Listen, you have a big brain. Yes, it’s true. Your brain allows you to do many wondrous things, like reading this sentence, brushing your teeth, and memorizing the first 27 digits of pi. It wasn’t always so big, however. It slowly got bigger and smarter as humans evolved over millennia. So, how did it get that way? New research finds it may have had something to do with our ancient ancestors’ diet.

In a new study published in The Quarterly Review of Biology, Dr. Karen Hardy and her team brought together a wealth of data that argue carbohydrate consumption, particularly starch, was the cornerstone of accelerated expansion of the human brain over the past million years, and coevolved with copy number variation of salivary amylase genes — which help with the digestion of starches — and controlled fire used for cooking.

You’ve probably heard of the Paleo diet. This is a current trend where people try to eat like our ancient ancestors ate. This means plenty of starches and animal meat — nothing processed or artificially made. The Paleo diet was created under the impression that human physiology should be optimized for the nutritional profiles we experienced during our evolution. This means eating like a caveman, basically. Up until now, much of the focus has been on eating animal meat proteins, as well as how cooking those meats helped our brains evolve over two million years. Carbohydrates were heavily overlooked, unfortunately, so Hardy and her team set out to find just how important these starch-rich plant foods were to the evolution of our brains.

To build a case for dietary carbohydrate being essential for the evolution of our brains, Hardy and her team came up with a few observations:

  • First, they found that the human brain uses 25 percent of the body’s energy budget and up to 60 percent of blood glucose, which means that these high glucose demands wouldn’t have been met in a low-glucose diet.
  • Second, pregnancy and lactose demands put even more pressure on the body’s glucose budget, and low maternal glucose levels put undue pressure on both the mother and the baby. This meant that early humans had to eat more starches when they were pregnant, to keep both parent and child alive.
  • Third, carbohydrates were easily available to early humans, even during the nomadic days, in the form of seeds, tubers, and some fruits and nuts.
  • Fourth, the evolution of controlled fire in cooking allowed early humans to easily digest said starches, which were much harder to digest when raw.
  • Fifth, the salivary amylase gene became present sometime in the past million years and increased the amount of salivary amylase produced by early humans, thus allowing them to digest starches even better.

According to Hardy, the evolution of cooking and the salivary amylase gene went hand in hand, which led to the increased availability of pre-formed dietary glucose in the brain and fetus, which then accelerated an increase in human brain size over the next 800,000 years.

Source: Hardy K, Brand-Miller J, et al. The Importance of Dietary Carbohydrate in Human Evolution. The Quarterly Review of Biology. 2015.