Or, when the hunting season is closed, watch teh game (the guys), or when there are no sales, admire each other's shoes (the gals)?

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:

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.

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