For a portion of my youth, my Attenborough-inspired self wanted to be a palaeontologist. But I outgrew dinosaurs around the same time as high school started, so physics drew me in. But again that was not to be, as learning to program in my later youth and an unhealthy fascination with video games pushed me towards becoming a programmer. Now, armed with a Computer Science degree, I've come full circle and wanted to learn all I can about nature.
Why do I bring this up? Like all posts on here, anything I write is an extension of myself. This is Kelosophy, my philosophy, my understanding of the universe being placed on the information superhighway. So when I write about why I'm such a staunch defender of evolution. And there are two main reasons I do defend evolution. Firstly evolution is the focal point of the religious assault on science, and secondly that science works so it is worth defending.
The embodiment of naturalism
As far reaching as evolutionary theory is, it is also limited to digitally-replicating bioorganisms. So while it can explain the diversity of life, it doesn't explain the origin of life or anything outside of the domain of biology. In 2005 I first started using the internet for social purposes, and I found that it wasn't enough just to be an atheist, I had to be able to explain: life, the universe and everything, otherwise God did it. And the focal point of these attacks? Evolution.
Creationist websites are filled with "gotcha" points, pseudoscientific claims about nature that are meant to undermine naturalism. But naturalism meant evolution, as it is so often used. In effect, I was forced to learn about evolution beyond what is taught in schools because at each point the attacks on evolution were used in an attempt to undermine my atheism.
I'm not saying I learned in order to fulfil my atheist world-view, I had a lot better background in physics and especially astronomy so I knew that the claims were false, and there were many claims I knew were biologically wrong. But that's the thing with "gotcha" attacks, if I didn't have an answer for a particular creationist assertion then it must have meant that evolution is wrong, God made us from clay some 6000 years ago and I'm completely immoral, leading a meaningless life and going to hell.
Evolution is strongly defended because evolution is constantly under assault, and this feeds a divide between science and religion. I used to think that science and religion were compatible, that evolution doesn't kill God and that ultimately science and religion are reconcilable if one is that way inclined. But this exposure has shown me otherwise, it's hard to keep saying "science and religion are compatible" while the attacks on science come so strongly from those religiously motivated.
An idea worth defending
If the evidence tomorrow were to show comprehensively that evolution did not occur, then I would abandon the theory. I support it now because it is the best explanation for life on earth in all its diversity, and backed by 150 years of empirical evidence. It has survived millions of papers, millions of different evidences, completely new fields of study and lines of evidence, made successful predictions about what to see in the fossil record and genetic code. Despite the constant attacks on evolution, it has survived.
To throw out evolution would be to throw out what is really important: the scientific method. Science works, and it is worth defending as a process. The methodology of science itself is what is important. Theories are tentative and always subject to the evidence. There's no evolutionary dogma, what we understand about evolution now is not as Darwin understood or wrote about it, but where the evidence points to today.
Evolution is just one theory of many, but evolution is seldom ever attacked on it alone. It's not about the mechanisms by which life diversified, but the general picture painted by science itself; one of an old earth, an even older universe and the gradual emergence of life on scales not easily comprehended by the human mind. Even if evolution as we understood it turned out to be false, it doesn't change cosmology / astrophysics / nuclear physics / geology / palaeontology / genetics or any other discipline that exists external to the truth of evolution.
The scientific process is worth defending, as so eloquently put by Ken Miller in Only A Theory. Science works, the process shows validity not only in consistency but application. Theories can predict future results to a staggering degree of accuracy, Quantum Electrodynamics is so accurate that it's like measuring the distance from one side of the United States to the other to the width of a single human hair.
The Church Of Darwin
Even if evolution were defended for nothing more than for its own sake, it wouldn't impede on the validity of the theory. Just as whether one defends the claim of Jesus' divinity because they are Christian, the truth of the matter is external to belief in it. So even if everyone who defends evolution is doing so out of faith, there's still the underlying claims of the scientific theory worth scrutinising.
I defend evolution because I defend science; it is fundamental to our society and the only tool we currently have that can adequately measure and comprehend the natural world. Evolution is the front that most anti-science theists use to attack the scientific endeavour as a whole.