You're in a new town for the night and looking for a bite to eat. Walking down Main Street, you see a couple possibilities: a crowded diner and a nearly empty hamburger joint. Which do you choose?
Eating preferences aside, chances are you would choose the crowded diner. Psychologists, economists and advertisers have long shown that people make decisions largely based on what others do. But what if the newcomer were a rat, not a person? And the choice in question was between two piles of rotting garbage?
It turns out non-human animals, too, make decisions based on watching each other. Norway rats, for example, smell the scent of foods recently eaten on the whiskers and fur of other rats and base their meal choice on these odors. Birds, meanwhile, such as starlings and red crossbills, watch their neighbors when looking for prey. If others are having success in a particular patch, they'll stick around. If not, they try their luck elsewhere.
Etienne Danchin of the Pierre and Marie Curie University in Paris argues in the current issue of Science that the use of so-called public information is widespread in the animal kingdom and may lead to the development of a kind of culture within animal species that, in turn, affects evolution.
"Social information is a big thing for animals when making decisions," said Thomas Valone, a biologist at St. Louis University and coauthor of the study. "We're saying it's another piece of information that biologists should pay attention to when we try to understand evolution."
Eating isn't the only area where animals appear to take cues from one another. Other research shows social information is also important when animals are choosing where — and who — to mate.
Studies of antelopes, for example, suggest that females base their selection of breeding sites on the smell of other female antelope's urine in the soil.
When scientists transplanted soil from successful mating territories to less successful ones, female antelopes new to the areas always chose the territories with soil scented with successful females — regardless of the location.
"There is apparently something in the urine of successful mating females that others pick up," said Valone.
When it comes to choosing mates, following others' mate choices sometimes takes priority.
Female guppy fish, for example, normally choose the most brightly colored males for mating. Evolution theory explains this preference this way: Brightly colored fish are more vulnerable to predators, so any brightly colored males around must be especially fit and adept at avoiding being eaten and therefore good dad material.
But this rule of thumb changes when female guppies observe other females choosing duller colored males.
In experiments, female guppies were placed in glass tanks where they could see another female guppy in adjacent tanks giving a dull colored male more attention than a brightly colored one (the observer could not realize this was because the brightly colored one was sequestered in a separate tank).
When the female observer was then placed in a tank with both the dull and brightly colored males, the female nearly always chose the dull-colored one — since this was the one she saw cavorting with the other female.