How early humans evolved to eat starch, why that matters

In the 1960s, scientists discovered that some people produced extra amylase in their saliva. But it has only been in the past few years that researchers have been able to zero down on the amylase genes.

Potato domestication coincided with production of more amylase. (Express Photo)

As soon as starch — whether it be in the form of boiled rice, french fries, or momos — enters the human mouth, an enzyme in the saliva starts breaking it down. This enzyme, known as amylase, was critical for human evolution, helping the species adapt to a changing food supply.

Two new studies, one published last week in the journal Science and the other published last month in Nature, have revealed that our ancestors began carrying more amylase genes in two major waves. The first one occurred several hundred thousand years ago, possibly in response to the invention of fire, and the second one came after the agricultural revolution, only 12,000 years ago.

Why starch is a useful enzyme

In the 1960s, scientists discovered that some people produced extra amylase in their saliva. But it has only been in the past few years that researchers have been able to zero down on the amylase genes.

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Both the studies cataloged a wide range of amylase copies in people’s DNA. Some had a single amylase gene on each copy of chromosome 1, whereas most people had many more — in some cases, as many as 11 copies. These numbers were in stark contrast to even the closest extant species to humans. Chimpanzees, for instance, also make amylase in their saliva, but they carry only a single gene for the enzyme.

History in our mouths

The two studies looked at fossil evidence for when (and how) humans’ early ancestors gained more amylase genes.

Their findings indicated that natural selection might have started favouring human ancestors with more amylase genes roughly around the time humans began to create and control fire, hundreds of thousands of years ago. This is because prior to the advent of cooking, humans likely did not consume starch-rich plants, which would have been tough to chew and digest (consider eating a raw potato).

That said, the studies found no evidence that hunter-gatherers gained any evolutionary advantage from having extra amylase genes. This changed drastically about 12,000 years ago. It was then, at the end of the last ice age, that a number of societies began domesticating crops, including starch-rich foods like wheat, barley and potatoes.

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The studies revealed that DNA containing extra amylase genes became more common over the past 12,000 years as people with more amylase genes were more likely to survive and reproduce with the kind of nutrition that was now available. The study published in Science also found that extra copies of amylase rose rapidly in the past few thousand years in Peru, where potatoes were domesticated over 5,000 years ago.

Speculation for future

Omer Gokcumen, a geneticist at the University at Buffalo who led the Science study, speculated that people today who have fewer amylase genes may be more vulnerable to diseases like diabetes, that are fueled by a starch-heavy modern diet.

He said that more amylase might prompt people to make more insulin, which would in turn make them absorb more sugar from starch. Down the line, the findings could point to potential amylase-based treatments for these diseases.

ENS with inputs from the NYT