Microbiome may have shaped early human populations

PUBLIC RELEASE DATE:

16-Dec-2014

Contact: David Salisbury david.salisbury@vanderbilt.edu 615-343-6803 Vanderbilt University @vanderbiltu

We humans have an exceptional age structure compared to other animals: Our children remain dependent on their parents for an unusually long period and our elderly live an extremely long time after they have stopped procreating.

Could the microscopic fellow travelers that consider the human body to be their home - collectively known as the microbiome - have played an active role in shaping and maintaining this unusual aspect of human nature?

That is the speculative proposition advanced by Martin Blaser, professor of medicine and microbiology at NYU's Langone Medical Center, and supported by mathematical models produced by Glenn Webb, professor of mathematics at Vanderbilt University. They present their argument in a paper titled, "Host demise as a beneficial function of indigenous microbiota in human hosts," published online today in mBio, the journal of the American Society for Microbiology.

Scientists have known for a long time that every species of plant and animal acts as host for a distinctive collection of microorganisms. The human microbiome consists of about 100 trillion microbial cells, outnumbering the much larger human cells by about 10 to 1. Until recently they thought that the influence these microscopic communities have on their hosts was extremely limited. But recent research has found that their influence extends well beyond aiding digestion and producing bodily odors; they also aid brain development, reproduction and defense against infection. Taken together, the new evidence has led to the hologenomic theory of evolution, which proposes that the object of Darwin's natural selection is not just the individual organism as he proposed, but the organism plus its associated microbial community.

Blaser got the idea for the impact of microbes on human age structure from his lifetime research on Helicobacter pylori, a bacterium found in the stomach of more than 50 percent of the world's population.

H. pylori co-exists peacefully in people's stomachs for most of their lives. It even has some beneficial effects. In 1996, for example, Blaser discovered that it may help regulate levels of stomach acid. However, H. pylori is also a major cause of stomach cancer, a risk that increases with age.

"I began thinking that a real symbiont is an organism that keeps you alive when you are young and kills you when you are old. That's not particularly good for you, but it's good for the species," Blaser said.

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Microbiome may have shaped early human populations