Photo: Marie-Astrid Peltier
The data keeps mounting to suggest that the development of cooking played an integral part in human evolution and the development of intelligence.The new study, published in the journal Proceedings of The National Academy of Sciences, shows that the diet of ancient humans and primates imposes a tradeoff between body size and the number of brain cells the body can support.
Generally, larger animals have larger brains, but primates are different. The largest primates, like the gorilla, do not have the largest brains — humans do. Our brains are about three times larger than those of orangutans or gorillas.
Humans first developed their big brains about 2 million years ago, around the same time we developed fire and cooking, though the evidence for fire is limited until about 1 million years ago. Cooking and processing food helps our bodies get more calories from it.
The researchers, led by Suzana Herculano-Houzel of Universidade Federal do Rio de Janeiro, wondered if this difference in diet could have led humans down the path to big brains. They analysed data on body size and feeding habits from 11 primate species.
They found that our diet sets humans apart from the primate pack.
Primates that only eat uncooked food need more to get the same amounts of energy — cooking the food helps make the calories more accessible to our digestive systems. This means humans eat less and invest less time in eating and hunting, which not only helped us develop culture but let our brains think harder, the researchers suggest.
Primates that are on a raw diet can’t support both a large body and a large brain because they can’t get as much energy from their food, the researchers found. Apes to have a brain that takes up 2 per cent for its body mass the animals would have to eat for an additional 2 hours and 12 minutes a day. A gorilla already spends as much as 80 per cent of its waking day feeding.
They found that humans on a primate-like diet would have to eat for about 9 hours a day to support their brain weight. This is similar to recent estimates from another group that found that humans with a strict raw food diet would be required to feed 48 per cent of the day.
An earlier study on primate and ancient human chew times, published in Proceedings of the National Academy of Sciences in 2011, supports the new work. These researchers, led by Chris Organ, of Harvard University, found that based on tooth size and body size, ancient human species older than 2 million years would have been chewing for much longer than modern humans and Neanderthals.
Though we developed bigger brains at that time, we didn’t really start using them until 150,000 years ago — changes that have also been linked to the way our bodies use energy.
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