Future Humans by Scott Solomon

Author:Scott Solomon
Language: eng
Format: epub
Publisher: Yale University Press (Ignition)
Published: 2016-11-15T00:00:00+00:00

5. Small Partners

Although we might not like to think about it, our bodies are teeming with alien life. Our skin is literally covered with bacteria and fungi and crawling with the tiny legs of microscopic animals. Look inside the average person’s mouth, as any dentist can tell you, and you will find an entire ecosystem dominated by bacteria. Further down the digestive tract, the stomach—and to an even greater extent the intestine—are veritable microbial jungles.

Until recently, most of these microscopic critters were thought to fall into one of only two categories: either they were nasty germs that should be killed lest they cause disease or harmless passengers simply along for a ride. The idea that there might be a third category, that some of them might be doing something helpful, seemed like medical blasphemy. An idea that until recently seemed even more outrageous—that some of these microorganisms might be not only helpful but an integral part of how our bodies function owing to millions of years of evolving together with us—is only just beginning to emerge.1 If microbes influenced human evolution in the past, then our continuing evolution may depend in part on what becomes of our small partners.

Ironically, with as much as we know about human anatomy and health, we know far more about how other animals interact with microorganisms than we do about our own intimate associations with microbes. Many animal species engage in symbioses with microorganisms, without which they could not survive. One example is the leafcutter ants of Central and South America, which depend on fungi as their main source of food.2 They grow enormous gardens of the spongy, gray fungus deep inside their massive underground nests, where millions of worker ants are constantly toiling to bring fresh leaves for their fungal crop. In this case, the fungi have become completely dependent on their ant servants—unlike closely related fungal species that can live on their own, the fungi grown by leafcutter ants are never found outside an ant nest. They have, in other words, become domesticated.

The lab where I undertook my doctoral work at the University of Texas at Austin, led by Ulrich Mueller, was at the forefront of research on the interactions between ants and microbes. Naturalists and scientists had known for more than one hundred years that leafcutter ants were not eating the leaves themselves but effectively using the fungi as a kind of external digestive system because the ants cannot break down plant matter on their own. Aside from the fungus garden, the rest of the nest was thought to be a relatively sterile environment. The ants are fastidious in their cleanliness, moving unwanted debris, bits of dead fungus, and dead ants to waste chambers kept far away from their precious crops. So it came as a surprise when a Canadian microbiologist, Cameron Currie, who joined Mueller’s lab as a postdoctoral researcher around the same time I joined as a graduate student, discovered that another species of fungus was commonly associated with the nests of fungus-growing ants.

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