Chapter-by-chapter thoughts on Richard Dawkins’ The Greatest Show on Earth: The Evidence for Evolution
by John C. Snider Â© 2009
Chapter 2: Dogs, cows and cabbages
In Chapter 2 Dawkins tackles another of the common “criticisms” that evolution deniers like to whip out: that scientists can’t even agree on a concise definition of “species.”Â This is true to some extent, but Dawkins maintains–and I think he’s right on this one–that our ability to conceptualize “species” is hobbled by our intuitive categorical thinking.Â Dawkins reminds us of Plato’s Forms: the Greek philosopher theorized that idealized versions of everything exist in some higher realm.Â Somewhere there’s the Ideal Dog, of which every real and individual dog is an imperfect manifestation.
Of course, there is no Ideal Dog; there are only populations of dogs, each varying in different degrees from the rest of the population.Â So when we think about evolution, it’s better to think in terms of the “normal curve” along which individuals exist within the overall population.Â It is then a little easier to see two populations of the same species slowly diverging, gradually losing their overlap until, after many, many generations, they no longer overlap–and a new species is born.Â (At least I think this is what he’s saying: I must embarrassedly admit I haven’t had any formal biology education since high school!)
I also like Dawkins’ “Hairpin Thought Experiment.”Â The idea here is to pick any given animal in existence today (Dawkins uses a rabbit), and form an enormously long line, starting with the rabbit’s mother, then grandmother, and on and on, a vast conga line of bunnies stretching back into deep time.Â Eventually, Dawkins points out, you’ll start to see creatures that look less and less “rabbity” and more unfamiliar.Â At some point, you stop examining this lineage and make a “hairpin turn” and begin following another line of progeny from the ancestral pre-rabbit-mammal, and if you know which daughter to follow, slowly, slowly you will find your way by increments to the modern leopard!Â (It should go without saying, of course, that rabbits and leopards, like all living things, share a common ancestor.)
Dawkins also spends some time discussion how human-guided breeding of animals to create various extremes (like chihuahuas, or any other pure breed you could name) illustrates how unguided breeding (through natural selection) can lead, over great swaths of time, to the incredible diversity of flora or fauna we see today.Â I suspect this point may be lost on those who see human-guided breeding as the only way such extremes could have come about: it would have been nice had Dawkins continued the analogy to show how some random environmental factor blindly acted on a population to create some species or other.Â Maybe he will later in the book.
On to Chapter 3…!
Read my thoughts on Chapter 1.