Tool–Using Dolphins

The June 9 Economist had a fascinating story about culturally transmitted tool use among dolphins.

A group of researchers led by Michael Krützen, of the University of New South Wales in Sydney, has found that the bottlenose dolphins of Shark Bay in Western Australia like to mop up their food with sponges (above and below), and that they learn the trick from their mothers.

Here's the article.

Mother Knows Best

Culture in the ocean depths

There was a time when the ability to make and use tools was regarded as a purely human trick.

So was the possession of culture—that is, the ability of individuals to learn patterns of behaviour from others and, eventually, to pass them down the generations.

This anthropocentric view of the world is long gone in zoological circles.

The manufacture and use of tools has been observed in many species (chimpanzees "fishing" for termites using specially prepared twigs, for example).

So has the transmission of ideas (washing food in the sea to get rid of sand grains, by Japanese monkeys).

And indirect evidence from chimps suggests that tool use itself is culturally transmitted, with different groups having different cultural traditions.

But now a group of researchers led by Michael Krützen, of the University of New South Wales, in Sydney, has found evidence of culturally transmitted tool use under the sea.

The bottlenose dolphins of Shark Bay in Western Australia, it seems, like to mop up their food with sponges, and they learn the trick at their mother's flipper.

Or, rather, some of them do.

The animals in question break off bits of sponge, cover their beaks with them, and probe the sea floor for fish.

Whether the sponge aids the probing, or merely makes it more comfortable, is not clear.

But what is clear from Dr Krützen's study, published in the Proceedings of the National Academy of Sciences, is that the sponge-using dolphins are related to one another.

They all share the same mitochondrial DNA, a type of DNA transmitted to offspring only from their mothers.

All seem, therefore, to be descended from the same female.

Moreover, all but one of the spongers are female, too.

At first sight, that suggests the explanation for sponging could be either cultural transmission within a clan, or genetic transmission of a recent tool-use-inducing mutation.

But the detailed statistical analysis of the genetics of the spongers that Dr Krützen carried out shows that a mutated gene could not explain the pattern of sponging individuals actually observed.

The researchers are therefore reasonably sure that what they are seeing is cultural transmission from mother to child.

Why sponging should be so sex-specific is, however, still a mystery.

Maybe female dolphins are smarter than males—or, at least, pay more attention to what their mothers tell them.



Or maybe they are just more sensitive to sticking their noses into the seabed.