by Paul Aitken Back in the 70s, when I was on the verge of adolescence, I remember watching an episode of Hawaii Five-0 in which a man who had confessed to a series of rapes was revealed to be impotent. When Jack Lord's hard-boiled Detective Steve McGarrett asked the man why he would take the fall for such a heinous crime, the man admitted that he didn't want people to know that he "wasn't a man anymore." McGarrett shook his head in dismay and said. "You have no idea what it is to be a man... You haven't a clue!" We never did learn what constituted the essential masculine to Steve (presumably getting ones dick hard enough to penetrate a woman's vagina wasn't it), but the question tugged at my prepubescent existential doubt and still does to this day. What is it that makes us men? According to my dad, a man was any male who was over the age of 21. In certain tribal societies it's any male who's undergone the tribal initiation ritual or been tested in combat. I personally felt that I was a man when I grew taller than my mom at age 14, but later, was led to understand that my status as a real man was in limbo unless I could down ten beers in one sitting. Given the subjectivity inherent in the definition, perhaps we should rephrase the question. What is it that makes us male? The answer to this is both simpler and more complex than we might assume at first glance. It turns out that it's damnably hard to isolate the sin qua non of masculinity. Sure, generally speaking, if it stands to pee, then it's a guy, but talented women have been known to piss upright like John Wayne, so that's not definitive. Having a dick and balls is another strong indicator, but even that's not absolute. We've all seen pictures of chicks-with-dicks and it's estimated that one out of every 3,000 - 4,000 children sport both ovaries AND testes. Now, I know you brainiacs out there are musing impatiently; "Oh please. It's sooo obvious. It's in the genes, man. If it's got a Y chromosome it's a he." Some of you who've taken a couple of biology courses and are feeling your oats might sniff aloofly that it all comes down to a component of the Y chromosome called the SRY (sex determining region of the Y chromosome) gene. If the SRY gene is present you get a guy, if not, you get a girl. End of story, right? Well, not quite. In the vast majority of cases the if-you've-got-a-Y-you're-a-guy rule holds. Even children with one or more extra X chromosomes (XXY and XXXY) are to all intents and purposes male. In rare cases, during meiotic recombination between the X and Y gene, the SRY gene can be translocated onto the X chromosome. When this happens the child will genetically be a girl (XX), but thanks to the presence of the SRY gene on the second X, will develop into a male complete with one dick, two balls and a multitude of Jessica Alba posters on the walls. He may never even know his genetic status until he and his wife try to figure out why she can't get pregnant. XX males are always sterile. No one knows precisely how the SRY functions but it appears to be a switch that turns on sometime during the fourth week of gestation, shunting the fetus away from a default female destination to a male version. Specifically, the proteins that the SRY produces bind to other sections of DNA, distorting their shape. This alters the expression of other genes which are themselves associated with other genes that are associated with other genes that are... associated with testes formation. Got it? As I mentioned before, nobody knows, but it's clear that sexuality is a manifestation built on processes that are themselves built on other processes. How many layers are in this scaffolding we can, at this point, only guess at. The complexity of the process is hinted at by two well documented exceptions to the rule: XY females and XX (sans SRY) males. XY females are genetically male but are in every outward respect female. With XY females, fetal testes begin to grow during gestation and start to secrete testosterone. But thanks to a genetic mutation, or combination of mutations (some of which are thought to be located on the X chromosome - androgen insensitivity can be passed down by way of the mother), the surface receptors on critical cells don't recognize this testosterone or it's metabolite, dihydratestosterone (DHT). The fetus accordingly fails to undergo the secondary stages of male fetal sexual development (which seem to be driven almost entirely by hormones). Depending on the type of mutation involved, androgen insensitivity can result in the whole spectrum of gender mash-ups, from males to hermaphrodites to smokin' hot babes. It was rumored for a while that Jamie Le Curtis was an XY female. While this rumor seems to have been scotched, the basis for it is grounded in real science. With XX (sans SRY gene) males, the picture gets even murkier. Somehow, in the absence of the sex-shifting gene, testes are formed, testosterone is produced; and when the baby pops out, his room gets painted blue. How this can happen is anybody's guess. Some scientists have speculated that perhaps the default sex is NOT female after all. In this scenario, the SRY gene acts to "repress an inhibitor of male testicular development." In case you didn't notice, that is the molecular equivalent of a double negative. Instead of being a guy because you're not a female, you're a guy because you're not not a male. Whatever is happening, it's clear that these XX (sans SRY) males have a mutation that affects a process that runs deeper than what the SRY gene affects. If your head is reeling with all of this, try thinking in terms of a computer metaphor. Sexual determination (and all development) is a sub-routine built on top of other sub-routines. At the very base of all this lies a machine language that is almost indecipherable. What has happened with these various mutations is that they've uncovered a backdoor code, a genetic atavism from a much earlier period when sexuality was determined by extra genetic or autosomal (any chromosome other than the X and Y) factors. In reptiles, sexuality is determined by temperature at a critical stage in embryo development. Warm egg - boy reptile; cool egg - girl reptile. In birds, sexuality is determined by an entirely different set of genes on different chromosomes. And in the case of birds, it is the males who have the double set. So what makes a man? Well in the absence of a definitive test we're back to the subjective. A man is what we agree a man is, and if we can't agree, hey, it's anybody's guess. As Steve McGarrett might say; "We have no idea what it is to be a man... We haven't a clue!