Evolution: Humans have Strong Stomach Acidity like Scavengers

There was a reason that animals evolved high stomach acidity. Researchers have now found that high levels of acidity weren't developed to break down food, but rather to ward against food poisoning.

"We started this project because we wanted to better understand the relationship between stomach acidity, diet and the microbes that live in the guts of birds and mammals," said DeAnna Beasley, one of the researchers, in a news release. "Our idea was that this could offer some context for looking at the role of the human stomach in influencing gut microbes and what that may mean for human health."

In this latest study, the researchers examined all of the existing literature on stomach acidity in birds and mammals. They found data on 68 species, and then collected more data on the natural feeding habits of each species. They then ran an analysis to see how feeding behavior was related to stomach acidity.

It turns out that scavengers, or species that eat food at high risk of microbial contamination, have more acidic stomachs. It's this acidity that allows the stomach to act as a filter, controlling which microbes can pass through the stomach to the gut.

"The finding confirms our hypothesis, but you have to get that confirmation before moving forward," said Beasley. "The next step will be for scientists to examine the microbial ecosystems in the guts of these animals to see how these ecosystems have evolved. Do animals with high stomach acidity have smaller or less diverse populations of gut microbes? Or do they simply host microbes that can survive in acidic environments?"

The researchers also found that human stomachs have high acidity levels associated with scavengers. This, in particular, may show that medical treatments can significantly alter the acidity in a human stomach.

The findings are published in the journal PLOS One.

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