Chapter 2 starts by offering an unexpected reason that the theory of evolution took so long to appear. As Dawkins says—since it is such an elegant and enlightening theory, why not earlier? I fully expected him to blame entrenched religious thought about divine creation. Instead, he blames essentialism. Just as a triangle drawn in the sand is a crude representation of a perfect triangle, so all life is a crude approximation of its essential ideal.
Biology, according to Mayr, is plagued by its own version of essentialism. Biological essentialism treats tapirs and rabbits, pangolins and dromedaries, as though they were triangles, rhombuses, parabolas or dodecahedrons. The rabbits that we see are wan shadows of the perfect 'idea' of rabbit, the ideal, essential, Platonic rabbit, hanging somewhere out in conceptual space along with all the perfect forms of geometry. Flesh-and-blood rabbits may vary, but their variations are always to be seen as flawed deviations from the ideal essence of rabbit.
Dawkins introduces the evolutionary (and revolutionary) alternative that animals are instead just snapshots on a continuum of variation over the millions of years. A "rabbit" is not a definition locked-in for eternity, and so if we were to trace the lineage of rabbits back through time, we'd see a gradual progression of creatures looking less and less like the rabbits we know today.
The next step in understanding evolution is to realise it puts everything on a single family tree, so one can trace through history and genealogy from one creature to any other plant or animal at any time in history.
Dawkins calls this explanation of tracing the genealogies between any two creatures a "thought experiment", and that is what it is. It is a useful explanation of the theory, but that in itself is not proof of the theory. It is a useful aid to understanding some important evolutionary concepts.
By talking about essentialism, Dawkins seems to imply that a big barrier to accepting evolution is not the scientific evidence for or against, but people's mental models that we use to interpret the world. He is not talking about scientific evidence at this stage, but gently introducing the reader to a different way of thinking. I'm okay with that—you have to start somewhere, and one may as well start with explaining the essential theoretical concepts of the evolutionary model. As for actual hard data to support the idea, that still promises to come later.
Dawkins refrains from making a connection between Platonic essentialism and creationist world views. I think that's very interesting, because I expected him to portray creationists as having this view. To put the question in other terms, do creationists believe in a "fixity of the species" or "immutability of species"? Here's where it gets interesting, because many creationists (both young and old earth) are very comfortable with the idea that species and animal groups can and do vary. The idea of essentialism—either affirmed or denied—doesn't usefully explain the creationist world-view. Creationists do believe in an original creation, in the sense of what God originally made, being good and wonderful. But creationists don't believe that there is an "ideal rabbit" that is "locked in" forever more, with never a gene to vary—that is manifestly obvious from observing the world around us. Within a few generations of plants or animals, we can observe the scope for variation of a group of animals. As Darwin himself famously observed the finches of the Galapagos islands, populations can constructively vary in response to the environment. The Christian scientist Mendel made the first inroads to understanding the underlying genetics that make this feat possible. Essentialism? Fixity of the species? That doesn't describe the creationist view. That leads naturally on to the second section of chapter 2.
Sculpting the Gene Pool
In the second part of chapter 2, Dawkins describes the tremendous variation in species that humanity has long been aware of, in the way of artificial selection. He describes the amazing variety of dogs and the variations on the humble cabbage, achieved by human artificial selection of desirable traits. He describes the nature of this genetic variation—the gene pool within a population, being shuffled like cards as generations breed, and the favoured traits being selected (artificially in this case). Dawkins explains how it is that genes don't "blend", losing variety over time, but the richness of genetic variation is preserved in a population.
In fact, of course, anybody can plainly see that there is no such intrinsic tendency for variation to decrease in a population. Mendel showed that this is because when paternal genes and maternal genes are combined in a child (he didn't use the word 'gene', which wasn't coined until 1909), it is not like blending paints, it is more like shuffling and reshuffling cards in a pack.
These principles of genetic variation in a population are undisputed by creationists. The main point that Dawkins seeks to make in the chapter is the tremendous variation that can be achieved in such a short time; only a few generations of breeding and selection can yield astounding variation. I agree, it is astounding.
The main point I want to draw out of domestication is the astonishing power to change the shape and behaviour of wild animals, and the speed with which it does so. Breeders are almost like modellers with endlessly malleable clay, or like sculptors wielding chisels, carving dogs or horses, or cows or cabbages, to their whim... The relevance to natural evolution is that, although the selecting agent is man and not nature, the process is otherwise exactly the same.
This is where Dawkins surprises me. "Endlessly malleable clay"? This glosses over what surely is a crucial feature of the process: selective breeding selects favourable genes from an existing gene pool. The variety that gene pool can produce is indeed astounding, but it is not endless. Genes allow for finch beaks to vary in size, but not endlessly. If breeders artificially selected finches for maximal beak sizes, could the sizes increase endlessly? Not at all—an increase could undoubtedly be obtained fairly quickly, but breeders would soon face a prospect of diminishing returns. Is there a boundary to what breeders can achieve? Certainly. What determines the boundary? The extent of the population's gene pool.
The scope of variation hidden in a population's gene pool is wondrous. But the gene pool, like Dawkin's pack of cards analogy, is finite. A poker player will never be fortunate enough to get five of a kind; finches will never get hummingbirds' wings or storks' legs, even by the most determined breeder. The most determined and well-financed dog breeder could never end up with a cat.
"But you forget about mutations!" I hear you say. We will come to that later. But for this chapter, Dawkins overstates the capacity of artificial and natural selection. After clearly describing the process of natural selection from a gene pool, he misrepresents how it fits into evolutionary theory. First, he says this:
But when there is a systematic increase or decrease in the frequency with which we see a particular gene in a gene pool, that is precisely and exactly what is meant by evolution.
Really? If that is precisely and exactly what evolution is, all creationists could happily say, "I believe in evolution"! But evolution claims much more than this, and it requires other mechanisms besides simple selection of a gene pool (to inject genuinely new genetic material—e.g. mutations) to achieve its claims.
Next, he speaks as though the amazing variation within a population's gene pool has no limits.
If so much evolutionary change can be achieved in just a few centuries or even decades, just think what might be achieved in ten or a hundred million years.
Viewing the process over centuries, it is no empty fancy that human dog breeders have seized dog flesh like modelling clay and pushed it, pulled it, kneaded it into shape, more or less at will.
If only breeders' successes were indeed limitless. Then by now, surely 100 metre sprinters at the Olympics would have broken the 5 second mark. Surely Przewalski's horse would have been domesticated. Surely blue roses wouldn't be a symbol of the unattainable. As Wikipedia says:
Blue roses, often portrayed in literature and art as a symbol of love and prosperity to those who seek it, do not exist in nature as a result of genetic limitations being imposed upon natural variance.
Should this temper Dawkins' optimism? I believe it should. Dawkins is glossing over an essential limitation of evolution. While selection of a population's gene pool can achieve amazing variation in a short time, that variation has definite boundaries, depending on the characteristics of the gene pool.
Creationists see the gene pool and the capacity for natural selection as being a consequence of God's providence, which endows populations with a greater resilience against environmental change. Thus by God's providence, Darwin's finches could more easily flourish on the Galapagos Islands. It allows humans an opportunity to domesticate many animals, and select qualities that can be used for the benefit of humanity. But gene pools are finite, and bounded.