Survival (or extinction) of the fittest (or luckiest)

Darwin’s original theory caught the world’s imagination because it was simple and plausible. Hereditary variation was obvious, and natural selection could mimic the role of the intelligent livestock-breeder in ensuring that the best-adapted organisms survive. In later versions of the “Origin” he adopted the term “survival of the fittest”, which he personally viewed in Malthusian and, at times, even eugenic terms. There is no doubt that Darwin had in mind “progress” and “perfection”, as reflected in the beautifully adapted and diverse life-forms we see all around us. In a previous post I tried to show by analogy that the progress of science has complicated, and weakened, that simple view.

But I want to home in a little closer on natural selection itself, which in all versions of the Darwinian hypothesis still has a key role in the “final product” of life.

Selection, in Neodarwinian population genetics, is the “creative” force in evolution that prevents the latter being a merely random process. Classically mutation is the almost-unnecessary “fuel” that keeps the gene pool topped up with variation. The neutral theory and other developments have greatly increased the importance of mutation, and there are many (often controversial) revisions of the nature and randomness of those mutations. Even so, they can all be conveniently lumped under “variation”, assumed to be random with respect to fitness, with the controlling, creative, role still assigned to natural selection.

Like the nature of “significant information” in the genome (as, actually, in information theory generally), the definition of “fitness” is hard to pin down. But defined it must be if any mathematical analysis of evolution is to be performed: fitness is the flip-side of selection. In an interesting discussion by Douglas S Robertson  such a definition (universally used, I assume) is made:

This analysis will have to begin with a mathematically precise definition of the term “fitness.” Fortunately this is straightforward: We will define the fitness of an individual as the number of progeny that an individual produces, or, more precisely, the number of progeny that survive and reproduce; progeny that do not survive and reproduce make no contribution to Darwinian fitness [my italics].

It will be seen immediately that this definition completely vindicates the accusations of tautology from critics. “Fitness” is nothing more than reproductive survival, so selection is nothing more than “the environment in which there are survivors”. If survivors survive, they survive.

In certain kinds of environment, that matches Darwin’s perfector nicely. Given a suburban garden, the early bird catches the worm, and the early gene fixes in the species. But a meteorite strike destroys every individual of every species close by, and survivors further afield may simply be lucky. A pandemic may sweep a species in a month or two, leaving a few survivors that may be resistant, yet badly unfit for their normal environment.

Imagine World War 1 which, it is often said, robbed Britain of the cream of her youth. True or not, the 10% casualty rate was almost entirely indiscriminate. Courage, skill or self-interest were marginal to survival – “fitness” was entirely a product of where the Boche dropped his shells. Some kinds of environment may preclude any survivors, or at least badly skew the effects of genetics. If predators eat 99% of young, why need competitive advantage play any part at all in which genes survive?

Even so, Robertson is able to use his definition in useful calculations, and predictions that account not only for population genetics, but for sub-optimal adaptation, punctuated equilibria, paucity of fossil intermediates and even – and here’s the interesting one to me – extinction events. One example he gives of the last is the general observation (Cope’s Rule) that organisms tend to increase in size before becoming extinct. Robertson argues that size has a selective advantage up to an environmental optimum, but that even after that it still has a competitive advantage, so that size will increase further at the expense of the viability of the species, leading to extinction.

A little thought will show that such a conclusion forces us to redefine fitness as “reproductive survival, or extinction”, and natural selection is “the environment in which there are survivors, or not.” Or, more concisely, “the environment.”

To me, the obvious result of this is to dethrone selection from its creative throne, and to reopen the issue of variation, in all its glory, as the genuinely innovative (and therefore necessarily highly non-random) force of evolution. But suppose for the moment we don’t take that step. Then in order to avoid attributing life to completely undirected chance (is your probability calculator charged up?), we have to concede a genuinely creative role to the environment, and I mean in a teleological sense. For a blind watchmaker who is just as happy breaking the best ones up is not the guy to rely on for getting you there on time. 

Environments can, and arguably should in most cases, favour uniformity and simplicity, or more likely the eradication of life in short order. They don’t have to foster complexity, variety and fertility.  But this one does. Is this, maybe, an indication of cosmic fine-tuning at the micromanagement scale? Or does it add specific substance to Genesis 1.11,20 and 24?

Jon Garvey

About Jon Garvey

Training in medicine (which was my career), social psychology and theology. Interests in most things, but especially the science-faith interface. The rest of my time, though, is spent writing, playing and recording music.
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