This ‘apples and oranges' approach finds support in two main sources. First, this approach is sustained by our basic intuition and affirms the order of the world we see around us. All of us see daily examples of marked differences between male and female behavior, appearance, and attitude. When my daughter's female teenage friends would come to hang, they would immediately pile on the bed in her room, giggle and watch a movie about a girl who's in love with a boy who ignores her because he does not know what's good for him (and he's also a vampire). When her male pals would come to hang, the house would fill with running, jumping and yelling, and in short order some vase would break in the living room and some lumbering schmo would tumble into the pool in his clothes. These kinds of differences between the genders we see all the time around us, and we tend to believe that what we see around us is the natural order of things.

Second, men and women have different physiologies, which emerge from their innate genetic differences. These physiological differences between the genders are real and nontrivial. Masters and Johnson, for example, pioneers of the scientific study of human sexual physiology, documented up close and with precision more than 10000 intercourse cycles. Their data show clearly that in the realm of orgasmic athletics, women trump men hands down (no pun). The man, they found, is an old rifle in the hands of a drunk. He has but one bullet in the chamber, hurries to discharge it, often accidently and without much aim, and then takes 30 minutes to reload, if he's not out of ammunition altogether and if he hasn't fallen asleep in the process. The woman, on the other hand, is a sophisticated semi-automatic weapon; she can fire in rapid succession, and doesn't run out of ammo (although her intricate mechanisms sometimes jam, and sometimes she doesn't feel like going to the shooting range, she feels like going to Starbucks).

Physiological differences inevitably lead to differences in how we move in the world. If I have nimble feet and you have big wings, and we both encounter a hungry lion on our afternoon walk, chances are I'll escape by running while you escape by flying. The differences in behavior and functioning between the sexes, therefore, are rooted in the fundamental physiological differences between them, and you cannot help that. There is, after all, no known society in history where gender differences did not exist.

These are strong arguments, but they're not bullet proof. First, what we see around us is not necessarily a natural order. This mistake is known as the naturalistic fallacy. In biblical times, slavery was seen as a state of nature. The bible says not a thing against slavery. Today, even avid bible thumper won't dare speak in favor of slavery. Second, not everything that is intuitively and easily comprehensible is also true and factual. The fact that we are stuck on a rotating ball in the middle of endless space is neither intuitive (when I look out my window the world doesn't appear round or rotating) nor easy to grasp. (Infinite space? With no beginning or end? Are you high?). Still, it is fact.

Third, the argument that genetic differences inherently give rise to differences in behavior and functioning is problematic. Genes do not establish traits or behaviors, they establish potentials. The path from genetic potential to actual behavior in the world, from genotype to phenotype, passes necessarily through the social environment. Society, in this context, influences genes in two primary ways. First, it decides how much of your genetic potential will be fulfilled. Your genes may predispose you to be six foot four, but if you grow up malnourished, in a neglectful early environment (social conditions) you will not achieve your potential height. Second, society controls the manner in which you will express your genetic potential. A big, strong, agile man may find himself on a football team, if he's American. If he's Japanese he may find himself on the sumo mat. Our DNA doesn't have a ‘football gene' or a ‘sumo gene.' Those are paths created by society.

These kinds of realizations and data about the crucial role of the social environment in shaping behavior and identity--along with the political, cultural and ideological changes since the 60s in the West--have given rise to a second approach, which holds that manifestations of difference between the genders are not natural or innate but rather artifacts-byproducts of the social order.

Femininity and masculinity, in this view, are not innate qualities but learned constructs and acquired habits. Children learn to be feminine or masculine like they learn everything else: by modeling, imitating, and following the rewards. Baby Jon receives praise for being big and strong (What a tiger! There, go catch that ball!). Baby Joan receives accolades for her daintiness (What a sweetie! Here, let me hold you so that your cute skirt doesn't get rumpled). These kids follow the path of rewards and shape their behavior accordingly.

The prediction emerging from this view is that a change in the social norms would bring about a change in gender behavior, identity and consciousness. Give baby Jon dolls to dress up and baby Joan trucks to smash, and within a few generations you'd see women yap blithely about torque, wipe their greasy palms and pine for quickie sex in the gas station bathroom; you'll have men struggling to decide which shirt fits their mood today and dreaming of an endless honeymoon in Greece.

This approach has scored some significant wins in recent decades. The range of behaviors and attitudes included in our definition of masculine and feminine has opened, expanded, and become more balanced. Women today can wear pants, run a business, and have one night stands. Men are allowed to be stay-at-home dads, pluck their eyebrows, and cry in a romantic vampire movie. And yet, even in the most open and progressive of homes you'd be hard pressed to find that baby Jon elects to dress up Barbie or that baby Joan smashes trucks for fun (although she may be happy to smash Jon). Even in the most progressive cultures, men rate body shape over social status in their mate preference priority list, and women rate status over a pretty body for their preferred male mates. For men, across cultures, sexual attraction is still mostly a ‘this or that' proposition--more attraction to one gender predicts less attraction to the other. Not so for women, who often manifest a ‘this and that' pattern. And the capital of nose jobs is not Hollywood, but Tehran. You can open or close the social structure, yet the whisperings of evolution remain strong.

And so we return to the question: which approach is right? What is the primary determinant of our gendered selves, innate genetic forces or learned cultural habits?

At the end of the day, both approaches are wrong, mostly because they are both right. Genes and environment don't operate in exclusivity, but rather in tandem. Men and women are not alien species to each other, but neither are they clones. There are predictable innate differences between the genders. Society can choose to work to minimize or maximize these differences; it can change the meaning attributed to them; but, at least up to now, it has not found a way to erase them.