The word evolution is seeing the light of day more and more these days as the debates about evolution vs. creationism and science vs. religion, ratchet upward in public arenas like school curricula, government, churches, newspapers, magazines, and Internet forums, blogs, and websites. But what an awful lot of people are missing, is a basic understanding of just what evolution is, how it works, what it says about how life evolves from simpler lifeforms, and what it doesn't say about how life began on Earth to begin with. So, this blog entry is devoted to clarifying and simplifying evolution for the masses, for the average Joe-Schmoe, and for even for some “experts” that still get things screwed up when they talk about evolution.
First, what exactly is evolution?
Well, it's a theory of how life generally developed on Earth through the process of natural selection from simpler lifeforms, like single-celled organisms, to more complex lifeforms like trees, fish, and humans. But STOP RIGHT THERE! It's just a theory, right? Well, it's a theory alright, but NOT JUST a theory, not in the sense that many opponents of evolutionary theory use when they pit evolutionary theory against creationist theory.
Evolution is a scientific theory. It's not just a hypothesis, a proposed explanation, or even an educated guess. A scientific theory doesn't become a theory until a hypothesis or proposed explanation or an educated guess has garnered enough evidence to support it that it becomes a generally accepted fact. The theory of evolution is as much a fact as a plethora of other scientific facts like the fact that photosynthesis is the process by which green plants convert sunlight into energy. And like all scientific theories, evolution can be invalidated by a single instance that contradicts it. So far, no such instances have been found. Creationism, on the other hand, is not a scientific theory. It is not supported by the facts. In fact, it is contradicted by the facts on soooo many levels! I personally wouldn't even validate it as even a rational hypothesis.
Now, it's important to realize that there are two aspects to the theory of evolution that need to be clarified.
The first aspect of the theory, and the most important one, is the Principle of the theory - that evolution through natural selection has happened, is currently happening, and will continue to happen. It includes the principle that mutations in organisms can result in either advantages or disadvantages with respect to its chances of survival and its subsequent ability to reproduce and thus pass on the mutation to subsequent generations of the organism. Thus, an organism that has an advantageous mutation will be more likely to survive and reproduce than an organism that has a disadvantageous mutation or no mutation at all – that's basically the process of natural selection which is the basis of the theory of evolution. For example, a rabbit that has only three legs (an obvious disadvantage) due to a mutation will be less likely to survive and reproduce than a rabbit that not only has all four legs, but also has longer and stronger legs (an advantage allowing it to more easily escape predators) due to a mutation.
The second aspect of the theory of evolution involves the actual details of the specific processes, functions, and workings of the main theory. In short, we know for a fact that evolution has happened and continues to happen – that organisms “evolved” from simple lifeforms to more complex lifeforms over many millions of years. But scientists still investigate (through experiment and observation) and debate and refine the actual details of the general process/principle. For example, it is generally accepted that humans evolved from some common ancestor of humans and apes, but the exact details concerning how many years it took, what all the intermediate creatures looked like, how many mutations it took, etc., are still waiting to be filled in and verified.
So, yeah, we don't know all the details yet, but that doesn't mean that evolution didn't happen or that it doesn't continue to happen!
Now we come to explanations and characterizations of evolution that are just plain misleading and desperately need clarification. My overlying frustration with the following issue is inspired by the fact that I've seen waaaay too many scientists themselves explain, or otherwise comment about, evolution in grossly erroneous ways. I'm sure that these same scientists, or most of them anyway, actually understand evolution correctly, but simply aren't careful enough about communicating it correctly.
Here's what I mean. I can't tell you how many times I've heard or read something by a scientist to the effect of: this critter evolved a such-and-such characteristic in order to take advantage of such-and-such resources. To illustrate, here's a specific example of this error:
Certain birds developed/evolved bigger, thicker, stronger beaks in order to be able to crack and eat the bigger, harder nuts available to them as the supply of smaller, more easily cracked nuts became more scarce. They were thus able to take advantage of a food supply that wasn't available to birds with smaller, weaker beaks – so they survived and reproduced better than the other birds.This is a very common way to explain things, but it is sooooo wrong! Organisms do NOT evolve traits or characteristics in order to have advantages!! Instead, what happens is that an organism has a random mutation – there is no purpose to the mutation, it just happens without any foresight whatsoever of the possible advantages or disadvantages. (More about what causes mutations later.) Then, if that mutation happens to be advantageous one, it is more likely to be passed on to the offspring of that organism. So, here's a corrected version of the erroneous example above (with an additional couple of sentences for completeness of the idea):
A certain single/individual bird happened to have a mutation that resulted in having a bigger, thicker, stronger beak. It also happened that competition for the nuts that these type of birds could eat was getting tougher and tougher since the supply of nuts they could eat was dwindling. The bird with the bigger, thicker, stronger beak found that it could crack and eat the bigger, thicker, harder-to-crack nuts that the other birds could not. Thus it was able to survive and reproduce better than the others. So it passed along that genetic mutation to its offspring. Those offspring were, in turn, able to compete for food better and reproduce better than others. And, after a time, these birds with the bigger beaks became a new species, while the other birds became extinct.Please note that in the situation above, and in other real situations, there may happen to be No random mutations at all (or, at least no advantageous mutations), and the birds may have become extinct without evolving at all.
Finally, what causes mutations to begin with?
There are several possibilities, and not all of them are completely understood. But rest assured that mutations DO Happen, regardless of whether we understand them or not! Note though, that the vast majority of mutations are distinctly disadvantageous. Heh, if they were mostly advantageous, then evolution would happen a whole heck of a lot quicker.
Another cause of mutations may be the cosmic rays that bombard the Earth constantly. And sometimes, for whatever reason, the Earth gets hit with higher than normal amounts of cosmic radiation which may cause some mutations. Man-made radiation in excessive amounts, like the nasty stuff from a nuclear blast, is well known to cause mutations. There may be other causes of mutations, but you get the idea, right? It's all in the DNA.
What Evolution doesn't say!
Perhaps the biggest mistake that people make about evolution is thinking that the theory of evolution incorporates how life came from non-life. In reality, evolution says absolutely Nothing about how life got started on Earth to begin with. Evolution only applies to living things - the theory only kicks in once life has started, not before! As to how life actually came from non-life, well,... that's another story - perhaps even another blog entry. :-)
And that about wraps it up for this blog entry. I certainly hope that if I've erred in any of my explanations here, someone will graciously point them out to me so that I can correct them – I'd hate to perpetuate misinformation about evolution,... not after I've gone to such trouble of professing to correct some myself!