New York, Feb 6 (IANS): A fatty diet provided our early human ancestors with the nutrition to develop bigger brains, finds a study challenging the widely held view that eating meat was the critical factor in setting the stage for the evolution of humans.

The study by Yale University researchers argued that our early ancestors acquired a taste for fat by eating marrow scavenged from the skeletal remains of large animals that had been killed and eaten by other predators.

"Our ancestors likely began acquiring a taste for fat four million years ago, which explains why we crave it today," said lead author Jessica Thompson, anthropologist at Yale.

"The reservoirs of fat in the long bones of carcasses were a huge calorie package on a calorie-poor landscape. That could have been what gave an ancestral population the advantage it needed to set off the chain of human evolution," she added.

While focusing on fat over meat may seem like a subtle distinction, the difference is significant, Thompson said.

The nutrients of meat and fat are different, as are the means required to access them. Meat eating is traditionally paired with the manufacturing of sharp, flaked-stone tools, while obtaining fat-rich marrow only required smashing bones with a rock, Thompson noted.

The fat hypothesis also predates by more than one million years most evidences for even basic tool making of simple stone flakes.

Scientists ought to begin looking for evidence of bone-smashing behaviour in early human ancestors, Thompson said.

For the study, reported in the Current Anthropology journal, the team reviewed evidence that a craving for marrow could have fuelled not just a growing brain size, but the quest to go beyond smashing bones with rocks to make more sophisticated tools and to hunt large animals.

The new paper presents a new hypothesis, going back about four million years, to the Pliocene.

The hypothesis offers an explanation for how the human ancestor may have garnered the extra calories needed to foster a larger brain, long before there was evidence for controlled fire, which could have mitigated the problem of bacteria in rotting, scavenged meat, the researchers said.