Evolution__3rd_Edition

312 PART 3 / Adaptation and Natural Selection
Further reading
Study and review questions
1 Give examples of adaptations that benefit:
(a) both the individual organism and the species that the
organism belongs to; (b) the individual organism, but
at a cost to its species; (c) a local group of organisms, at
a cost to its individual members; and (d) a small genetic
system, at a cost to the organism containing it.
2 What is (are) the main theoretical factor(s) in models
of group versus individual selection that determine
whether individual or group adaptations tend to evolve?
3 In the measurements of Woolfenden and Fitzpatrick,
the average number of young birds produced by a nest of
scrub jays with helpers is 2.2 and the average number by
a nest without helpers is 1.24. The average number of
helpers present, for the nests with helpers, is 1.7. What
The multiauthor book edited by Keller (1999) contains chapters by expert authors on
most of the themes in this chapter.
On segregation distorters, I have written a popular book (Ridley 2001) that includes
an account of them and the reasons that Haig and others have suggested to explain why
they are rare. The book has references to the original literature. A further example has
been found in the eye-stalk flies, illustrated in Plate 5 (between pp. 68 and 69), where
a driving sex chromosome shrinks the eye stalks (Wilkinson et al. 1998). Various
subcellular entities provide a level between the “gene” and “cell” levels in this chapter.
Wolbachias are an example, and they are the subject of a newspiece in Nature July 5,
2001, pp. 12–14. Mitochondria are another example, and they enjoy an amazing system
of multilevel selection, discussed by Rand (2001). (I also discuss selection in mitochondria
in Ridley (2001).) On kin selection, the fundamental works are included
in volume 1 of Hamilton’s (1996) collected papers; Dawkins (1989a) is more introductory;
Clutton-Brock (2002) is a review; and Woolfenden & Fitzpatrick (1990) is
about the Florida scrub jay. Sober & Wilson (1998) is about group selection.
For replicator selection, and the relation between the two senses of selection unit, see
Dawkins (1982, 1989a), Gould (2002b), Maynard Smith (1987), and Williams (1966,
1992), who also refer to the prior literature.
values for b and c can be estimated from this data? If the
helpers are brothers or sisters of the individuals they are
helping, does kin selection favor helping?
4 In both kin selection and pure group selection,
adaptations often evolve that benefit the local group.
What key difference is there between the kinds of groups,
and the plausibility of the two processes?
5 Does the fact that individual selection is normally
more powerful than group selection, benefit the average
individual in a group?
6 What is the unit of selection, in the sense of a
replicator, in: (a) a species that reproduces asexually;
and (b) a species in which there is no recombinational
crossing-over at meiosis?
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