The Greatest Show on Earth - Chapter 2

Summary of Chapter 2: Dogs, Cows, and Cabbages

• Why did it take humans so long to discover evolution?
• Ernst Mayr speculate it was due to Plato essentialism, what we see is a shadow of true reality.  For example, a triangle drawn in the sand is just a shadow of a true, essential triangle
•  In essentialism thinking, there is a "standard rabbit", and all rabbits we see are statistical variations on the standard
• Population thinking is the antithesis of essentialism ... there is no standard rabbit
• All life forms are linked to all other life forms via a chain of intermediates
• Thought experiment ... think of a rabbit, then imagine a chain of ancestors, each link in the chain looking nearly identical, but changing slowly.  Mentally traverse back to the common ancestor of rabbits and leopards.  Perhaps the animal look a little like a shrew, but certainly looked nothing like either a rabbit or leopard.  Now make the hairpin turn and begin walking forward in time, this time taking the path the leads to leopards
• Note there is never a direct cross between a rabbit and a leopard
• "Modern species do not evolve into other modern species, they just share ancestors: they are cousins"
• Humans have very successfully domesticated plants and animals via artificial selection
• The wild cabbage has been turned into broccoli, cauliflower, kohlrabi, kale, brussel sprouts, spring greens, and romanescu
• The wolf has been turned into two hundred breeds of dogs
• All domestic dogs are descended from wolves, not jackals, not coyotes, and not foxes
• What we are really doing is sculpting gene pools
• Gregor Mendel is the father of genetics
• Genes are shuffled between generations
• Darwin came very close to discovering Mendel's law of non-blending genes
• Geographic barriers inhibit gene shuffling.  For example, it will take time for the genes of a rat in Madrid to migrate all the way over to rat populations in Siberia
•  Evolution occurs when there is a systematic increase or decrease of a gene within a gene pool
• A lengthy discussion of dog breeding follows
• Overly muscular cows and pigs are bred by disabling a gene that makes myostatin
• Although morally problematic, there seems little doubt that eugenic breeding of humans could produce superior body-builders, pearl fishers, musicians, poets, etc.
• Next, there's a discussion of computer simulations that can derive new forms based on a human selecting desirable features on each generation, but without an overall master plan or design
• Darwin also discussed artificial selection extensively in Chapter 1 of On the Origin of Species
• Via non-random survival, natural selection over a longer period of time can produce that same affects as artificial selection can in a short timeframe

Kevin's Commentary on Chapter 2

As Dawkins points out in the last paragraph of the chapter, Charles Darwin's first argument in Chapter 1 of On the Origin of Species, Variation Under Domestication, discusses artificial selection that occurs as humans domesticate plants and animals to better serve our purposes.  Thus, it's no surprise that Dawkins would devote his first chapter to the same topic.

The basic argument here is that artificial selection proves that descent with modification can happen, at least under special circumstances.  Thus, we know that it's at least possible.  It doesn't violate any laws of physics, and therefore doesn't require, at least in principle, supernatural guidance.

The thought experiment that Dawkins walks us through, showing how rabbits and leopards are linked via common ancestry, is fascinating to think about.  Dawkins believes that there is sufficient evidence to say that all living creatures are descended from a single ancestor.  If that's true, then any two organisms living today, no matter how different from each other, can be linked together via their ancestry and the hairpin turn.  The greater the difference between the two organisms, the farther back in time one will have to go to find the common ancestor that defines the hairpin turn in the thought experiment.   Try doing this thought experiment yourself using two organisms of your choosing.  When I do it, I try to imagine what the common ancestor might have looked like.

Darwin himself commented on the temptation of trying to imagine an intermediate between two modern species.  It's natural for us to want to do that, and creationists seem to seize upon this as an opportunity to lead the unwary astray.  It is absolutely critical to remember that modern species don't evolve into other modern species.  There is no rabbit-leopard cross.  The common ancestor looked nothing like either.  It might have looked a bit like a shrew, but even then, probably not a modern shrew.