Natural Selection, Ecology and Behaviour - An Introduction to Behavioural Ecology - page 6

will inherit the characteristics of their successful parents and so, through natural
selection over the generations, organisms will come to be adapted to their environment.
The individuals that are selected, naturally, will be those best able to find food and
mates, avoid predators and so on.
(5) If the environment changes, then new variants may do best and so natural selection
can lead to evolutionary change .

When Darwin formulated his idea he had no knowledge of the mechanism of heredity.
The modern statement of the theory of natural selection is in terms of genes. Although
selection acts on differences in survival and reproductive success between individual
organisms, or phenotypes, what changes during evolution is the relative frequency of
genes. We can restate Darwin's theory in modern genetic terms as follows:

(1) All organisms have genes which code for proteins. These proteins regulate the
development of the nervous system, muscles and structure of the individual, and so
influence its behaviour.
(2) Within a population many genes are present in two or more forms, or alleles, which
code for slightly different forms of the same protein or determine when, where and
how much of the protein is expressed. These will cause differences in development
and function, and so there will be variation within a population.
(3) Any allele that results in more surviving copies of itself than its alternative will
eventually replace the alternative form in the population. Natural selection is the
differential survival of alternative alleles through their effects on replication success.

Selection causes
changes in gene
frequency

The individual can be regarded as a temporary vehicle or survival machine by which
genes survive and replicate (Dawkins, 1976). Because selection of genes is mediated
through phenotypes, the most successful genes will usually be those that are most
effective in enhancing an individual's survival and reproductive success (or that of
relatives, as we shall show later in the topic).

Genes and behaviour

Natural selection can only work on genetic differences, so for behaviour to evolve:
(a) there must be, or must have been in the past, behavioural alternatives in the
population; (b) the differences must be, or must have been, heritable; in other words a
proportion of the variation must be genetic in origin; and (c) some behavioural
alternatives must confer greater reproductive success than others.
Some examples to show how genetic differences between individuals can lead to
differences in behaviour are now discussed. Note the emphasis on the word difference .
When we talk about 'genes for' a particular structure or behaviour, we do not imply that
one gene alone codes for the trait. Genes work in concert and many genes together will
influence an individual's mating preference, foraging, migration and so on. However, a
difference in behaviour between two individuals may be due to a difference in one (or
more) genes. A useful analogy is the baking of a cake. A difference in one word of a
recipe (one versus two spoonfuls) may mean that the taste of the whole cake is different,

Behavioural
differences may
have a genetic
basis