This Gender Mystery Starts Nine Months Before Birth - Issue 27 : Dark Matter
▻http://nautil.us/issue/27/dark-matter/this-gender-mystery-starts-nine-months-before-birth
Is it a boy or a girl? That’s what everyone wants to know from the expecting parents. The ratio of newborn boys to girls (called the secondary sex ratio) is a matter of social importance and, occasionally, even national policy. But there is another ratio that, despite being more obscure, is just as important: The ratio of boys to girls at conception, when the egg is fertilized and development begins, called the primary sex ratio. While the secondary sex ratio is consistently about 106 boys for every 100 girls (or, just 106 for shorthand), the primary sex ratio has been a subject of persistent speculation over the centuries. Naïvely one might expect it to be 100—balanced, equal numbers of boys and girls. To see why it has attracted such attention, suppose it were 125 instead. Since the (...)