Over the past few million years, our ancestors have invented some great stuff. Like sharp rocks and cool art. But arguably our greatest invention was fire and the cooking it made possible. When you cook food is easier to break down, helping us get more energy out of it. It's thought that these extra calories were crucial for fueling our growing brain ( although this is debated).
And that's just the tip of the iceberg. Fire could help us survive in tough environments, scare off predators, and kill off bacteria in our food. It's clear fire was a key step in our evolution. In the process, surely we got better at dealing with fire and the food we cook? Some researchers think so, and they've got the mouse models to prove it.
Feeding mice, studying humans
Many hypothesise that cooking helped our evolution along. But did our evolution also help us deal with cooking? Some researchers hypothesised that it did. That our bodies adapted to better deal with cooked food.
Unfortunately, testing this idea on humans has some ethical drawbacks. Starving people, mucking with their diet, and scooping out bits of liver for analysis is generally frowned up. Even when it's in the name of science, and not just to find something that pairs well with a nice chianti. Hiss.
So they turned to animal models. Specifically, mice, feeding 24 of them either cooked or raw food for several days. Afterwards, their livers were examined for differences in gene expression. And sure enough, the researchers found some differences; identifying 112 genes whose expression seems to be changed by a cooked diet. On its own, that isn't too interesting. It's a well-known fact that the environment influences the degree to which a gene is expressed.
What is more interesting is that those differently expressed genes are fairly conserved in most primates. However, in humans, they show signs of undergoing positive selection. This suggests that not only does cooking influence gene expression but that it's actually driven natural selection on these genes in our species. Our bodies have adapted to eat cooked food.
Ancient origin of cooking
Interestingly, these genes haven't only evolved in us. The researchers in this study also examined our close relatives, the Neanderthals and Denisovans. We have genetic data from both of them, and it shows that they also show similar signs of positive selection in these "cooking genes".
This suggests that the impact of evolution on these genes took place before our branches separated. This happened sometime between 275,000 years ago and 1 million years ago. Logically, our species must have begun routinely eating cooked food before then. However, this research was unable to pin down the development of cooking with any greater accuracy than that.
This is especially frustrating given that the first case of cooking is a big mystery. There's circumstantial evidence our ancestors were using fire close to 2 million years ago. But it isn't the most convincing, and they don't seem to have been using it to cook food as late as 1.2 million years ago. When did someone have the bright idea of dropping some meat in the fire? It's a question researchers have debated. Unfortunately, it looks like something we will have to continue debating.
Evolving efficiency
So there are all these ancient genes whose evolution seems to have been influenced by cooking. But what do they do? How exactly has cooking influenced our evolution?
You'd be forgiven for thinking that these genetic changes conferred some increased ability to deal with cooked food. In reality, the opposite seems to be the case. In all circumstances examined, eating cooked food was linked with lower levels of gene expression. When the mice were fed cooked meat, genes linked with the immune system. And when they were fed cooked plants, genes linked with digesting carbohydrates were toned down.
In other words, the mice who ate cooked food didn't have to work as hard to deal with it. They seemed to have encountered fewer pathogens in the meat, so their immune system could take a break. And it was easier for them to digest plants, so they didn't have to work so hard to deal with that either. As a result, the genes linked with these systems were toned down; undoubtedly saving some energy and effort in the process.
The secret to cooked food seems to be that it's just more efficient. It's an answer that's not too glamorous, but when it comes to evolution, it's especially important. That conserved energy could be what you need to get through the winter, or raise another child. Evolution works in those small percentages.
Reference
Carmody, R.N., Dannemann, M., Briggs, A.W., Nickel, B., Groopman, E.E., Wrangham, R.W. and Kelso, J., 2016. Genetic evidence of human adaptation to a cooked diet. Genome biology and evolution, 8(4), pp.1091-1103.
