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ANDREA SEABROOK, host:

From NPR News, this is ALL THINGS CONSIDERED. I'm Andrea Seabrook.

A piece in the New York Times caught our eye this week. The author, Verlin Klickenborg(ph), was musing on an earlier report in the paper about fruit fly experiments. Those experiments showed that smarter fruit flies died younger than flies that didn't learn. Mr. Klickenborg wanted to know is there an adaptive value to limited intelligence or, as he wrote, is there a biological cost of our own intelligence?

Now, that is science way out of the box.

(Soundbite of music)

SEABROOK: The man behind the fruit fly experiment is Tadeusz Kawecki. He's an evolutionary biologist at the University of Lausanne in Switzerland. Thanks for being with us, professor.

Professor TADEUSZ KAWECKI (Evolutionary Biologist, University of Lausanne): Good afternoon.

SEABROOK: So, let me ask you this: fruit flies that learn don't live longer, they live shorter lives. Did that surprise you?

Prof. KAWECKI: Well, it didn't surprise me exactly because we have seen before that those flies that learn better are inferior in terms of competition for highly limited food. So there are apparently evolutionary tradeoffs involved. And that presumably reflects some kind of cost of their investing in the development and maintenance and the function of their brain.

SEABROOK: So there's a cost to intelligence?

Prof. KAWECKI: Well, that's how we interpret this, yes.

SEABROOK: Doesn't this run counter to what we've been taught about evolution? I mean, don't animals that learn and adapt generally live longer, they're more fit?

Prof. KAWECKI: Well, learning, being able to modify your behavior in response to novel situations is certainly advantageous in many cases. We are looking at learning and the ability to learn, having the machinery to learn well, as an investment that an animal makes. So, the returns from this investment in terms of being able to better survive when the environment changes, et cetera, have to be weighted against the potential costs.

SEABROOK: So, when an animal is in the wild, how is the ability to learn helpful?

Prof. KAWECKI: Well, it can be helpful if the environment changes. So, you can imagine for a fruit fly the world is composed of odors and colors and patterns. So, say, odor A always leads to good food and odor B leads to a bad place, dangerous, whatever. You don't need learning ability. Avoidance of odor B can be wired in genetically.

SEABROOK: Instinct.

Prof. KAWECKI: Like instinct, exactly. In contrast, if odor A sometimes means food and sometimes means something bad and vice versa for odor B, it pays to learn, because you can benefit from gathering information and benefit from experience.

SEABROOK: And how is that ability to learn harmful in the wild?

Prof. KAWECKI: Now, this can be answered at two levels. At one level, it might still be good but not good enough to compensate for energetic costs of having a big brain. For example, if you have a big brain and food becomes scarce, and it's so scarce that your big brain does not help you to find it, you might be the first one to die because you need more energy to keep your brain functioning.

SEABROOK: Um-hum.

Prof. KAWECKI: At another level you can say that even the act of learning itself might not be very useful. So imagine that you're an antelope and rather than having an instinctive fear of a lion, you are trying to learn about it. Is lion nice or is the lion maybe neutral or is it maybe dangerous?

SEABROOK: You'll find out pretty quick.

Prof. KAWECKI: Right. But it will be too late. So, relying on learning will not pay if the cost of making a mistake is too high.

SEABROOK: Mr. Kawecki, can you extrapolate this to humans at all?

Prof. KAWECKI: Well, at some level we can. It's clear that in humans a relationship between longevity and learning, there has been an increase both in intelligence and in life span. So we're both smarter and live longer than our nearest relative, the chimpanzees.

On the other hand, we can make sort of educated guesses about costs that our huge brains and our oversized intelligence has cost.

SEABROOK: Um-hum.

Prof. KAWECKI: For example, in pre-industrial conditions, death at childbirth was a significant source of mortality for women. And this would seem kind of strange for a natural process. Well, the reason, at least in part, is because the head of a human baby is so huge...

SEABROOK: Yeah.

Prof. KAWECKI: ...because it contains this huge brain, which is difficult. Despite that, the human babies are still born very underdeveloped. If we compare a newborn human to a newborn chimpanzee, there's a huge difference. A newborn human is totally helpless for several months, whereas a newborn chimpanzee can cling to his mother within a few days, which allows the mother to move around much more freely and gather food, et cetera.

SEABROOK: Yeah, I've read that human babies in fact are born too early in some ways.

Prof. KAWECKI: Right. That's exactly the point. Now, despite of that - the time for which the human offspring are dependent on their parents is, again, a record in the animal kingdom. We are so dependent on learning, accumulating all the information that it takes so much time that we have to stay with our parents for maybe under natural conditions, say, pre-industrial conditions, it was, you know, 15 years or so.

And in the modern society, at least in Switzerland, it may go for 30, you know.

(Soundbite of laughter)

SEABROOK: Tadeusz Kawecki is an evolutionary biologist at the University of Lausanne in Switzerland. Thanks very much for speaking with us.

Prof. KAWECKI: Thank you.

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