Biology Reference
In-Depth Information
eye anatomy across mammals, fish, birds and eels, suggesting that the variation is
because each species has an eye that is more suitable for the environment in
which it lives. Paley's explanation for this fit to the environment was that this
provided evidence for the 'adapting hand' of an intelligent designer who knew
'the most secret laws of optics', and that this provided proof of a benevolent deity.
As explained in Chapter 1, Darwin (1859) showed that the appearance of
design could arise though natural selection and does not require a divine designer.
Importantly, Darwin's theory of natural selection explained both the process (or
dynamics) by which adaptation occurs and how this leads to the appearance of
design. The process is that heritable characters associated with greater
reproductive success will be selected for and accumulate in natural populations.
This leads to the apparent purpose of adaptation, that organisms will appear as if
they were designed to maximize their reproductive success (fitness).
Since Darwin, there have been two major conceptual advances in the study of
adaptation. Firstly, Fisher (1930) united Darwin's theory with Mendelian
genetics by showing how natural selection could be described by changes in
gene frequencies. He showed that genes associated with greater individual
fitness will increase in frequency and that this would lead to an increase in
mean fitness, such that individuals would appear as if they had been designed to
maximize their fitness. Secondly, as discussed in Chapter 11, Hamilton (1964)
showed that consequences for relatives have to be factored in, and that the
fitness which organisms should appear designed to maximize is inclusive fitness,
not just direct reproductive success. Since then, the field of behavioural ecology
has provided one of the most fertile testing grounds for testing Darwin's theory.
approach. Put another way, the empirical success of the ESS approach has shown that
it is often reasonable to ignore the possibility of genetic conflicts within individuals.
Furthermore, even in cases where genetic conflicts are important, this is usually most
easily discovered by deviations between ESS theory and empirical data.
Group selection
At the beginning of the topic, we more or less dismissed group selection as a viable alternative
to selection acting on individuals or selfish genes. We acknowledged that it could in principle
work, but suggested that the conditions for group selection to be a powerful evolutionary
force were not likely to be met in nature very often. However, this is not a universally
accepted point of view. Every so often, papers or topics claim that group selection is more
important than we thought, can explain things that cannot be explained by selection at the
individual level, and has been overly rejected (Sober & Wilson, 1998; Nowak, 2006;
Traulsen & Nowak, 2006; Wilson & Wilson, 2007). How should we treat such claims?
One point to bear in mind from the start is that these claims are based upon models
which are more subtle than the simple 'differential extinction of groups' model discussed
in Chapter 1. The essential feature of these 'new' group selection models is that
populations are divided into groups ('trait groups' or 'demes'), within which selection
