Why do birds sing?

Why do birds migrate?

Hunters and gatherers get domesticated.

Do animals remember?

When the kittiwake (Rissa tridactyla) scouts for a new breeding site, it's likely to copy the habitat choices of a successful kittiwake. Photo: Étienne Danchin

Female guppies (Poecilia reticulata) normally prefer bright-colored males. But if young females watch enough dull males succeeding in the breeding department, they too will start to prefer the drabsters. Photo: S. Nordell

Eavesdroppers' heaven: Telephone operators at work in Australia, 1958. Photo: Wolfgang Sievers, Pictorial Collection P2023/18 National Library of Australia.

Curious about the neighbors? Maybe you've learned a thing or two from watching lovers flirting. Maybe you've learned to fish near the other guy's boat.

You could call it eavesdropping. You could call it spying. Or you could get grandiose and call it taking advantage of "public information."

At any rate, it's a talent -- or a curse -- that is supposedly seen only in humans and our fellow primates.

Until now. In a new review, Étienne Danchin, of the National Center for Scientific Research in Paris, and fellow behavioral ecologists have surveyed studies demonstrating that animals are a lot more aware of others than we have assumed.

An animal can learn by observation or trial-and-error. But trial-and-error can be painful and risky. A simple, and perhaps safer, way to get information about potential resources, say the authors, is to watch other animals.

Using this "public information" may reduce risks in unknown situations. For instance, if you're a hungry Norway rat (never know who's poking a snout into Why Files), you could nibble some unfamiliar food and wait to see if it's ratatouille or rat poison. Instead, Danchin writes, Norway rats analyze the breath of other rats to decide if unfamiliar chow is edible. And, while dining, European starlings keep an eye on other starlings, alert to see if others have have found a finer menu.

The new review, published today in Science, shows that animals do use public information in many contexts, ranging from foraging and avoiding predators to choosing a breeding site or a mate.

Animals eavesdrop -- watch how other animals interact -- to learn, say, whether they are good fighters or suitable mates. "In many species," says Danchin, "females prefer the bright male, the showy male, the one with the long tail or the bizarre behavior." These traits, he explains, are costly to produce and indicate genetic fitness.

This mate preference, he notes, is traditionally considered to be written in the genes, "because if you test the females of a particular species, they always prefer the bright male."

But jigger the test a bit, and the results contradict the conventional wisdom, he says. If the same female is shown a dull male mating with a female, and a solitary, bright male, "she will prefer a dull male" when tested a few minutes later.

The experimental situation convinces the female that dull males are better breeders, he says, and thus refutes the idea that genes are the whole explanation for mate choice.

The missing ingredient, he suggests, is "public information that naturally triggers cultural transmission."

The idea that quail or guppies or rats have some sort of culture threatens the conventional wisdom. Culture, after all, is something humans have. We don't have time to enjoy the entire argument here, but behavioral ecologists have been finding plenty of animals with behaviors that are not genetically determined -- such as in the songs of birds and whales, nest site choice, and food preferences.

In the definition used by Danchin and colleagues, culture is "another way to produce variation among populations; it is any pattern that develops and is transmitted non-genetically from one generation to the next." Even though the genes are not involved, "such differences are heritable because they are transmitted through learning."

Many studies cited in the Danchin paper seem to demonstrate that cultural learning, not genetic coding, is a mechanism of inheritance. Just as people who speak French pass French along to their children, other families transmit Swahili. Similarly, songbirds and whales learn different dialects, and pass them along to their offspring.

Most existing studies, Danchin contends, missed the role of culture because they were "done to show that preferences are genetically coded and did not account for the possibility that transmission might be cultural." For example, in many studies of female mate preference, males and females were raised in one cage before the tests. When the females chose a mate, they preferred males that looked like their fathers.

While this is usually interpreted as proving that mating preference is genetically coded, Danchin offers another explanation. "If the females were brought up with their brothers, and the brothers are genetically similar to the fathers, maybe they tend to prefer the same kind of males because they were imprinted to their brothers. Maybe the heredity is due not to genetic transmission but to cultural transmission."

The inheritance of learned behavior is dangerously close to Lamarckian evolution, the discredited idea that traits acquired during life can be inherited by the next generation. (Lamarck eventually became a laughingstock because genes don't work that way. But he was one of the first biologists to realize that organisms do change, so, as Charles Darwin noted, he actually played a major role in evolutionary theory.)

If cultural evolution exists in animals, it would change the direction of heredity. Genetic change must proceed in one direction, from parents to offspring. But if culture plays a role, kids could also be affected by any unrelated adult. Males and females could affect each other.

The new insight, if accepted, represents a revolutionary view of evolution. Danchin and colleagues say the notion of public information helps unravel the role culture may play in animal evolution. "In spite of more than two decades of studies on the potential role of culture in human evolution, animal evolutionary biologists may have given too much importance to genes because they denied the possibility of cultural transmission in animals."

Stay tuned. You can learn a ton by eavesdropping!

Public Information: From Nosy Neighbors to Cultural Evolution, by Étienne Danchin, Luc-Alain Giraldeau, Thomas Valone, Richard Wagner, Science, 23. July 2004.