Live sharp, die young.

Something that doesn't feel quite like skiving on a slow Friday afternoon is browsing a few journals for bloggable papers. Here's one. It concerns a question that vexes the best of us: Why are animals so bloody stupid?



Learning to find good things and avoid bad things is useful - there's a Statement of the Bleedin' Obvious for you - but many animals aren't as good at it as they could be. We can tell this using selection experiments: in a variety of species, if you let only fast learners breed, the population gets better at learning.

As it happens, those experimental results are almost as bleedin' obvious to biologists as the first bit. Selection experiments usually do work, because... well, because Darwin was right. Most species are genetically variable, and most traits have at least some heritable component, so selection is a powerful force. You can't beat bacteria for really long-term studies, but when it comes to animals, it's usually fruit flies as ever. In laboratories around the world you can find clever flies, long-lived flies, sexually insatiable flies, alcohol-tolerant flies, alcohol-susceptible flies (carrying a mutation called cheap date), and magnificent flying aces selected for their determined zooming down a wind tunnel. You can choose a tiny and seemingly insignificant character to select on if you like, and and that works too. It's publishably interesting, and requires a decent explanation, when a properly done selection experiment doesn't make a difference.

Here's the problem: if learning is advantageous, why aren't wild fruit flies already as clever as the selected ones in the lab? Is a fruitfly intellectual looked down upon as a nerd by potential mates, or targeted by secret police as a threat to the state, or is she merely prone to existential despair? Burger et al. tackled this problem with the aid of a batch of smartarse flies that could learn to avoid bitter fruit jellies. There's a chance this would instead select for flies with a particularly good sense of smell, but they checked for that.

It seemed that the smartarse flies were indeed at a subtle evolutionary disadvantage, i.e. they dropped dead. The lifespan of females - the selection had only been on female learning ability - was down by 15%, and that of males by 10%.

Now, a potential snag with this is that populations under selection are a bit inbred - necessarily, because fewer flies are having offspring - and that might make them sickly. However, in all the replications of this experiment, it was only lifespan that was affected, not body size or fecundity or any of the other usual problems with inbreeding. And finally, the authors also tested some of the long-lived flies I mentioned above. Those flies were, indeed, unusually stupid. This strongly suggests that there's a trade-off in flies between living longer and being brighter. In the wild, at the moment, living longer is a better strategy - and so the little dimwits know no better than to fly straight into your glass of sauvignon blanc and drown. Sad, but true.

(There are probably genetic trade-offs in humans as well, but they're very unlikely to be precisely the same ones as in fruit flies! So although a simplistic reading might cause understandable concern, do rest easy: this research does not imply that George W. Bush will live forever.)

Joep M. S. Burger, Munjong Kolss, Juliette Pont, Tadeusz J. Kawecki (2008) LEARNING ABILITY AND LONGEVITY: A SYMMETRICAL EVOLUTIONARY TRADE-OFF IN DROSOPHILA. Evolution 62 (6), 1294–1304.