"Evolution is only a theory" is a popular phrase with the "intelligent design" and creationism crowd. Far brighter and more articulate minds than mine have taken up pen and ink (or keyboard) to expose the glaring ignorance, both semantic and scientific, that underlie this motto. Evolution is, of course, a theory, but a theory is more than just an educated guess, as the Discovery Institute and their cronies would like us to believe, but a scientific fact, and it has been so since this date 150 years ago, when Charles Darwin and Alfred Russel Wallace jointly presented their theory of natural selection to the Linnaean Society of London. People often credit Darwin and Wallace with coming up with the concept of evolution out of the blue, but this is not the case; what they did accomplish was to take a somewhat amorphous idea and bring it solidly into the realm of science. In fact, prior to 1858, the creationists might have had a point: evolution was not a theory, but an as-yet unproven hypothesis. It has been suggested by some that the earliest glimmerings of the idea occurred to Linnaeus himself who, after a life of categorizing organisms, may have realized that some natural force was responsible for the nested patterns he observed. This is all conjecture, but, whatever its beginnings, the concept had, well, evolved into nearly its present form by the early 19th Century. The most famous proto-evolutionist was Jean-Baptiste Lamarck, who looked a the same patterns and correctly identified them as evidence of biological change over time. Lamarck's only major failing, and the reason he is often scoffed at by scholars today, is that he was unable to establish the mechanism underlying evolution. Darwin and Wallace, then, were not starting from scratch, but this in no way diminishes their accomplishment. It is one thing to come up with a hypothesis, quite another to move that hypothesis into the realm of theory (which is to say, again, fact). To do so requires a mechanism (in this case natural selection) and mountains of supporting evidence. Darwin, of course, collected much of his evidence on his voyage around the world in the Beagle, and then spent the next several years studying organisms closer to home, most notably pigeons and barnacles. Wallace spent many years in the jungles of Malaysia and the Amazon, often low on both money and luck (his entire Amazonian collection was lost at sea on the return to England). Both men independently came to realize that variation and differential survival were the driving force behind the diversity of life on Earth. Darwin was the first to recognize this fact, but held off on publishing it because he realized the ramifications it would have. When he realized that his younger colleague had come to the same conclusions, he was finally spurred into publishing, and on July 1, 1858, the two men presented natural selection to the world by way of the Linnaean Society (some have suggested that this apparent act of camaraderie masks the fact that Darwin's behavior upon learning he was about to be scooped was less than honorable; the historical record is murky upon this point).
The social shock waves were soon to hit, just as Darwin predicted. It is a testament to the soundness of natural selection, though, that its main detractors were social entities (the most vociferous of these being the Church of England) rather than scientists. The evidence compiled over the years by Darwin and Wallace was so substantial and well-presented that the scientific community flocked to it remarkably rapidly (a few well-known and outspoken opponents such as Richard Owen notwithstanding). Any scientific critique of the theory was ultimately shown to be flawed, and several well-timed fossil discoveries (Archaeopteryx and Java Man chief among them) helped cement natural selection as fact beyond any reasonable doubt. Social criticism continued, and is still very much in force today, but even the most vehement creationists must admit that the theory of Darwin and Wallace is a milestone in world history. July 1st has the misfortune of falling within a week of the anniversary of another epochal date and for that reason (among others) it is often overlooked. However, as this year marks the sesquicentennial of what may be thought of as science's watershed moment, I encourage everyone out there to take just a moment to give a tip of the hat (literally or figuratively) to Charles Darwin, Alfred Russell Wallace, and their theory of natural selection - still standing tall and proud after 150 years!