Blog Post

Evolution for the Rest of Us (FINALLY!)

FINALLY. This is the study by an evolutionary biologist that I've beenwaiting for, one that does not begin from the assumption that humansare the be-all and end-all of evolution nor that what humans think of(and the tiny bit we know about) human "intelligence" is the raisond'etre of evolution, even within homo sapiens. Theorists have made this point but it is a rare experimental scientist who reverses the equation and the teleologies.  So much of what passes for evolutionary biology is the most presentist kind of argument, with intelligence defined by abilities, such as reading, which have only been around for a fraction of human existence. So much of what passes for evolutionary biology is based on the most Euro-centric assumptions about what "intelligence" is, what it "means to be human" is. The circularity, post E. O. Wilson, of too much evolutionary biology does a disservice to good science and to evolution as a theoretical and scientific construct.

 

Carl Zimmer of the NYTimes reports on Tadeusz Kawecki's excellent work which begins by asking(FINALLY, again), "If it's so great to be smart, why have most animalsremained dumb." Duh. Readers of this blog know that I've beenflogging this one for a long time . . . but it's nice to have adistinguished evolutionary biologist working from this side of theequation.

 

 

 

New York Times,

May 6, 2008

Lots of Animals Learn, but Smarter Isn?t Better

?Why are humans so smart?? isa question that fascinates scientists. Tadeusz Kawecki, an evolutionarybiologist at the University of Fribourg, likes to turn around thequestion.

?If it?s so great to be smart,? Dr. Kawecki asks, ?why have most animals remained dumb??

Dr. Kawecki and like-minded scientists are trying to figure out whyanimals learn and why some have evolved to be better at learning thanothers. One reason for the difference, their research finds, is thatbeing smart can be bad for an animal?s health.

Learning is remarkably widespread in the animal kingdom. Even themicroscopic vinegar worm, Caenorhadits elegans, can learn, despitehaving just 302 neurons. It feeds on bacteria. But if it eats adisease-causing strain, it can become sick.

The worms are not born with an innate aversion to the dangerousbacteria. They need time to learn to tell the difference and avoidbecoming sick.

Many insects are also good at learning. ?People thought insects werelittle robots doing everything by instinct,? said Reuven Dukas, abiologist at McMaster University.

Research by Dr. Dukas and others has shown that insects deserve morerespect. Dr. Dukas has found that the larvae of one of the all-timefavorite lab animals, the fruit fly, Drosophila melanogaster, couldlearn to associate certain odors with food and other odors withpredators.

In another set of experiments, Dr. Dukas discovered that young maleflies wasted a lot of time trying to court unreceptive females. Ittakes time to learn the signs of a receptive fly.

Dr. Dukas hypothesizes that any animal with a nervous system canlearn. Even in cases where scientists have failed to document learningin a species, he thinks they should not be too quick to rule it out.?Is it because I?m not a good teacher or because the animal doesn?tlearn?? Dr. Dukas asked.

Although learning may be widespread among animals, Dr. Dukas wonderswhy they bothered to evolve it in the first place. ?You cannot just saythat learning is an adaptation to a changing environment,? he said.

It is possible to adapt to a changing environment without using anervous system to learn. Bacteria can alter behavior to help theirsurvival. If a microbe senses a toxin, it can swim away. If it senses anew food, it can switch genes on and off to alter its metabolism.

?A genetic network like the one in E. coli is amazingly good in changing environments,? Dr. Dukas said.

Learning also turns out to have dangerous side effects that make itsevolution even more puzzling. Dr. Kawecki and his colleagues haveproduced striking evidence for these side effects by studying flies asthey evolve into better learners in the lab.

To produce smarter flies, the researchers present the insects with achoice of orange or pineapple jelly to eat. Both smell delicious to theinsect. But the flies that land on the orange jelly discover that it isspiked with bitter-tasting quinine. The flies have three hours to learnthat the nice odor of oranges is followed by a nasty taste.

To test the flies, the scientists then present them with two platesof jelly, one orange and one pineapple. This time, neither has quinine.The flies settle on both plates of jelly, feed, and the females laytheir eggs.

?The flies that remember they had a bad experience with orangeshould continue to avoid orange and go to the pineapple,? Dr. Kaweckisaid.

Dr. Kawecki and his colleagues collect the eggs from thequinine-free pineapple jelly and use them to produce the nextgeneration of flies. The scientists repeat the procedure on the newflies, except that the pineapple jelly is spiked with quinine insteadof the orange.

It takes just 15 generations under these conditions for the flies tobecome genetically programmed to learn better. At the beginning of theexperiment, the flies take many hours to learn the difference betweenthe normal and quinine-spiked jellies. The fast-learning strain offlies needs less than an hour.

But the flies pay a price for fast learning. Dr. Kawecki and hiscolleagues pitted smart fly larvae against a different strain of flies,mixing the insects and giving them a meager supply of yeast to see whowould survive. The scientists then ran the same experiment, but withthe ordinary relatives of the smart flies competing against the newstrain. About half the smart flies survived; 80 percent of the ordinaryflies did.

Reversing the experiment showed that being smart does not ensuresurvival. ?We took some population of flies and kept them over 30generations on really poor food so they adapted so they could developbetter on it,? Dr. Kawecki said. ?And then we asked what happened tothe learning ability. It went down.?

The ability to learn does not just harm the flies in their youth,though. In a paper to be published in the journal Evolution, Dr.Kawecki and his colleagues report that their fast-learning flies liveon average 15 percent shorter lives than flies that had not experiencedselection on the quinine-spiked jelly. Flies that have undergoneselection for long life were up to 40 percent worse at learning thanordinary flies.

?We don?t know what the mechanism of this is,? Dr. Kawecki said.

One clue comes from another experiment, in which he and hiscolleagues found that the very act of learning takes a toll. Thescientists trained some fast-learning flies to associate an odor withpowerful vibrations. ?These flies died about 20 percent faster thanflies with the same genes, but which were not forced to learn,? he said.

Forming neuron connections may cause harmful side effects. It isalso possible that genes that allow learning to develop faster and lastlonger may cause other changes.

?We use computers with memorythat?s almost free, but biological information is costly,? Dr. Dukassaid. He added that the costs Dr. Kawecki documented were not smartanimals? only penalties. ?It means you start out in life beinginexperienced,? Dr. Dukas said.

When birds leave the nest, they need time to learn to find food andavoid predators. As a result, they are more likely to starve or bekilled.

Dr. Dukas argues that learning evolves to higher levels only when itis a better way to respond to the environment than relying on automaticresponses.

?It?s good when you want to rely on information that?s unique to atime and place,? Dr. Dukas said. Some bee species, for example, feed ona single flower species. They can find plenty of nectar using automaticcues. Other beesare adapted to many different flowers, each with a different shape anda different flowering time. Learning may be a better strategy in suchcases.

Scientists have carried out few studies to test this idea. Onestudy, published this year by scientists at the University of London,showed that fast-learning colonies of bumblebees collected up to 40percent more nectar than slower colonies.

Dr. Kawecki suspects that each species evolves until it reaches anequilibrium between the costs and benefits of learning. His experimentsdemonstrate that flies have the genetic potential to becomesignificantly smarter in the wild. But only under his lab conditionsdoes evolution actually move in that direction. In nature, anyimprovement in learning would cost too much.

Dr. Kawecki and Dr. Dukas agree that scientists need to pinpoint thetradeoffs, and they will have to gauge the role of learning in thelives of many species. As their own knowledge increases, they willunderstand more about humans? gift for learning.

?Humans have gone to the extreme,? said Dr. Dukas, both in theability of our species to learn and in the cost for that ability.

Humans? oversize brains require 20 percent of all the caloriesburned at rest. A newborn?s brain is so big that it can create seriousrisks for mother and child at birth. Yet newborns know so little thatthey are entirely helpless. It takes many years for humans to learnenough to live on their own.

Dr. Kawecki says it is worth investigating whether humans also payhidden costs for extreme learning. ?We could speculate that somediseases are a byproduct of intelligence,? he said.

The benefits of learning must have been enormous for evolution tohave overcome those costs, Dr. Kawecki argues. For many animals,learning mainly offers a benefit in finding food or a mate. But humansalso live in complex societies where learning has benefits, as well.

?If you?re using your intelligence to outsmart your group, thenthere?s an arms race,? Dr. Kawecki said. ?So there?s no absoluteoptimal level. You just have to be smarter than the others.?

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