New York, Nov 1 (IANS): When it comes to brainpower, humans may not be as exceptional as we like to think as researchers have found that some animals including the world's smallest monkeys devote a large proportion of their body energy to the brain, just as we do.

Even the ring-tailed lemur and the tiny quarter-pound pygmy marmoset, the world's smallest monkey, devote as much of their body energy to their brains as humans do, said the study published in the Journal of Human Evolution.

"We don't have a uniquely expensive brain," said study author Doug Boyer, Assistant Professor at Duke University in Durham, North Carolina, US.

"This challenges a major dogma in human evolution studies," Boyer added.

The study compared the relative brain costs of 22 species.

The results suggest that the ability to grow a relatively more expensive brain evolved not at the dawn of humans, but millions of years before, when our primate ancestors and their close relatives split from the branch of the mammal family tree that includes rodents and rabbits, said Arianna Harrington from Duke University.

Previous studies calculated the amount of energy needed to fuel a brain based on neuron counts.

But because the current study's method for estimating energy use relies on measurements of bone, rather than soft tissue such as neurons, it is now possible to estimate brain energy demand from the fossilised remains of animals that are extinct too, including early human ancestors, according to the researchers.

"All you would need to take the measurements is an intact skull and some of the neck vertebrae," Harrington said.