: 1. Explaining the Very Improbable ::: Dawkins addresses the argument from design. He emphasizes that natural selection is nonrandom (since only adaptive traits are selected for) and cumulative (as adaptive traits accumulate). :2. Good Design ::: Dawkins discusses the evolution of
echolocation in
bats. Many animals have some ability to navigate by sound. Such abilities can be honed by natural selection to produce the sophisticated sonar seen in bats. : 3. Accumulating Small Change :::Dawkins writes that "We have seen that living things are too improbable and too beautifully 'designed' to have come into existence by chance. How then, did they come into existence? The answer, Darwin's answer, is by gradual, step-by-step transformations from simple beginnings. ... Each successive change in the gradual evolutionary process was simple enough,
relative to its predecessor, to have arisen by chance. But the whole sequence of cumulative steps constitutes anything but a chance process. ... The cumulative process is directed by non-random survival." :::Dawkins illustrates the difference between the potential for the development of complexity as a result of pure randomness, as opposed to that of randomness coupled with cumulative selection. He demonstrates this by the example of the
weasel program. Dawkins then describes his experiences with a more sophisticated
computer simulation of artificial selection implemented in a program also called
The Blind Watchmaker, which was sold separately as a teaching aid. :::The program displayed a two-dimensional shape (a "biomorph") made up of straight black lines, the length, position, and angle of which were defined by a simple set of rules and instructions (analogous to a genome). Adding new lines (or removing them) based on these rules offered a discrete set of possible new shapes (mutations), which were displayed on screen so that the user could choose between them. The chosen mutation would then be the basis for another generation of biomorph mutants to be chosen from, and so on. Thus, the user, by selection, could steer the evolution of biomorphs. This process often produced images which were reminiscent of real organisms, for instance
beetles, bats, or
trees. Dawkins speculated that the unnatural selection role played by the user in this program could be replaced by a more natural agent if, for example, colourful biomorphs could be selected by butterflies or other insects, via a touch-sensitive display set up in a garden. : 4: Making Tracks Through Animal Space ::: Dawkins looks at the
evolution of the eye. Many animals have a patch of light-sensitive cells. Natural selection would favor the formation of a "cup" which can detect direction. From there you can get a
pinhole camera eye, as seen in the
chambered nautilus. The addition of a lens results in the
cephalopod eye. "For each of these types of eye, stages corresponding to evolutionary intermediates exist as working eyes among modern animals." Any improvements would be favored by natural selection. In fact, eyes have evolved several times independently, an example of
convergent evolution. He returns to echolocation, noting that "Any animal that can hear at all may hear echoes. Blind humans frequently learn to make use of these echoes. A rudimentary version of such a skill in ancestral mammals would have provide ample raw material for natural selection to build upon, leading by gradual degrees to the high perfection of bats." Echolocation also seems to have evolved several times independently, another example of convergent evolution. :5. The power and the archives ::: Dawkins looks at
genetics.
Gregor Mendel discovered that inheritance is particulate.
R. A. Fisher united Darwin and Mendel in the
modern synthesis. :6. Origins and miracles :::Dawkins looks at the origin of life, including the work of
Graham Cairns-Smith. :7. Constructive evolution :::Dawkins looks at
evolutionary arms races between predator and prey, and the
Red Queen's hypothesis.
Gene duplication is introduced as a means of increasing a species's genetic capacity. :8. Explosions and spirals :::Dawkins looks at Darwin's concept of
sexual selection, revived by R. A. Fisher. It is thought that peacocks evolved colorful plumage to attract peahens. But the peahens are also passing along genes preferring plumage. This is an example of
linkage disequilibrium, which can lead to runaway evolution. :9. Puncturing punctualism :::Dawkins examines the
punctuated equilibrium theory of
Niles Eldredge and
Stephen Jay Gould. :10. The one true tree of life :::Dawkins examines
molecular taxonomy.
Neutral mutations serve as
molecular clocks that allow us to tell when species diverged. 11: Doomed rivals :::Dawkins examines alternatives to natural selection, like
Lamarckism, and finds them wanting. In an appendix to the 1996 edition, Dawkins explains how his experiences with computer models led him to a greater appreciation of the role of
embryological constraints on natural selection. In particular, he recognised that certain patterns of embryological development could lead to the success of a related
group of species in filling varied ecological niches, though he emphasised that this should not be confused with
group selection. He dubbed this insight
the evolution of evolvability. ==Reception==