Long before humans began hunting large mammals for meat, a diet of fats provided the energy needed to grow larger brains, according to a new study published in Current Anthropology. .
The study claims that our ancestors acquired a taste for fat by eating bone marrow from the skeletal remains of animals eaten by other predators. The argument challenges the widely held view among anthropologists that eating meat was the critical factor driving the evolution of humans.
According to Jessica Thompson, lead author of the study and an anthropologist at Yale University, our ancestors likely began to acquire a taste for fat 4 million years ago, which explains why we continue to consume it today> . The fat deposits in the large bones of the skeletons were a huge source of calories in a scarce environment. That may have been what gave an ancient population the edge it needed to trigger human evolution .
The differences between both hypotheses are significant. The nutrients in meat and fat are different, as are the technologies needed to access them. Eating meat is traditionally combined with making sharp stone tools, while obtaining fatty bone marrow required nothing more than crushing bones with a rock, Thompson says.
The study authors propose that the craving for bone marrow may have led not only to an increase in brain size, but also to the creation of more sophisticated tools to hunt larger animals.
Co-authors on the paper include anthropologists Susana Carvalho of the University of Oxford, Curtis Marean of Arizona State University, and Zeresenay Alemseged of the University of Chicago.
The human brain consumes 20% of the body's energy at rest, twice as much as the brains of other primates, which are almost exclusively vegetarian. It is a mystery to scientists how our human ancestors were able to meet such a level of caloric and energy demand to maintain their brains and make them bigger and bigger.
The meat-centric paradigm hypothesizes that an ape population began to more actively hunt and eat small animals, which became an evolutionary stepping stone toward human large-animal hunting behavior.
The new study argues that this theory makes no sense nutritionally:wildlife meat is lean, and it actually takes more energy to metabolize lean protein than you get back em> .
In fact, eating lean meat without a good source of fat can lead to protein poisoning and acute malnutrition. Early explorers of the Arctic, who attempted to survive exclusively on rabbit meat, described this as rabbit starvation .
This protein problem, along with the energy required for an upright ape with small canines to capture and eat animals, seems to rule out meat consumption as a way to stimulate brain growth, according to Thompson.
The new hypothesis traces this evolutionary leap back to about 4 million years ago, during the Pliocene. At that time our ancestors would stalk their prey on the African grasslands. After a predator finished eating a large mammal, these upright apes appropriated the leftovers by breaking them open, uncovering the hidden marrow in the limb bones.
The hypothesis offers an explanation for how humans could have stockpiled the calories needed to fuel brain growth long before there was evidence of fire control, something that could have solved the problem of bacteria in rotting meat. The fat hypothesis would also predate most evidence of simple basic stone tool making by more than 1 million years.
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Origins of the Human Predatory Pattern:The Transition to Large-Animal Exploitation by Early Hominins, Jessica C. Thompson, Susana Carvalho, Curtis W. Marean, and Zeresenay Alemseged (Current Anthropology) / Yale News.