Evolution__3rd_Edition

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Study and review questions
1 Use Figure 4.1b to construct a life table, like Table 4.1,
for cod. (Use the densities per meter squared as numbers;
and you may prefer to ignore the right-hand column, for
daily mortality rates, which require logarithms.)
2 (a) Review the four conditions needed for natural
selection to operate. (b) What would happen in a
population in which only conditions 1, 2, and 3 were
satisfied? (c) And in one in which only 1, 3, and 4 were
satisfied?
3 Variation in reproductive success has been found in all
populations in which it has been measured. Why is this
observation alone insufficient to show that natural
selection operates in all populations?
4 It is occasionally suggested that mutation is adaptively
directed rather than random. Think through what a
genetic mechanism of adaptively directed mutation
would have to do. For each component of the
mechanism, how plausible is it that it could really exist?
CHAPTER 4 / Natural Selection and Variation 91
in this text. See Holmes (2000a) for the HIV possibilities. Biases at the molecular level
in the mutation process are set to be revealed by genomic data (see, for instance, Silva &
Kondrashov 2002), and Mukai-style mutation–accumulation experiments, discussed
in Chapter 12 of this text.
5 What sort of selection is taking place in populations a,
b, and c in the graph?
Fitness
(a) (b) (c)
Brain size
Fitness
6 [These question are more for further thought than
review of chapter content.] (a) On average only two
offspring survive per parental pair: why therefore does
every pair in the population not produce exactly two
offspring (rather than the more variable reproductive
success we see in nature)? This would lead to the same
end consequence. (b) Why in some species is the
“excess” far greater than in others?
Fitness
Brain size Brain size