The Greatest Show on Earth: The Evidence for Evolution

Here are some highlights from this book by Richard Dawkins:

* 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.

* Something funny happens to the gene pools of domestic dogs. Breeders of pedigree Pekineses or Dalmatians go to elaborate lengths to stop genes crossing from one gene pool to another. Stud books are kept, going back many generations, and miscegenation is the worst thing that can happen in the book of a pedigree breeder. It is as though each breed of dog were incarcerated on its own little Ascension Island, kept apart from every other breed. But the barrier to interbreeding is not blue water but human rules.
Geographically the breeds all overlap, but they might as well be on separate islands because of the way their owners police their mating opportunities. Of course, from time to time the rules are broken. Like a rat stowing away on a ship to Ascension Island, a whippet bitch, say, escapes the leash and mates with a spaniel. But the mongrel puppies that result, however loved they may be as individuals, are cast off the island labelled Pedigree Whippet. The island itself remains a pure whippet island. Other pure-bred
whippets ensure that the gene pool of the virtual island labelled Whippet continues uncontaminated. There are hundreds of man-made ‘islands’, one for each breed of pedigree dog. Each one is a virtual island, in the sense that it is not geographically localized. Pedigree whippets or Pomeranians are to be found in many different places around the world, and cars, ships and planes are used to ferry the genes from one geographical place to another. The virtual genetic island that is the Pekinese gene pool overlaps geographically, but not genetically (except when a bitch breaks cover), with the virtual genetic island that is the boxer gene pool and the virtual island that is the St Bernard gene pool.

* You want high milk yield in cows, orders of magnitude more gallons than could ever be needed by a mother to rear her babies? Selective breeding can give it to you. Cows can be modified to grow vast and ungainly udders, and these continue to yield copious quantities of milk indefinitely, long after the normal weaning period of a calf. As it happens, dairy horses have not been bred in this way, but will anyone contest my bet that we could do it if we tried? And of course, the same would be true of dairy humans, if anyone wanted to try. All too many women, bamboozled by the myth that breasts like melons are attractive, pay surgeons large sums of money to implant silicone, with (for my money) unappealing results. Does anyone doubt that, given enough generations, the same deformity could be achieved by selective breeding, after the manner of Friesian cows?

* If you see an animal feeding, you can measure its flight distance by seeing how close it will let you approach before fleeing. For any given species in any given situation, there will be an optimal flight distance, somewhere between too risky or foolhardy at the short end, and too flighty or risk-averse at the long end. Individuals that take off too late when danger threatens are more likely to be killed by that very danger. Less obviously, there is such a thing as taking off too soon. Individuals that
are too flighty never get a square meal, because they run away at the first hint of danger on the horizon. It is easy for us to overlook the dangers of being too risk-averse.

Natural selection will work on the flight distance, moving it one way or the other along the continuum if conditions change over evolutionary time. If a plenteous new food source in the form of village rubbish dumps enters the world of wolves, that is going to shift the optimum point towards the shorter end of the flight distance continuum, in the direction of reluctance to flee when enjoying this new bounty.

Something like this evolutionary shortening of the flight distance was, in Coppinger’s view, the first step in the domestication of the dog, and it was achieved by natural selection, not artificial selection. Decreasing flight distance is a behavioural measure of what might be called increasing tameness.

* Selection – in the form of artificial selection by human breeders – can turn a pye-dog into a Pekinese, or a wild cabbage into a cauliflower, in a few centuries. The difference between any two breeds of dog gives us a rough idea of the quantity of
evolutionary change that can be achieved in less than a millennium.

* evolutionary scientists are in the position of detectives who come late to the scene of a crime. To pinpoint when things happened, we depend upon traces left by time-dependent processes…

* A tree-ring clock can be used to date a piece of wood, say a beam in a Tudor house, with astonishing accuracy, literally to the nearest year. Here’s how it works. First, as most people know, you can age a newly felled tree by counting rings in its trunk…

* Varves are layers of sediment laid down in glacial lakes. Like tree rings, they vary seasonally and from year to year, so theoretically the same principle can be used, with the same degree of accuracy. Coral reefs, too, have annual growth rings, just like trees. Fascinatingly, these have been used to detect the dates of ancient earthquakes. Tree rings too, by the way, tell us the dates of earthquakes.

* What would be evidence against evolution, and very strong evidence at that, would be the discovery of even a single fossil in the wrong geological stratum. I have already made this point in Chapter 4. J. B. S. Haldane famously retorted, when asked to name an observation that would disprove the theory of evolution, ‘Fossil rabbits in the Precambrian!’ No such rabbits, no authentically anachronistic fossils of any kind, have ever been found… Evolution could so easily be disproved if just a single fossil turned up in the wrong date order.

About Luke Ford

I've written five books (see Amazon.com). My work has been followed by the New York Times, the Los Angeles Times, and 60 Minutes. I teach Alexander Technique in Beverly Hills (Alexander90210.com).
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