Evolution__3rd_Edition

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CHAPTER 12 / Adaptations in Sexual Reproduction 341
a sex ratio a is easy to measure. The sex ratio will therefore likely stay in the vanguard
of evolutionary research for some time to come.
12.6 Different adaptations are understood in different
levels of detail
We have looked at the function of sex, sexual selection, and the sex ratio, as three
related examples of research on adaptation. In each case, the research has advanced to a
different stage.
The problem of sex is still unsolved. Until recently, the main work has been theoretical,
aiming to build a model in which some hypothesized advantage to sex is large
enough to outweigh the 50% cost. We now have two reasonably well worked out theories
(the mutational and parasitic theories) and research is moving on to an empirical
phase.
In the case of sexual selection, the main theories of female choice have been around
for some time. They provide a satisfactory abstract explanation for organs such as the
peacock’s tail. The full repertoire of techniques a model building, experiment, comparative
methods a are being used. At a detailed natural history level, many questions
remain unanswered. We do not know whether the abstract ideas correctly explain the
full natural variety of sexual behavior and dimorphism, and the ideas are not easy to
test.
The theory of sex ratio is still further advanced. The relation between facts and
theories is good. We have not only a general abstract theory as for sexual selection,
but the theory also makes quantitative predictions and suggests a number of types of
test in special cases. Several of the tests have been followed up, and the fit of results to
predictions suggests that the theory stands a good chance of being correct.