( ring cognitive evolution he said. Su...)Study suggests evolutionary link between diet, brain size in orangutans

In their study, Taylor and van Schaik focused on several varieties of orangutans, an endangered primate closely related to humans.

Members of the orang species inhabiting Sumatra, called Pongo abelii, live in the island's most favored environment, where soils are best for growing the fruits they most like to eat. "They'll eat fruits as often as they can, and they'll travel farther away for them if not nearby," Taylor said.

Sumatra also appears to be less subject to periodic "El Niño" climatic fluctuations that disrupt vegetative growth on other islands in the Indonesian region, the researchers' report said.

The scientists found that the nutritionally well-off Sumatran orangutans differed most strikingly from Pongo pygmaeus morio, one of the three subspecies occupying the island of Borneo. The morio subspecies lives in the northeastern part of the island where soils are poorer, access to fruit is most iffy and the impact of El Niño events can be significant.

Those factors "converge to produce an environment for orangutans of eastern Borneo that is at times seriously resource-limited," the scientists wrote. During extensive fruit-short periods, the animals have to "resort to fallback foods with reduced energy and protein content, such as vegetation and bark," they added.

In previous studies, reported in the April 2006 issue of the Journal of Human Evolution, Taylor found evidence that orangs living in Borneo's northeast have jaws that are better able to handle tougher varieties of food than orangutans in other parts of Borneo or Sumatra.

This improved feeding efficiency, coupled with a relatively small brain, would enable such animals to adapt to their conditions by both maximi
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Source:Duke University