Tuesday, October 11, 2011

Human personal ecology

kw: book reviews, nonfiction, biology, physiology, parasites, predators, symbiosis

Let's see, to be optimally healthy we need worms in our guts, germs on our skin (and inside also), and a better variety of foods to eat. In addition, our abilities including 3-color vision and startle reflexes, and our adrenaline flight-or-fight system, were honed by millions of years of being chased and eaten by predators large and small, and bitten by snakes.

The worm thing gets me. As Rob Dunn writes in The Wild Life of Our Bodies: Predators, Parasites, and Partners That Shape Who We Are Today, ingesting a dose of whipworm eggs, or contracting hookworm, three or four times yearly, can eliminate many "allergic" and "autoimmune" diseases such as Crohn's Disease. Humans and our ancestral primates, prior to the Twentieth Century, were universally infested with worms. Such diseases were unknown. In much of the world, most people are still full of parasitic worms, and don't get Crohn's Disease or a host of similar afflictions.

It seems to work like this: millions of years of byplay between worms and our immune system have resulted in a sort of draw. The worms trigger immune responses, but reply with "peacekeeper" molecules that calm down the immune response, thus allowing them to live in our bodies. The immune system is now used to having these peacekeeper molecules around, and overreacts when they are not, leading to allergic syndromes. I suppose if I had some really debilitating disease like Crohn's, I'd be willing to drink a worm cocktail, but the thought gives me the willies.

Then there are the germs. We are getting used to probiotics, which are germ cocktails, and yogurt with "active cultures", so we are just getting our feet wet, learning to manage our internal ecology. A chapter in the book addresses the appendix, which turns out to be a functioning organ. Millions of people have it removed every year, and seem to do well. But if you ever get Cholera, your appendix might save your life.

Cholera flushes nearly all the bacteria out of your intestines. If you can drink enough clean water while it is doing so, you'll live and come out the other side without the bacteria that produce about half the vitamins you need to survive. How will you repopulate your gut? Enter the appendix. It is filled with lymph tissue and a thick biofilm of essential symbiotic bacteria. After a bout of cholera or any other kind of heavy diarrhea, these stored bacteria repopulate the bowels and restore your internal ecology.

There are chapters about our fears and the predators that shaped them, and our color vision with its peculiar ability to detect a snake, and make you jump back, before your conscious mind notices it. The author asked his colleagues for stories about people they might know who'd been bitten by a venomous snake. To his surprise, about half of those colleagues had stories of their own. Among practicing biologists, with their worldwide travels (and tendency to pick up anything interesting), snakebite is a frequent occurrence! The reaction we have to snakes was determined when our ancestors were the size of housecats, or smaller. It takes learning to perceive a serpent as attractive.

And there is a long section about agriculture, with quite a different take on it than you'll find in most textbooks of ancient history. Rather than some triumph of ingenuity, agricultural practices, which arose many, many times and places (not just in Mesopotamia), were responses to food crises such as drought, famine or the exhausting of game reserves in an area. One group managed to subsist by drinking the milk of the Aurochs, the proto-cow; or, at least those who could tolerate the lactose in the milk survived and subsisted thereby. Others took advantage of one or another cereal grain and learned, from scratch, how to make some kind of bread, to replace whatever "gather" crop(s) had failed. Others sought out new root crops.

Imagine you live by fruits and a cold year comes along and freezes off the fruit before they are edible. You can roughly winnow barley by hand and eat it as is (I've done so). If you are an inefficient eater, and most are, some grains will scatter further from the stand of barley you found. The next year, the extra barley growing may not matter, but if several spring freezes in a row clobber the fruiting bushes, your little band of gatherers is likely to find barley is more reliable, and settle down to cultivate it. In addition to the "big four" (maize, wheat, rice and soy), there are dozens of sustenance crops worldwide, and each was probably first cultivated to stave off a food crisis. The foods that feed us well, and those that don't, will depend on which group out of several dozen or maybe several hundred, from which we are descended.

There is much more to the book. It is a fascinating read. Some of the things that might make our lives better may repel you, as the worms did me. But there is much to learn here. The kind of future we live in could well depend on those species that we welcome back into our lives.

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