Do men determine the sex of their babies? This question is a little more complicated than the old "XX, XY" scenario. We've long known that the father supplies the sex of the baby to be in his sperm by providing either an additional X or Y chromosome. But, it turns out, the daddy may be responsible for keeping the population unbalanced with too many of either sex. How is this possible, you ask? Well, I'll tell you:

Ghastly as it sounds, it is believed a lot of males are lost to war and a lot of females are lost to selective abortion in certain cultures. According to researcher Corry Gellatly of Newcastle University, men contain a gene that decides whether they will father more males, females or an even number of each. (Women contain the gene as well but it remains unexpressed.) Allegedly the gene makes them more likely to attract a mate and father daughters when females are in short supply, and more likely to father males when men are in short supply.

Gellatly reviewed the family trees of nearly 1,000 North Americans and Europeans and created a computer simulation of how his gene would affect gender outcome over 500 generations. The results from the actual family trees and the computer simulations were the same. According to his hypothesis, the gene is expressed as either male/male that produces more sperm that leads to males; female/male which leads to a 50/50 chance of either sex; or a female/female that leads to making more little girls. Gellatly is quick to point out that while this gene would make a stronger case for a male or female offspring, the mother does contribute something to the gene which "dilutes" it. Thus, the pattern caused by the gene is a subtler one.

Hmm. Interesting indeed. Makes me wonder, though, if this isn't just another step toward some creepy Brave New World thing where people get to choose the sex of their babies!