Greatly exaggerated

I happened to find The Wilson Quarterlyat the magazine stand last week. It features an interesting blend of perspectives, and I may blog rather heavily from it in the next month or so.

The item linked above, originally published as "Are We Still Evolving? by Gabrielle Walker, in Prospect (July 2004), is retitled here, "Is evolution dead?"

I've seen this idea in print before, and I expect I'll see it again, and again.

As humans continue to advance, their evolution may be grinding to a halt. Natural selection works by picking and choosing among millions of random mutations that occur in each generation, favoring those individuals who bear traits conducive to survival and punishing those with less desirable traits. But we have molded our environments to such an extent that natural selection may have nothing left to work with, observes Walker, a British science writer. All that’s necessary to get everyone’s genes on a level playing field is for people to be able to grow up and reproduce, claims geneticist Steve Jones, of University College, London. And modern technical and cultural developments have assured precisely that. In Britain, a baby who reaches six months of age today has a nearly 100 percent chance of surviving to adulthood. Only 150 years ago, about half the babies born in London died before they reached puberty.

This is an example of what I'll call the "body count" model of evolution. It's the notion that unless creatures die, unless there's blood to redden Nature's tooth and claw, selection isn't happening, and therefore neither is evolution.

The problem with that notion is, selection still happens even when all the members of a population live beyond their reproductive years.

In a population, for example, where there is competition for mates, there will be a tremendous amount of what is called "sexual selection". A member of the population with a greater amount of a charactistic that attracts mates will be more likely to reproduce. A member with a deficit in that area will be less likely to reproduce, and therefore less likely to pass its genetic endowment to the next generation, even if that genetic endowment confers every long life and excellent health.

In human society, even if we could erase all causes of death before age 50, there would still be large differences in attractiveness. Some people will be more physically attractive than others, others will have greater material success than others, and still others will be more willing to do the work of raising kids than others.

Walker mentions cultural effects and acknowledges that they exert selective pressure even if everyone survives to reproductive age.

One reason is that—as experts on both sides of the fence agree—cultural changes can affect evolution. A past example of that is the “grandmother effect,” which explains why women don’t die off soon after their child-bearing years, as other female primates do. The speculation is that, as Earth’s climate turned colder and drier and plants grew tougher and more deeply rooted 1.8 million years ago, having Grandma around to manage the increasingly hard work of foraging while Mom tended to the brood became essential to survival.

(Again, that body-count paradigm.)

Culture enters in to the equation in a bigger way than that. Certainly, some cultural mores promote survival and prosperity better than others do. Indeed, it can be argued that many of the fundamental similarities between moral codes of different cultures exist because those cultures that had different sets of moral codes did not survive.

However, we can see some discussions about cultural selection going on today, if we look. One of the comments arising from the endless discussion over the difference between "red states" and "blue states", and especially "red vs. blue" counties, is that family sizes are larger in red areas than in blue ones. There may be any number of reasons for this difference.

Areas that are largely rural may still have large people living and working on farms so that children become additional hands to do work sooner than they do in urban areas.

Family size seems to be inversely proportional to wealth. Certainly worldwide, the higher per-capita income is, the less inclined people are to have large numbers of children. For one thing, there's more assurance that any given child will live long enough to support the parents.

But there is an idea that may account for a lot of the difference in the US: People in the red states may have larger families because they're more likely to believe in a doctrine of "be fruitful and multiply". People in the blue states, on the other hand, are more likely to believe in a doctrine of "the world is overpopulated, don't add to it."

In any event, the total fertility rate in the blue areas of the US is below replacement levels. Barring immigration, their populations will decline. (I don't know if red areas are increasing, or just declining more slowly.) This differential reproduction yields no body count – those who are selected against are simply never produced in the first place. Yet it is, and remains, evolution in action.