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As the human species has evolved over millions of years, there have been some steady companions - microbes. New research published in the journal Science looks at how those microbes have been passed down from one generation to the next. NPR health correspondent Rob Stein has the details.
ROB STEIN, BYLINE: Millions of microbes live in our bodies and do all sorts of things to help us live long, healthy lives. But Andrew Moeller of the University of California, Berkeley, had a question. Where did we get our microbes?
ANDREW MOELLER: Not just the question of where each individual gets their bacteria from during their life, but where did the species of bacteria that populate humans come from originally?
STEIN: So Moeller and his colleagues deciphered the evolution of our microbes by analyzing the DNA and bacteria living in the guts of humans and our closest relatives, like...
(SOUNDBITE OF CHIMPANZEE CHATTER)
STEIN: ...Chimps...
(SOUNDBITE OF BONOBO CHATTER)
STEIN: ...And bonobos...
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STEIN: ...And gorillas.
MOELLER: We found that the evolutionary relationships among human chimpanzee and gorilla gut bacteria mirror the evolutionary relationships among humans, chimpanzees and gorillas.
STEIN: When our evolution took a different path from gorillas 15 million years ago, the bacteria in our guts and the guts of gorillas parted ways, too. And when we evolved into humans instead of chimps or bonobos about 5 million years ago, our microbes evolved right along with us.
MOELLER: Our bacteria seem to be evolving with us over time. They've been passed down from generation to generation over millions of years just like our genes have been. They're a part of us just like our genome is a part of us and are a part of what make us uniquely human.
MARGARET MCFALL-NGAI: That's, in my mind, pretty profound.
STEIN: Margaret McFall-Ngai is a biologist at the University of Hawaii.
MCFALL-NGAI: What's really amazing about this is it really at some level changes the idea of what we think of as a human. A human is not just the genes and cells that make up the human body that are uniquely human but also the cells that are microbial. We are an ecosystem.
MCFALL-NGAI: A complicated ecosystem of human cells and genes and microbial cells and genes that all evolved an intimate relationship together over the eons. Martin Blaser of New York University says that helps explain how our microbes got involved in so many things our bodies do, how our immune systems work, how our metabolisms are regulated.
MARTIN BLASER: It tells us that the microbes in the human body are not accidental. They're not recent, but they're really a part of our ancestry. These are strong indications that these microbes are important to us. Otherwise it's not clear that they would've stuck around for such a long time.
STEIN: But not all our microbes have stuck around. Some have gone extinct, and that may be part of the reason some diseases are skyrocketing.
BLASER: There's more and more evidence of ongoing extinctions in humans of microbes, and we and others have linked this loss to the rise of modern diseases like asthma, like obesity, like diabetes.
STEIN: So Blaser and others say we need to be way more careful how we use antibiotics and do other things to better protect the microbes we evolved with. Rob Stein, NPR News. Transcript provided by NPR, Copyright NPR.
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