The Year in Science: Evolution

Sunday, January 08, 2006

Dolphins' Daughters Sponge for Knowledge

Scientists tracking dolphin behavior reported in June that the mothers pass tool use on to their female offspring. Researchers found that bottlenose dolphins share knowledge of how to use marine sponges for foraging, reflecting a combination of tool use and social learning.

The dolphins wear the conical tools on their nose, or rostrum, although no one knows yet how this helps them feed, says Michael Krützen, an evolutionary geneticist who coauthored the study. Krützen, a postdoctoral student at the University of New South Wales when the discovery was made, said he and his colleagues found that sponge users in Western Australia have a different diet from their pod mates. That suggests the tools let them gain access to a new food source, perhaps by protecting their rostrums as they sift the seafloor for bottom dwellers. The technique is not genetically imprinted, like nest building, and probably originated with one innovative "sponging Eve," Krützen says. "If there is a prime candidate for social learning, the dolphin is a good animal," he adds. They are skilled imitators, and female dolphins spend a long time with their mothers. So far, the researchers have seen only one male sponge wearer.

The findings come in a year that saw gorillas added to the list of tool-using animals. The primates were observed using sticks to test water depth and branches as a makeshift bridge. Finding species that both use tools and pass down learning is much rarer, though. Until this year, only chimpanzees and orangutans were known to be capable of transmitting a material culture. Dolphins are the first nonprimates to join the club.  —Elise Kleeman 

Evolution Of Human Brain Hasn't Ceased

Whether or not human thinking is evolving, the human brain certainly is. In September Bruce Lahn and his colleagues in the Committee on Genetics at the University of Chicago announced that at least two genes active in the human brain have recently evolved.

"Human evolution is not static," says Nitzan Mekel-Bobrov, a graduate student in Lahn's lab and lead author of one of the two papers published in Science. The genes studied, called Microcephalin and ASPM, help determine brain size. The genes have many different working variants, but one variant of each gene is much more common than all the others.

The researchers found that those variants first showed up about 37,000 years ago (for Microcephalin) and 5,800 years ago (for ASPM) and that their frequencies increased rapidly through natural selection. Tantalizingly, the dates coincide, respectively, with the emergence of art and symbolism in Europe and of cities and written languages in the Middle East.

No one knows whether the versions in question actually increase brain size, and the relationship between brain size and intelligence is also not clear. Nor is it known yet why these variants are more common in some places than others. If the favored versions of the genes enable people who have them to raise more children, it will be just an evolutionary blink before they're everywhere. —Jessica Ruvinsky

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