When nature maximizes survival under constraint, learning is just another parameter in the equation:
Lots of Animals Learn, but Smarter Isn’t Better, by Carl Zimmer, NY Times: ...Learning ... turns out to have dangerous side effects that make its evolution even more puzzling. Dr. Kawecki and his colleagues have produced striking evidence for these side effects by studying flies as they evolve into better learners in the lab.
To produce smarter flies, the researchers present the insects with a choice of orange or pineapple jelly to eat. Both smell delicious to the insect. But the flies that land on the orange jelly discover that it is spiked with bitter-tasting quinine. The flies have three hours to learn that the nice odor of oranges is followed by a nasty taste.
To test the flies, the scientists then present them with two plates of jelly, one orange and one pineapple. This time, neither has quinine. The flies settle on both plates of jelly, feed, and the females lay their eggs.
“The flies that remember they had a bad experience with orange should continue to avoid orange and go to the pineapple,” Dr. Kawecki said.
Dr. Kawecki and his colleagues collect the eggs from the quinine-free pineapple jelly and use them to produce the next generation of flies. The scientists repeat the procedure on the new flies, except that the pineapple jelly is spiked with quinine instead of the orange.
It takes just 15 generations under these conditions for the flies to become genetically programmed to learn better. At the beginning of the experiment, the flies take many hours to learn the difference between the normal and quinine-spiked jellies. The fast-learning strain of flies needs less than an hour.
But the flies pay a price for fast learning.
Dr. Kawecki and his colleagues pitted smart fly larvae against a different strain of flies, ... giving them a meager supply of yeast to see who would survive. ... About half the smart flies survived; 80 percent of the ordinary flies did.
Reversing the experiment showed that being smart does not ensure survival. “We took some population of flies and kept them over 30 generations on really poor food so they adapted so they could develop better on it,” Dr. Kawecki said. “And then we asked what happened to the learning ability. It went down.”
The ability to learn does not just harm the flies in their youth, though... fast-learning flies live on average 15 percent shorter lives... Flies that have undergone selection for long life were up to 40 percent worse at learning than ordinary flies.
“We don’t know what the mechanism of this is,” Dr. Kawecki said. One clue comes from another experiment, in which ... the very act of learning takes a toll. The scientists trained some fast-learning flies to associate an odor with powerful vibrations. “These flies died about 20 percent faster than flies with the same genes, but which were not forced to learn,” he said. ...
Dr. Dukas argues that learning evolves to higher levels only when it is a better way to respond to the environment than relying on automatic responses.
“It’s good when you want to rely on information that’s unique to a time and place,” Dr. Dukas said. Some bee species, for example, feed on a single flower species. They can find plenty of nectar using automatic cues. Other bees are adapted to many different flowers, each with a different shape and a different flowering time. Learning may be a better strategy in such cases. ...
Dr. Kawecki suspects that each species evolves until it reaches an equilibrium between the costs and benefits of learning. His experiments demonstrate that flies have the genetic potential to become significantly smarter in the wild. But only under his lab conditions does evolution actually move in that direction. In nature, any improvement in learning would cost too much. ...