Olivia Judson: What’s In Your Guts?

Dr. Olivia Judson

IT is once again our delight, dear reader, to post about a column by the splendidly-evolved Olivia Judson — an evolutionary biologist and a research fellow in biology at Imperial College London. This article, part of Dr. Judson’s series in the New York Times, is titled: Microbes ‘R’ Us. Here are some excerpts, with bold added by us:

The typical human is home to a vast array of microbes. If you were to count them, you’d find that microbial cells outnumber your own by a factor of 10. On a cell-by-cell basis, then, you are only 10 percent human. For the rest, you are microbial. (Why don’t you see this when you look in the mirror? Because most of the microbes are bacteria, and bacterial cells are generally much smaller than animal cells. They may make up 90 percent of the cells, but they’re not 90 percent of your bulk.)

Yes, but in Olivia’s case, the ten percent of her that’s human seems to be just fine. Let’s read on:

Even on your skin, the diversity of bacteria is prodigious. If you were to have your hands sampled, you’d probably find that each fingertip has a distinct set of residents; your palms probably also differ markedly from each other, each home to more than 150 species, but with fewer than 20 percent of the species the same. And if you’re a woman, odds are you’ll have more species than the man next to you. Why should this be? So far, no one knows.

Your Curmudgeon hopes that, if put to the test, his bacteria will be wondrously compatible with Olivia’s. We continue:

But it’s the bacteria in the digestive tract, especially the gut, that intrigue me most. Many of these appear to be true symbionts: they have evolved to live in guts and (as far as we know) are not found elsewhere. In providing their habitat — a constant temperature, some protection from hostile lifeforms and regular influxes of food — we are as essential to them as they are to us.

Isn’t biology fun? Here’s more:

And they definitely are essential to us. Gut bacteria play crucial roles in digesting food and modulating the immune system. They make small molecules that we need in order for our enzymes to work properly. They interact with us, altering which of our genes get turned on and off in cells in the intestinal walls. Some evidence suggests that they are essential for the building of a normal heart. …

Together, your gut microbes provide you with a pool of genes far larger than that found in the human genome. Indeed, the gut “microbiome,” as it is known, is thought to contain at least 100 times more genes than the human genome. Moreover, whereas humans are extremely similar to one another at the level of the genome, the microbiome appears to differ markedly from one person to the next.

What determines these differences? Good question. …

[...]

We know that the diversity of microbial species differs between your gut and mine, and that the less related we are, the more that will be true. Family members tend to have more similar gut microbes than nonrelatives, and preliminary evidence suggests that geography matters, too. So the gut microbes of people in China are different from those of people in the United States — though whether this is due to diet, human genes or geography is entirely unknown. …

There’s much more to the article than we can copy here. Click over to the New York Times and read it. It’s by Olivia, so you know it’s good.

Copyright © 2009. The Sensuous Curmudgeon. All rights reserved.

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