Some future evolution scenarios
Because of my work on recent human evolution, people ask me a lot -- I mean, an awful lot -- what our evolution will be like in the future.
This is not a silly question. Evolution is a process, and like many processes we can examine its course in the past and make some observations about whether it was jerky or smooth, fast or slow. Population and quantitative genetics let us predict what will happen in populations under given patterns of selection and drift. So it seems like we ought to be able to make some intelligent predictions about where things are going.
Yet as a system, evolution is a lot like the stock market. We can make a few sensible predictions, both over the short and long terms. If there's a crisis in the Middle East, then stocks in ethanol producers will rise. Three decades from now, the S&P 500 will be higher than it is now.
But when we reduce down to particular observations, the stochastic factors become more and more important. Technological innovations drive entirely new business models and industries, yet are hard to predict. Wars have uncertain outcomes, as do elections. Even index investors in for the long term may lose money over a decade or two -- just ask anyone who started investing in 1999. The results are, we say, more volatile.
So I often cringe when somebody asks me where we're going. There are many possible futures. Some present trends might allow one to extrapolate a bit into the future, but it's hard to see how they will interact with each other.
That would be bad enough, but there's another problem. Anybody who writes about this problem always exaggerates the wacky possibilities. Like humans diverging into Morlocks and Eloi. Or how women are going to get more beautiful. Or how we're all going to converge into a mass of uniform brown.
It almost makes me want to turn into Steve Jones. OK, well, that's not going to happen. But it's frsutrating.
A couple of months ago, Carl Zimmer told me he had been commissioned to write an essay about where human evolution is going in the future, as sort of a conclusion of the year of Darwin. My immediate reaction was, "Finally, somebody who has a chance of describing this incredibly complex problem and getting it right!"
My second reaction was, "Wow, I'm glad I'm not him."
His essay appears today in Science: "On the origin of tomorrow" (a reader points out that Zimmer has a free copy in his archive). I think he's done a good job of it. He avoids the sensational, and talks in a sensible way about the relation of recent selection to future change (maybe very little, for many of the recently selected alleles).
On the other hand, civilization has also blunted some of natural selection's power over humans, particularly in the 150 years since Darwin published On the Origin of Species. Back then, for example, some children had the misfortune to be born with defective copies of a gene for an enzyme that breaks down amino acids in the food they ate. This disorder, known as phenylketonuria, generally led to severe brain damage. Few people with severe phenylketonuria were able to pass on their genes. But today, now that scientists know what causes the disease, people with phenylketonuria can enjoy fairly normal lives simply by being careful about the foods that they eat, and they pass their genes on to their children. Other medical advances, from eyeglasses to antibiotics, may also allow some potentially detrimental genes to become more common than in the past.
Zimmer was handed a great gift in the recent report on the Framingham Heart Study, which shows rather strong changes in the composition of the population over the last few decades:
The scientists discovered that a handful of traits are indeed being favored by natural selection. Women with a genetic tendency for low cholesterol, for example, had more children on average than women with high cholesterol. A greater body weight was also linked with greater reproductive success, as was shorter height, lower blood pressure, an older age at menopause, and having one's first child at an earlier age.
These changes aren't mortality-driven; they're fertility driven. Which is pretty interesting, since many of them -- blood pressure, cholesterol -- we wouldn't classically link with fertility outcomes. But fertility selection is really the only strong factor that can operate on Westernized populations today.
He also took the opportunity to broaden the question beyond human evolutionary changes to human-induced changes in the evolution of other species. This move has two great advantages for his essay: it puts many good empirical cases into reach, and it allows him to posit strong directional selection -- making evolution plausible in the short term. These examples include both intentional (genetic engineering synthetic microbes, fisheries biology) and unintentional (alien species, effects of ocean acidification).
I think it's a nice pairing -- the uncertainty of future human changes helps to underline the uncertainty of predicting what will happen in a human-altered nature.
References:
Zimmer C. 2009. On the origin of tomorrow. Science 1334-1336. doi:10.1126/science.326.5958.1334
