What with all the general business and the ample supply of recent blog fodder, I seem to have gotten away from my Blogging Dawkins project. That state of affairs ends now.
In Chapter Two Dawkins laid out the case that artificial selection can and has caused enormous changes in the physical features of organisms in a relatively short amount of time. In terms of the broader case for evolution, this can be viewed as a plausibility argument. If random variations sifted through selection can craft both chihuahuas and Great Danes from a common wolf-like ancestor in a relatively short amount of time, a lot of humility is in order when asserting what can and can not happen over the course of geological time.
In Chapter Three Dawkins turns from artificial selection to natural selection. Can nature play the role of the human breeder? What, in nature, takes the place of the human eye in making selections?
Dawkins serves a number of biological curiosities to show that nature can serve as a selective agent. Based on these examples he describes the following four-step progression:
- Humans deliberately choose attractive roses, sunflowers etc. for breeding, thereby preserving the genes that produce the attractive features. This is called artificial selection, it’s something humans have known about since long before Darwin, and everybody understands that it is powerful enough to turn wolves into chihuahuas and to stretch maize cobs from inches to ffet.
- Peahens (we don’t know whether consciously or deliberately, but let’s guess not) choose attractive peacocks for breeding, again thereby preserving attractive genes. This is called sexual selection, and Darwin discovered it, or at least clearly recognized it and named it
- Small prey fish (definitely not deliberately) choose attractive angler fish for survivial, by feeding the most attractive ones with their own bodies, thereby inadvertently choosing them for breeding and passing on, and therefore preserving, the genes that produce the attractive features. This is called — yes, we’ve finally got there — natural selection, and it was Darwin’s greatest discovery.
- Without any kind of choosing agent, those individuals that are `chosen’ by the fact that they happen to possess superior equipment to survive are the most likely to reproduce, and therefore to pass on the genes for possessing superior equipment. Therefore every gene pool, in every species, tends to become filled with genes for making superior equipment for survival and reproduction.
Near the end of Chapter Three Dawkins writes:
Bear in mind this order of evolutionary change [to produce a peke and a pye-dog from a common ancestor] , and then extrapolate backwards twenty thousand times as far into the past. It becomes rather easy to accept that evolution could accomplish the amount of change that it took to transform a fish into human.
Creationists have a standard answer to this sort of thing. The differences between chihuahuas and Great Danes are, indeed, impressive, but both are still dogs. This is microevolution, and does not involve one sort of life changing into a different sort of life. While there can be extensive changes within a “kind,” there are fundamental barriers preventing evolution beyond this point. Turning one kind of dog into another kind of dog does not show that a fish can transform into a human.
At this stage of the case this argument has a certain plausibility. It becomes increasingly difficult to maintain, however, as you learn more about the anatomy and genetics of modern organisms, and sift through the fossil record for clues as to the sorts of creatures that existed long ago. We have impressive transitional fossils to show how certain, seemingly very difficult, transitions were accomplished. That reptilian jaw bones can transform into mammalian ear bones becomes much easier to believe when you can effectively watch them do so through a series of fossils. A study of anatomy and genetics makes it clear that modern structures are the modified descendants of precursor structures. This, I suspect, will be fodder for later chapters.
I will not say much about Chapter Four, except that it is excellent. Dawkins provides an impressively lucid explanation of radiometric dating and its role in establishing the age of the Earth. I have seen many explanations of these ideas, but still found myself enjoying Dawkins’ lucidity.
In terms of the broader case for evolution this is another “setting the stage” chapter. It addresses the age of the Earth question, but mostly it is preparing a discussion of the fossil record. It’s great stuff, but I am now just over one hundred pages into the book and the case is still in a rudimentary state. I suspect that will change in the next chapter. Stay tuned!