Guest Blogger: Sarah Webb on Testosterone

We have another blogathon guest blogger today! Sarah Webb is a scientist-turned-writer who has written about subjects including stem cells, the Mars rovers, and her own inability to do a handstand. (She's also the one who pointed me to the dancing cockatoo.) Her work has appeared in Discover, Science News, Scientific American.com, and a variety of other publications.

Ball and stick model of molecule: Structure produced by Ben Mills via Wikipedia


What happens when a former chemist visits a blog ‘bout boys? Her thoughts naturally turn to testosterone. As a woman, I also felt compelled to consult the man in my household on interesting testosterone tidbits. My husband, a fellow science geek, knows all sorts of wacky facts about both the brain and behavior. So here’s a mashup on that hormone that shapes maleness.

Testosterone is built on a stepladder of 3 hexagons and one pentagon like other steroid molecules. The female hormone, estrogen, also has this same basic shape, but also with some changes in the first hexagon on the left.

The Y chromosome instructs a developing male to produce testes. Those testes begin to crank out testosterone. The “default setting” for a developing fetus is to become female, but the waves of testosterone send a chemical signal—“you are male.”

(By the way, women have testosterone, too, made in other parts of the body, including the ovaries. They just have a lot less of it coursing through their veins. Men, boys, you also have estrogen-like hormones, which leads me to. . . .)

Testosterone shapes brain development. Male brains are usually bigger in humans but also have fewer connections binding the two sides together, a structure called the corpus callosum. But a brain doesn’t become male just by marinating in extra testosterone. Actually, the opposite—the testosterone is actually converted to an estrogen-like molecule, first. So the male sex hormone becomes a female hormone in order to etch maleness on the brain.

Isn’t biochemistry kooky sometimes? That puzzle is part of what makes it challenging, fun and truly fascinating.

Want to know more? Check out Sarah's blog at Webb of Science. (Oh yeah -- you'll find me over there today as well. )