Biology Diet and Evolution
The Quarterly Review of Biology, September 2015 issue
Authors: Karen Hardy, Jennie Brand-Miller and Others
Scientists have long recognized that the diets of our ancestors went through a profound shift with the addition of meat. The new research argues that another item added to the menu was just as important: carbohydrates, bane of today’s paleo diet enthusiasts.
In fact, the scientists propose, by incorporating cooked starches into their diet, our ancestors were able to fuel the evolution of our oversize brains.
Although previous studies have highlighted a stone tool-mediated shift from primarily plant-based to primarily meat-based diets as critical in the development of the brain and other human traits, the study argues that digestible carbohydrates too were necessary to accommodate the increased metabolic demands of a growing brain.
The researchers also acknowledge the adaptive role cooking played in improving the digestibility and palatability of key carbohydrates. The study provides evidence that cooked starch, a source of preformed glucose, greatly increased energy availability to human tissues with high glucose demands, such as the brain, red blood cells, and the developing foetus.
The study highlights the auxiliary role copy number variation in the salivary amylase genes may have played in increasing the importance of starch in human evolution following the origins of cooking.
Salivary amylases are largely ineffective on raw crystalline starch, but cooking substantially increases both their energy-yielding potential and glycemia. Although uncertainties remain regarding the antiquity of cooking and the origins of salivary amylase gene copy number variation, the study, its authors say, makes a testable prediction that these events are correlated.
“Cooking would have made wild tubers much more nutritious to humans,” study author Mark G Thomas told The New York Times. “Which is not to be sniffed at, especially if you’re a very hungry Pleistocene hunter-gatherer.”
Another clue to the importance of carbohydrates, Dr Thomas said, can be found in our DNA. Chimpanzees, our closest living relatives, have two copies of the amylase gene in their DNA. But humans have many extra copies — some people have as many as 18. More copies of the amylase gene means we make more of the enzyme and are able to derive more nutrients from starches, he said.
(ADAPTED FROM STUDY ABSTRACT, REPORT IN THE NYT)