Population, sperm donation and cheaters

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.

8 responses so far

  • pyrope says:

    Wait, sperm donors have to donate a unique time for each insemination? My biology text book (aka wikipedia) tells me that there are 200 million swimmers per go. Don't they split those guys up?

  • proflikesubstance says:

    I don't know, but I would assume that women buying a sample would prefer a "full load" to a couple of swimmers. There's a reason that many make the trip each time and my impression is that it is not a one shot deal, but rather attempted a few times by the woman.

    But again, I have no expertise here.

  • gerty-z says:

    I'm pretty sure that each donation can be used for multiple tries. The sample is washed and frozen in aliquots that have a defined # of sperm. But definitely less than a "full load". And yes, it generally takes a few tries before you get knocked up. But that is also true if you are using the "in person" delivery system.

  • BLG says:

    I didn't read the article, but the 150 kids from one father and multiple moms represents an AWESOME evolutionary genetics experiment! Think of how much we could learn about heritability, maternal effects, and environmental effects if they all volunteered as a part of a study? That would be so cool!

  • anon says:

    PLS, I am aware of that news story about 150 offspring from one donor. My understanding was that the donor was NOT aware that his sperm would be used for that many offspring. In fact, I thought donors could actually specify how many successful pregnancies they could allow. It's possible that clinics do not need to adhere to the donor's requests beyond anonymity (which is now illegal in some countries - such as Canada).

    There is also a fairly new technology in IVF that has been used in recent years, although I don't see why a recipient would choose this technology in the case of a healthy donor with a high sperm count. This procedure is called intracytoplasmic sperm injection (ICSI), where a single sperm cell is injected into an oocyte for fertilization. This has made it possible for men with an extremely low sperm count to father a child. Otherwise, for "normal" fertilization with IVF, a minimum of 50,000 sperm cells are needed per oocyte. Not much for a guy with a count of say, 50,000,000/ mL.

    Overall, this is a fascinating topic. There was a recent letter in Nature or some journal like that complaining that one article stated that an average sperm count among a population of healthy men was 15,000,000. This is actually considered low and should by no means be considered "normal". The writer was alarmed that sperm counts in general have plummeted since the 30's. Instead of passing this off as normal, we should be worried about why sperm counts and fertility are lower than they used to be.

  • Too bad for the gingers, though...

    Speaking as a half-ginger myself, I think this is very sad.

  • mathdude says:

    As a dude who feels about redheads the way most other guys feel about blondes I find this development shocking!

    🙂

  • YellowSunDress says:

    We need more red heads, not fewer.

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