When It Pays To Be Dumb

Intelligence is no different than feathers or tentacles or petals. It’s a biological trait with both costs and benefits. It costs energy (the calories we use to build and run our brains) which we could otherwise use to keep our bodies warm, to build extra muscle, to ward off diseases. It’s also possible for the genes that enhance one trait, such as intelligence, to interfere with another one, or even cause diseases. Over the course of evolutionary time, a trait can vanish from a population if its cost is too high.

On the other hand, intelligence may offer some evolutionary benefits, by allowing us to find food, withstand the elements, locate the car keys our children have put in their dollhouses, etc. But it is by no means a given that intelligence is always a net plus. It all depends on the conditions in which we–and other animals–find ourselves in.

Scientists have come to appreciate how optional intelligence is through several sorts of experiments. Last year French scientists reported an experiment in which they bred fruit flies for their ability to learn. They would give the flies oranges and pineapples on which to lay their eggs, but they would dab one kind of fruit with a nasty tasting chemical. Some of the flies learned quickly to avoid the bad-tasting fruits, avoiding them even when the researchers didn’t put the chemicals on them. These smarter flies were allowed to reproduce, passing on their learning genes to the next generation. (The researchers switched the bad taste between the fruits in each generation to make sure that the flies weren’t simply evolving a distaste for oranges or pineapples.) This line of flies became significantly better at learning than their unevolved cousins in a few dozen generations. And in a reverse experiment, they succeeded in breeding stupid flies who did worse at learning than normal flies.

If it was so easy for the scientists to produce better learning in flies, why hadn’t the ancestors of these insects already evolved this sort of intelligence in the wild? The answer is that this intelligence comes at a cost. The researchers put the larvae of the smart flies alongside some normal fly larvae and let them compete for a supply of yeast. They then counted how many of the larvae survived to adulthood. Then they did the same experiment with the dumb flies. They found that the larvae of smart flies are more likely to die off than the dumb ones.

Now comes another experiment in intelligence, this one conducted mainly by nature rather than scientists. Many of the streams that feed the Panama canal are inhabited by the same species of guppy, Brachyraphis episcopi. And in many of these streams, the guppies live in two different habitats: above and below waterfalls. Below the waterfalls, they face a lot of competition from other fish that are trying to eat the fruit and other foods that fall from the trees overhead, and they also have to cope with several predatory fish. But above the waterfalls the guppies enjoy a predator free existence. Researchers at the University of Edinburgh realized that this arrangement created excellent conditions for the evolution of different kinds of behavior within a species. Upstream guppies would not face the same evolutionary pressures that the downstream fish were. And if the researchers were right, they should find the pattern repeated in stream after stream.

The researchers netted guppies from four different streams, both from upstream and downstream populations. They then shipped the fish back to their lab in Scotland and tested their ability to make their way through mazes to find food. As they report in a paper in press at Behavioral Ecology, the fish from the low-predator upstream sites consistently outperformed their downstream counterparts. They figured out the mazes twice as quickly.

The researchers argue that the upstream fish do so well because they have been able to evolve a sort of single-mindedness. In the wild, the guppies appear to size up their stream and figure out the best place to wait for food to drop to the water. They head for that patch quickly and defend it from other guppies. This sort of learning translates well into a laboratory maze. The downstream guppies, on the other hand, would risk becoming easy prey if all they did were to search for the best patch of stream. Instead, they also have to get a better sense of their overall habitat, spotting predators, finding refuges, and so on. In the laboratory, they tended to explore more of the passageways of the maze than the upstream guppies, perhaps due to their instinct to get a lay of the land (or perhaps the lay of the water).

These results raise a sticky point about ourselves. They suggest that different populations of the same species (such as humans) can evolve differences in cognition in response to different environments. I don’t think these results can be used to boost any notion of race-based difference in IQ, though, because we’re not fish or laboratory fruit flies. I don’t think the conditions that people in different parts of the world face are as different as these flies and guppies have faced. The most important lesson from these results, I think, is make us tone down our self-love a bit. Being intelligent does not make us superior to other animals. It only makes us superior in one respect.