Evolution in a paragraph

I have long believed evolution to be inevitable – that is, given a few starting assumptions whcih virtually no one can ligitimately question, evolution, at least when defined broadly, will follow. Should this claim seem a little extravagant, I ask only that you bear with me for a single paragraph (or three if you want the implications spelled out a little). Though the following does contain simplifications, and though there are objections that can be raised, I do think there is something worthwhile in this approach. I'll publish a slightly more technical version later.

The only observation you need to insert into life’s equation is that, due to the environment they find themselves in, genes vary in their likelihood of replication. Since these days genes usually make bodies, the statement can usually be transcribed as that “bodies vary in their likelihood of producing offspring”. This is how Darwin originally conceived his theory, and the switch can usually (though not always) be effected without a significant loss of accuracy. Suddenly the phrase becomes so obvious as to be banal – all you really need accept is that a sharp-eyed hawk would probably have more offspring a blind, maimed and sterile one. And from here, the rest of the evolutionary process can best be described as… well, a mathematical necessity. Obviously, in an environment that rewards organisms that can see, have functional body parts and can reproduce, the next generation will be full of the first type of hawk. Or, to generalise: in a pool of organisms with a variable likelihood of reproducing in a particular environment, the next generation will obviously be disproportionately filled with the offspring of those that are better adapted to reproduce there. Of course, since the likelihood is statistical and not actual, a few of those that ‘should’ have reproduced will not, whilst some many of those that ‘should not’ have reproduced will do so. But the longer the sifting process goes on, the higher the odds of something well-adapted to the environment continually making it through. A passing leaf may accidentally blow through the first one, but stack enough hoops consecutively, and the only thing that can pass through to the other side is something that really can jump through hoops. In other words, come back and look in a few hundred generations’ time, and you’ll find a species remarkably well adapted to living there – which is to say, evolution has occurred.

What we’ve just shown is that the ancestors of a pool of organisms automatically tend to become better adapted to a particular environment over time. So what if the environment changes? Say, for example, the climate gradually became warmer, over five hundred thousand years. Surely it is really not hard to see that the distant ancestors of organisms living in a warming climate will not be the same as their cold-adapted predecessors? Nature might try, but her attempts would most probably end in failure. On the other hand, those that were randomly just a little better at handling the slightly hotter climate would likely survive, thus disproportionately filling the next generation. And over generations and generations and generations of increasingly warm conditions, surely the final result could be exceptionally different from the starting organism?

On this model, explaining speciation (or at least some forms) becomes a doddle. It is the same argument, except that the original group is divided into two separate groups, with differing environments. In other words, all speciation requires is the isolation (by any means imaginable) of part of the original group from the rest and that at least one of the two groups encounters a different environment. Correctly regarding each group as a separate population, the exact same argument that we have just used shows that the two groups will diverge genetically and physically. And when this process has gone on for long enough, the initial barrier (e.g. a mountain range) would become superfluous, for two groups that are separate enough cannot viably interbreed. (A man can’t – viably – mate with a crow, though we share a common ancestor.) Once this happens, you have two separate species.

Richard Dawkins, probably the finest thinker on evolution alive today, once stated that you have to be either stupid or ignorant not to believe in evolution. I have to concede that, in my more irritable moments, I agree.