Starchy diets affected gene copy number.

A new paper published last week looks at diet and the evolution of the human amylase gene copy number. The paper very nicely stacks a pile of evidence that starts to tell another story in human evolution.

Let's start at the top. In humans (and many other animals), the digestion of starch starts in the mouth. The enzyme responsible for starch digestion is called amylase, and specifically, the human salivary α-amylase. Given this genetic component, can we find variation between different human populations? The answer it turns out is yes, and it's correlated with the historical consumption of starch by these different groups of people.

The paper looked at three populations of people that have historically had a diet high in starch and four populations that have historically a diet low in starch. The data they uncovered was that people from high-starch populations tended to have more copies of the amylase genes - in one case 14 copies! - than people from from low-starch populations.

The conclusion that it's definitely evolution still needs more evidence, but the story is starting off to a great start. Why is the conclusion not 100% done and dusted? For each of the populations, we need to check two things:

• Is this variation found only in the amylase gene or is this a typical feature in the populations in question? To answer that, we check variation in other genes in these people and see what's typical and compare the amylase gene variation to the typical rate. The researchers of the paper couldn't do that for all populations, but for one population, a Japanese one, they did find that the amylase variation was significantly more than the most of the rest of the genome, i.e., something is going on and it's not random.
• Which copy number is the base case? One hypothesis that we need to check is that high copy numbers of amylase is the typical state in humans and that populations lost copies when their diets shifted to lower starch content. To fix this, we need to check more people from all over the world to figure out the details.

Still, it's a great first chapter of this story. Watch this space!