The July 29 issue of Science had a special section (paywall) devoted to the changing global population dynamics that showed regional trends and predicted growth patterns over the next 10-15 years. It's a fairly fascinating (and semi-alarming) collection of articles and commentaries that is worth a read. As someone who has just added one more individual to the global population, I was particularly struck by a figure that reported the number of children that families in different areas of the world considered "ideal".
Obviously there are a lot of factors that play into this decision, but I was intrigued that even across Africa, the numbers ranged from 9.1 in Niger to 3 in Egypt. Whereas number from North America were not reported, both the US and Canada average 1.5-2.1 births per woman. It shouldn't be surprising then, that projections for population growth between 2010 and 2050 in North American (and both Europe and Latin America) are dwarfed by that of Africa (and Asia) by an order of magnitude. On average, North Americans just don't have a lot of kids.
But in nature, every system has cheaters - those who exploit the constraints that most in the population live by in order to carve out an advantage for themselves. This is why a pair of recent news stories about sperm donation caught my attention. Only a few years ago it was essentially impossible to trace the number of kids that a individual sperm donor produced. But on 2000 donorsiblingregistry.com was founded, allowing people to self-identify as donors or children of donors. Although not a complete picture, what the site did show was the potentially enormous population-level effect of sperm donation. In one case, a currently anonymous donor has fathered at least 150 children who have signed onto the site and in another, a man who has allowed contact is now the father of at least 70 children from across the country by the age of 33. Two men, 220 children... and climbing.
Judging at least from the story on the man with 70 children, fathering that many kids was not something he anticipated. How could he? And while he has undoubtedly brought a lot of happiness to the women who could not otherwise conceive, I can't possibly imagine how that is going to complicate his life in the future. But at the same time, the evolutionary biologist in me has to marvel at the reproductive fitness of these guys. Not only are they acting under r selection, but they got paid $150 per donation*.
I am not versed in the pros and cons of sperm donation, nor is it something I would ever consider doing, but the potential for leaving one's genetic mark is slightly mind-blowing. Better become friends with your local post office Mr. Siesler, because that is a shit-load of birthday cards.
*Even a conservative estimate of 200 donations yields $30,000.