Laying in bed the other morning unable to get back to sleep, I kept pondering the randomness of a baby’s gender. Is it really a random 50/50 possibility either way? After all, the world population isn’t exactly even ( 3,477,829,638 men to 3,418,059,380 women in 2010, according to The Internet). And a lot of families with more than one child seem skewed to one gender or another, almost as if they couldn’t have children of the other gender if they tried.
So I used my parents large families as an example. On the liquid marker board on my wall, I plotted the older generation of each family vertically and connected each of their bubbles horizontally to the bubbles representing their children. Below, I redrew the bubbles and flipped a coin for each one and recorded each coin tosses’ outcome by coloring each bubble either red or blue. Viewed in the aggregate, the results look strikingly similar. (The only 50/50 split come from my cousins on my mom’s side. Out of three sisters, one had two girls, the other a boy and a girl, while my mom had two boys.)
This also reveals something about probability that has isn’t exactly obvious: that a 50/50 chance doesn’t necessarily yield an even distribution of outcome in real life.
For more information, check out Wikipedia’s page on Human Sex Ratio.