In this, the second of Dawkins' popularisations of evolutionary biology, he primarily addresses the so-called "Argument from Design". This argument was most succinctly summed up by the 18th century theologian Willam Paley. He argued that something like a watch, if discovered on a barren heath, would inevitably lead to the conclusion that a watchmaker had been at work. Yet living organisms, which are far more complex than watches, should need a vastly more powerful watchmaker, not the blind forces of Darwin's evolutionary theory.
Dawkins spends the first part of the book thoroughly debunking this position. He shows how random variation, filtered by non-random natural selection, can make incremental changes to the form of a replicating system. This is illustrated with simple comuter-generated entities Dawkins calls "biomorphs". These have only 9 genes, each of which governs a single phenotypic character. The changes made as a biomorph evolves can be traced as a path in 9-dimensional space, one for each gene. Each step along the path must make the descendant biomorphs "better" in some way than the previous generation.
This process of natural selection is the "blind watchmaker" of the title, crafting fit organisms with no plan, no view for the future and no mechanisms more sophisticated than random variation and differential survival.
He then takes us through plausible evolutionary mechanisms for the construction of some particular features, including the eye and the sophisticated sonar system used by bats. With the bats, in particular, he shows that an evolutionary arms race between predator and prey can work to apply significant evolutionary pressure over large amounts of time. This leads naturally both to the bats own impressive ability and to the ability of moths to detect bats and avoid them. This kind of evolutionary arms race often leads to extreme specialisation.
These "tracks through animal space" are considerably more difficult to follow than the ones the biomorphs take, but they are similar in many respects. Each change must not result in an animal less fit than its predecessors or contemporaries, and this often leads to some interesting destinations. Since evolution cannot steer the trajectory of an animal through a disadvantageous part of the space, a lot depends on where you start from. The selection pressures on flatfish are generally similar - lay flat and you wont be seen - but it has lead to two very distinct types of fish. Skates and rays are the "rational" design, bilaterally symmetrical with both eyes on top. However, flounders and plaice started from a different ancestor, already flattened vertically for other reasons. In expanding into the flatfish niche, they lay on their sides, and repeated selection has created a fish with a misshapen skull, both eyes on the same side of the head, and various other features. No rational designer would ever have favoured this layout, but presumably any adaptation towards bilateral symmetry would have been a disadvantage for a fish which had to lay on its side in the sand.
Thus, the blind watchmaker makes mistakes, and these mistakes are very telling. Evolution selects for local maxima of fitness, not necessarily global ones. Returning to the eye, many different types of eye can be found in different creatures, including simple light cells, refractors, reflectors and pinhole cameras, each confined to its local fitness maximum.
The consequences of evolution require that speciation events result in a tree of life with a particular layout, and this is what taxonomists attempt to reconstruct by grouping organisms together at different levels. Taxonomy is a powerful instrument for determining common ancestry.
In conclusion, this book is a valuable introduction to the forces that shape organisms of all kinds, and gives a broad outline of the kinds of features you would expect to find in creatures anywhere. The single most exciting idea you can take from this book is that the diversity of life we see around us is not incredible, but almost inevitable.
Back to the booksSean Ellis
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