Fruit Flies and Foresight; or, Evolution for Dummies
By Bryan Caplan
A common objection to hereditarian theories of intelligence is that “Intelligence is SO important, evolution would have eliminated genetic variation.” A simple fruit fly experiment (discussed in newscientist.com) shows how wrong this is:
The team first bred a group of fast-learning flies. They allowed fruit flies to lay eggs on gels flavoured with either orange or pineapple juice. But one or the other was also spiked with bitter quinine. The next time round the flies were given the juice only – but some remembered which had previously been laced with quinine and laid their eggs on the other flavour…
After 20 generations, most flies from the selected line could learn the task in one go. They were not just better at tasting different juices or more averse to quinine, as ordinary flies could eventually learn to avoid the sabotaged flavour too, but it took them three to five sessions…
However, when the larvae of the more astute flies were made to compete with ordinary larvae for scarce food, fewer of them survived.
“They are slower at feeding,” says Mery. He speculates that the flies may have to invest more energy in making or re-arranging connections between neurons in their brains, leaving them with less energy to forage when calories are limited.
Now I’ve never noticed that smart human beings are slower at feeding. But there is an obvious evolutionary drawback to human intelligence, too. Namely: Smart people are, almost by definition, more foresighted, which in turns leads to more responsible sexual behavior, and thus fewer children. In the National Longitudinal Study of Youth, for example, a linear estimate says that the most intelligent respondents have .88 more children than the least intelligent. Foresight has a lot of evolutionary advantages, but it’s not a free lunch.
Of course, if you’re really, really smart, you will be convinced by my argument that it is selfishly optimal to have more kids!