Evolution: A Definition

While browsing the Essay section, I often stumble across long diatribes on the subject of evolution. Many of the authors are subscribers to the hypothesis (not theory; I'll get to that) of 'intelligent design,' a school of thought maintaining that many parts of life on Earth are too complex to have been created by mere cumulative chance. Many authors also seem to be unclear on the methods by which evolution occurs, a problem which I will seek to remedy.

First off, evolution is defined as the change, over time, of the gene pool of a population. A population is any group of organisms of the same species which have no major barriers to breeding: a group of gorillas in one forest is a population, but two groups of gorillas living on either side of an impassible gulch are two separate populations. In short, evolution happens to groups, not individuals--and it happens between generations, in the differences between adults and children and between victims and survivors, not during the lifespan of a single organism.

Sometimes people dismiss evolution as "just a theory." This is the result of a disconnect between common usage and scientific jargon. We often use the word 'theory' to describe an idea we have, not necessarily supported by any evidence. Scientists call such an idea a 'hypothesis'--an idea that could explain some aspect of the universe, but which has not been sufficiently tested. An idea that is fundamentally untestable (such as the existence of God) can never be either absolutely proven or absolutely refuted--which is the failing of the concept of 'intelligent design.' An idea may explain our observations, but if it cannot be tested, then we can make no conclusions about its veracity. A theory, in scientific terms, is a hypothesis with an extensive backing of evidence--observations, experiments, and research conducted by many different scientists over time. Evolution is one such idea--the wealth of evidence supporting evolution is one of the most thorough in all of science, simply because so many people have challenged it through the years.

Now to describe the actual processes of evolution in a little more detail. Within an isolated population of organisms, evolution is constantly occurring, by two roads: natural selection and mutation.

Evolution by Natural Selection

Natural selection, despite its name, is not a form of 'choosing.' The theory is not intended to imply the conscious decisions of some discerning power. Instead, natural selection could better be described as "Evolution by Death." Natural selection is the term for what happens when individuals interact with their environments and end up the worse for it.

If two monkeys are in a clearing at night, and the two are identical in every way except for the white pelt of Monkey A and the black pelt of Monkey B, we have a potential arena for natural selection. Look! Here comes a ravening Monkeybird! It has poor night-vision, but it certainly sees Monkey A's white coat against the dark ground. It homes in, snatches Monkey A, and eats him up! We've just witnessed natural selection in action.

Different individuals have different traits, and when the traits they have are bad for them, they snuff it. Then the surviving organisms, who, by definition, are more 'fit' because they're still around, have kids and thus pass on their successful traits. Natural selection is just a convenient label for a basic fact of life that we can watch around us on a daily basis. When you spray Raid on a bunch of ants, most of them die. But the ones that live are alive because of a special trait--some randomly-occurring feature that gives them a tolerance to Raid. And since they are the only ants left, they will breed without competition, and pass on their successful anti-Raid genes. Then, when you come back later and spray Raid again, you may find that it was not as effective this time around. Spray Raid every day, and you are exerting a strong 'force' on the ant population--which will quickly adapt.

That's natural selection. When we speak of other things, such as nature 'selecting' certain 'better' organisms, we are just applying convenient labels to this simple concept, not implying that a greater intelligence is calling the shots. It doesn't get any more complicated than the above, unfortunately for evolution's naysayers.

Evolution by Mutation

The second way in which gene pools change is through mutation. Reproduction is a complicated process, and sometimes the little proteins that do the grunt work of breeding screw up, and accidentally fumble some DNA. When mutations like this occur, they cause a change in the organism--usually a very small one. A single mutation will not usually make or break a creature's fitness, but over time--over a very long time--over a time period so long that our little minds can't even seriously comprehend it--the changes build up.

And that's what makes evolution work--accumulated change. Just as the passage of uncountable feet along a stone stairway slowly wears down even granite steps, tiny, sometimes random changes to a gene pool can, if they happen for long enough (and evolution can take millions of years--or a single day), result in major changes in evolutionary direction for a species.

Mating is one of the key facets of evolution, but it's an involved topic I'll get to later.

There's more, of course--concerning speciation, the way in which new species arise, for example. Or perhaps I could detail some of the myriad cases in which evolution has been, not proven, for nothing in science can be truly proven, but at least substantiated. I’ll leave that for the next chapter.