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.
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