We love simplicity. If during your gestational period you wind up with an X and a Y chromosome, you enter the planet male; two exes, female. Nature elegantly presents its basic arguments; like a yin-yang, balance is king.

But that Taoist symbol reminds us there’s a little black in the white. Much of existence resides beyond polarizing opposition—the grey is where many play. Our bodies are no different. English endocrinologist Gerald Swyer discovered this in 1955.

Certain women, he found, are born anatomically and physiologically female, though when puberty comes knocking, they do not reach full sexual maturity: breast development is stunted; the pelvis and hips remain narrow; menstrual periods are absent. As it turns out, every cell in their body is chromosomally male. If hormone replacement therapy is not offered, they might never reach womanhood.

Where does such a woman fall in the spectrum of sexuality? By society’s standards, female, at least through their teenage years. (Some develop ‘streak gonads.’ If not surgically removed they risk tumor development.) Perhaps more interestingly at this moment, how do they identify sexually?

In The Gene: An Intimate History, physician and author Siddhartha Mukherjee contemplates the difference between sex identity and sexual identity:

Whether sex is innate or acquired in the one-in-two-thousand babies born with ambiguous genitals does not typically incite debates about inheritance, preference, perversity, and choice. Whether sexual identity—the choice and preference of a sexual partner—is innate or acquired does, absolutely.

With a ludicrous debate over transgender bathroom rights occurring at state and local levels following Obama’s bathroom directive—eleven states are now suing his administration—gender identity has become the media’s cause célèbre. According to Mukherjee, the nature/nurture debate, which has raged in the public discourse over the last century, is unwarranted.

It is now clear that genes are vastly more influential than virtually any other force in shaping sex identity and gender identity—although in limited circumstances a few attributes of gender can be learned through cultural, social, and hormonal reprogramming.

It is understandable why gender identity infuriates the religious mind, as it calls into question the design of our vessel. Throughout his book, Mukherjee examines step-by-step our ever-deepening comprehension of the building blocks of life. Many follies have occurred along the way—the debate over gender identity is only the latest.

Rewind 2,400 years and we discover Greek philosopher Anaxagoras claiming that semen production in the left testicle results in male babies, while the right produces a girl. While such a theory is absurd, Mukherjee notes that it did place a seed into public consciousness: sex identity is random and not chosen, an important cognitive step forward from the chains of determinism. Jump ahead six hundred years to find the influential Greek physician Galen claiming that ovaries were merely internalized testicles.

Oddly, in all those millennia some still have not come to terms with the randomness of evolution. Initiatives like ‘praying the gay away,’ illegal in many states, still inspires forlorn parents to send their children to deprogramming camp. This is where the continual danger of genetics lives in the public imagination.

With many chapters devoted to the maturation and legacy of eugenics, most famously the Nazis (which actually did the world an unintended favor by making us aware of the lunacy of selective breeding), Mukherjee foresees dangers of tinkering with our microscopic software. While we do not yet understand the exact nature of the heritable elements that influence our sexual identity, that day is not far off.

What we do know now, as he explains to NPR, is that sexual identity is not an aberrant condition, but part of our genetic history. Environment can play some role, though Swyer Syndrome reminds us that a master regulator gene has the potential of influencing your identity.

Mukherjee compares the master regulator to an army commander. At top of the hierarchy is gender anatomy; countless variations exist downstream in the composition of the army, each with slightly different components. You might have male identity with differing sexual attractions, or you might have differing aspects of male identity. He continues,

The way that these genes—this genetic information percolates down into the individual, the way this hierarchy percolates down into an individual might be very different from one person to another and therefore create the kind of infinite ripples or variations in human identity that we experience in human life.

Early in his book Mukherjee warns of treating genetic mutations as mistakes. Mutations are responses to environments, internal and external. Thousands of years of believing in the formation of an ‘ideal’ race—the Spartans were especially keen on selective breeding—have resulted in chronic cultural wars and countless suicides, imprisonment, and social grief.

From single cells to the seemingly boundless array of life on this planet today, nature is our profound creator. Believing philosophical or moral programming lays behind the switches results in much suffering, as another Siddhartha warned. As Mukherjee told the New Yorker Radio Hour,

What we used to call fate, or destiny, is really a combination of random chance and environmental triggers impinging on the genome. 

This relationship is our actual inheritance. Celebrating it in all its varied forms will be immeasurably more beneficial on future genomes than constantly tinkering and thwarting the splendid diversity of our kind. 

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Image: Yasuyoshi Chiba / Getty Images

Derek Beres is a Los-Angeles based author, music producer, and yoga/fitness instructor at Equinox Fitness. Stay in touch @derekberes.