Brainpower can be a bad thing 鈥� at least if you鈥檙e a fruit fly. Brainier flies live shorter lives than dumb ones, a finding that backs up the theory that intelligence comes at a cost.
Tadeusz Kawecki, an evolutionary biologist at the University of Lausanne, Switzerland, and his colleagues taught flies to associate a chemical scent with an unpleasant experience 鈥� a violent shaking of their test-tube home 鈥� and then bred the best learners. Over time, they created a line of flies that were much better at the task. Three years ago, Kawecki鈥檚 team showed that these smarter flies died more quickly when deprived of food and water.
Now, a new experiment by Kawecki鈥檚 associate Joep Burger has found that the smart flies鈥� lifespans were about 15 per cent shorter than normal flies under standard conditions. What鈥檚 more, when the team tested a second line of flies bred for increased lifespan, they found that when young, these long-lived flies were about 40 per cent worse at learning than normal flies (Evolution, ).
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鈥淪mart flies鈥� lifespans were 15 per cent shorter than normal flies, and long-lived flies were about 40 per cent worse at learning鈥�
This 鈥渃ost of intelligence鈥� presumably reflects the greater energy cost to the flies of producing and maintaining a larger, more powerful brain, Kawecki speculates.
The trade-off between learning and longevity is unlikely to apply to humans, who have evolved to be both unusually long-lived and highly intelligent, says Kawecki. Instead, the cost of learning may show up in other ways, such as the difficulty of giving birth to such large-headed offspring.
In flies and some other animals, the negative effect of longevity on learning ability may be more a laboratory artefact than a real-world phenomenon, says Reuven Dukas, an animal behaviourist at McMaster University in Hamilton, Ontario, Canada.
鈥淚t鈥檚 not intuitive at all that you would select for longevity and it would result in lesser learning,鈥� says Dukas. 鈥淭here is more to learn if you live longer.鈥�
Evolution 鈥� Learn more about the struggle to survive in our comprehensive special report.
