tomclegg.net |
Unlikely Posted May 27, 2001 I was listening to the Echoes show the other night, and Brian and Caleb were having a little discussion about evolution and creation theories. They mentioned a few arguments against using an evolutionary theory to explain the origin of species. They made a distinction between microevolution and macroevolution. Their idea seemed to be to accept microevolution as a way for species to change, or adapt; but to reject macroevolution because it hasn't been proved that evolution can cause new species to exist. In other words, evolution can cause modifications new varieties, but not new species. Like most arguments against evolution, this only makes sense if you ignore the last 130 years of biology, starting with Charles Darwin. The point of Darwin's Origin of Species was to explain how microevolution and macroevolution are exactly the same thing. Varieties and species are both created in the same way. You can't see evolution happening, any more than you can see God. All you get is indirect evidence. And all of the available evidence suggests that species are not created suddenly. Darwin's Galapagos Island finches started out as one species, but when some of them moved to a different island and the two groups no longer had contact with each other, they evolved separately. Eventually, they became sufficiently distinct from each other that they had to be called different species, although they obviously shared a common ancestry. A similar argument to the varieties-and-species one, is that there are only so many combinations of existing species. So there is a limit to how far evolution can go. But evolution doesn't work by combining existing species. It works by selecting individuals from each new generation, all of which are different from the previous generation. Of course, they're also different from all other species, but the main thing to remember is that they're different from other individuals of the same species. Other arguments included the old standard, "look at how complicated and beautiful living things are -- this couldn't possibly have happened by accident." There are several answers to that complaint. Perhaps life is beautiful to us because we are life. To an impartial alien visiting Earth, butterflies might be no more complicated and beautiful than a piece of gravel. Or you could look at it in terms of numbers. If life has been around for a few million years, and there are millions of creatures born every day, that gives you trillions upon trillions of births. So if there was any kind of life at all a few million years ago, and each birth produced something unique which was capable of reproduction, then it would be an astounding coincidence if all those trillions of births didn't result in some kind of pattern. But the main flaw in that argument is the word "accident." Evolution doesn't happen by accident, any more than gravity and friction happen by accident. Mutation is an accident, more or less; Darwin's theory of natural selection explains how Nature turns these accidents into evolution. Part of the reason it's a good theory is that it's so simple. Some organisms will live long enough to reproduce, and some won't. There are bound to be patterns, because some of the accidents will be beneficial and some will be harmful. Some of the beneficial patterns will be inherited by the next generation, and the next, and the next; and eventually they become characteristics of the entire population rather than just one or two individuals. So evolution is not an accident. Evolution is inevitable. If heredity exists -- and it certainly does or I probably wouldn't be so skeptical -- and if all organisms reproduce sufficiently fast that some individuals must die sometimes -- which even elephants do, and they're the slowest breeding animals on Earth -- then evolution happens. So the origin of species is no longer the great mystery it once was. It's still fascinating, but now that we know how DNA causes unique mutations and passes them on to future generations, it makes a lot more sense. True, evolution hasn't been proved to work, but then again, neither have Newton's laws, or relativity, or the fact that smoking is bad for your health. It's the only reasonable explanation that's consistent with biological research, and it's served us well for well over 100 years, so you could say it's just as well proved as anything in science. --- If it happens once, then it can happen again. That's what DNA is all about. But what about the very first DNA molecule? How did that happen? Did God create the first double helix, and throw it into the ocean, knowing that in time it would reproduce and evolve into a huge variety of living things? Perhaps He started with a few "sample" species, to give the process a little head start. Or perhaps He made the ocean in such a way that a molecule of DNA would almost randomly appear. But what is DNA? Sure, it's deoxyribonucleic acid, a molecule that looks like two long spiral staircases twisted together -- but what is its special property that allows it to sustain life? There are other molecules with equally silly names, and equally improbably shapes, but they don't do reproduction and heredity. There are different kinds of DNA, like human DNA, sheep DNA, and cockroach DNA. So it's not really a molecule, so much as a type of molecule. All molecules have forces that hold them together, as if to justify the effort that went into making them. But any molecule can be broken. Usually, common molecules are common for the sole reason that they are readily made. Water molecules are readily made, because hydrogen and oxygen atoms are very common, and they often happen to come together in just the right positions so they can hold on to each other. If you lose one, you can make another. But a DNA molecule is huge, at least compared to a water molecule, and it's not as likely that all the right atoms will just happen to appear in the right positions. But DNA does have the unique ability to replicate itself, and to combine with other DNA molecules. When it combines with other DNA molecules, the new molecule has exactly the same structure, but a different combination of the four acids G A T and C. So DNA is a molecule whose purpose is to ensure that there will always be DNA. Its strategy is simple but effective. It creates more DNA molecules, but it makes each one different. If every DNA were the same, then some circumstance might arise that would cause every single one to be broken. But if every one is different, then such a circumstance becomes less and less likely. You could attribute this strategy either to DNA, or to living things in general. Either way, the miniscule probability that the first DNA molecule could accidentally spring into existence is about equal to the miniscule probability that it would ever be destroyed once it did. In other words, it's a supremely unlikely molecule, but just one is enough to provide everything you need for evolution to work. |