"Well I'm not the world's most masculine man / but I know what I am, and I'm glad I'm a man / So is Lola." In 1970, Ray Davies suffused rock culture with its first transgender icon. Two years later, Lou Reed solidified gender bending in the lexicon of every teen who strolled suburban streets singing, "Hey babe/ take a walk on the wild side."

Transgender issues have gone beyond pop culture as underscored by a recent U.S. Dept. of Health and Human Services decision in favor of a transgender veteran. The HHS ruled the government could not exclude gender reassignment surgeries from treatments covered by the national health program for the elderly and disabled.

The response highlights just how misunderstood transgender people are by the general population, drawing comments equating reassignment surgery to getting a tummy tuck, a voluntary procedure that makes you "feel better about yourself." In fact, meta-analyses indicate a lifetime prevalence of attempted suicide in transgender individuals at 41 percent as opposed to 4.6 percent in the overall population. People who don't get their Botox injections may not like their wrinkles, but they don't try to kill themselves. Being transgender is not simply a matter of wanting to look better, it is a fundamental discord between innate identity and how individuals are categorized and treated by society.

Therein lies the first hurdle -- understanding the intricate and complex interaction between biology and culture. Both academic disciplines and the popular press set up a false dichotomy treating these two important forces as separate and isolated. In the recent Time magazine cover story on transgenders, the author states, "Sex is biological, determined by a baby's birth anatomy; gender is cultural, a set of behaviors learned through human interaction."

Two major problems with this conclusion is, first, the assumption that sex is solely defined by penises and vaginas, ignoring the fact that one of the most important sexual organs is the brain: It is this biological collection of gray and white matter that actually determines gender identity. Studies of xy males and xy male to female transgender subjects have shown significant differences in the size of specific brain regions, as well as in the numbers of neurons and the chemical signaling systems within those regions. How these differences arise and precisely how they relate to gender identity is not known, but there are differences in the brain that correlate with gender identity. And the brain is biology.

The second problem is the implication that gender identity is solely a cultural phenomenon. There is no argument that the definition of gender is sociologically and culturally defined. But to suggest gender is only a manifestation of culture is to suggest gender identity is solely a matter of choice, like whether we put our salad forks on the outside of dinner forks at a place setting. Gender definitions may broaden as society changes (e.g., Facebook's new option to customize gender identity). But it is unlikely that societies across the globe will soon come to recognize greater than 50 different gender identities, and efforts to combat the discrimination and dysphoria reflected in suicide statistics of transgender individuals are more likely to succeed if our understanding of biology is not divorced from the efforts to change cultural norms.

And of course, the above discussion doesn't touch on the misunderstanding and derision that swirls around the fact that the HHS decision is pertinent to the elderly and Medicare. Stephen Colbert's riff on this implied old people don't have active sex lives (a subject for another day), so just put old guys in a muumuu and save some bucks. The routine was great, and Colbert may get the difference, but the subliminal message doesn't help dispel the misconception that gender identity is only important in terms of sexual activity.

There is a wealth of information on how early hormonal, genetic and epigenetic events impose permanent differences in brain structure and function that contribute to conventional male vs. female-specific behaviors in animals. There are studies demonstrating that interfering with a specific brain region in male ferrets can switch partner preference from female to male. Is gender identity shaped by similar forces? We have no idea what kind of gender identity non-humans may have (and biologists should stop referring to mice and rats as having gender). Moreover, we do not know if these biological processes are in turn influenced by environment and culture in ways that could shape gender identity.

However, as society grapples to change how our culture defines gender, it would be wise to do so by integrating, not ignoring, the significant role our brains and biology play in this fundamental trait.