Tuesday, December 16, 2008

Wilderness game theory

Above: female lechwe in Botswana. Courtesy of Wikimedia Commons.

There are three things that tickle me about The Economist: fun, safety, and their writers' knack for tying a broad range of topics into the free-market economic theories of Adam Smith.

To wit: this week's issue includes a summary of new research that demonstrates that a rare species of African antelope, the Nile lechwe, is somehow capable of making strategic decisions about whether to give birth to a male or female offspring, depending on its age, in order to maximize the probability of passing on its genes to future generations.

For some as yet unknown reason (possibly because sons are generally heavier), lechwe are three times more likely to die in childbirth while delivering a son than they are while delivering a daughter. So giving birth to a son is a risky proposition for a lechwe. It's also more of a genetic gamble: a male lechwe has some chance of becoming dominant and breeding a lot, which could be a genetic jackpot, but if a male fails to become dominant, it becomes a genetic dead-end. Daughters, on the other hand, are the safer bet, since nearly all females breed and will pass on some of your genes to another generation.

In theory, if a mother could somehow choose between sons and daughters, a lechwe should choose to give birth to more daughters while she's young, then take a chance on a son or two once they're old and expect to die soon anyhow. If possible, the mother should also put in more resources into making sure that her offspring are larger as she gets older, so that if she does give birth to a male, it has a better chance of becoming dominant.

It's more or less the same strategy that explains the old Publishers' Clearinghouse Sweepstakes contests and their demographics. The Sweepstakes take up a lot of time and postage, and the odds of payout are so low that most young or working people couldn't be bothered by it [if you doubt the demographics, how do you explain Ed McMahon's spokesmanship and the fact that the ads always ran among pitches for Metamucil and adult diapers?]. But if you're old, retired, and have nothing better to do with your time, why not buy crappy paperback novels you don't want and spend hours at the post office? After all, you could win ten million dollars!

Of course, a variable reproductive strategy would assume that lechwe are capable of dynamic optimization, a complicated subdiscipline of economics that utilizes multivariable calculus. But as it turns out, lechwe somehow are capable of changing and optimizing their reproductive strategy as they age.

Researchers at the San Diego Zoo's 90-acre Wild Animal Park witnessed the birth of over 176 lechwe calves over a 38-year period. They found that yearling lechwes had sons 57% of the time, but by the time those mothers became seven years old (roughly middle age for a lechwe, whose average lifespan is 12 years) the odds of having a son rises to 67%.

Not only that, but older mothers are more likely to give birth to larger offspring as well.

Lechwe probably aren't capable of making a conscious choice between male and female offspring, the way humans might choose between small-cap and fixed-income IRAs. But the dependence of their reproductive strategy on age does indicate that the lechwes' reproductive strategy is the product of evolution: females who are more likely to give birth to males later in life are more likely to pass their genes on to future generations; therefore, after thousands of generations of lechwes, most females somehow possess this unusual reproductive characteristic.

With some imagination, an alternative solution to our credit crisis presents itself: let humans breed for a few dozen more generations, and the surviving offspring of our most fertile and successful money managers will be able to solve our financial problems with ease.

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