncRNA partner are both expressed in the cerebral cortex (Fig. 2b). However, in the cerebellum, P-rex1 is specifically expressed in the Purkinje cell layer, whereas the associated antisense ncRNA is expressed within the granular and molecular layer (Fig. 2c).

That’s a little thick, but we can parse it. This observation as well as other observations made in this study are relevant because of the following hypothesis: ncRNA is an artifact, or a side effect, of gene expression. This predicts a random but correlated pattern of association … where a gene is expressed, the associated ncRNA bits should be found, more or less, like the sawdust from your bookshelves is found on the floor of your garage only when you make bookshelves in your garage. If the ncRNA is missing sometimes where related transcription happens, or if it is more abundant than it should be, depending on what tissue you look in (your garage vs. your bathroom… different tissues in this analogy), then this hypothesis is untenable. This would suggest that ncRNA is not functionless.ADDED: I recommend this critique of the study at Genomicron.

Mercer, Tim R., Marcel E. Dinger, Susan M. Sunkin, Mark F. Mehler, and John S. Mattick. (2008) Specific expression of long noncoding RNAs in the mouse brain. PNAS | January 15, 2008 | vol. 105 | no. 2 | 716-721, Open Access Article