Chapter 2: Evolution and the Study of Animal Behaviour
2.1 Evolution by Natural Selection Favors Behavioural Adaptations
That Enhance Fitness
1. Over many generations, human breeders have selected individuals that possess
certain traits for a particular breed, called the breed standard. Many breeds were
created for specific tasks: terriers to hunt vermin, retrievers to find and retrieve
hunters’ birds, and greyhounds to hunt swift prey.
2. Differences in breed standards over time eventually led to evergreater differences
among the dog breeds we see today. This process is known as artificial selection
because it is done “artificially”— by humans.
3. Natural selection is the differential reproduction and survivorship among
individuals within a population. It is the mechanism that results in adaptive
4. Darwin was not the first to suggest that species evolve, but he (along with Alfred
Russell Wallace) was the first to describe the plausible mechanism, natural
selection, by which evolution can occur.
5. Natural selection occurs because there is variation in traits among individuals in
a population, and some traits provide individuals with greater reproductive
1. When these traits are heritable, they are passed from parents to off spring.
Natural selection can result in changes in allele frequencies in a population
over time—a process that we recognize as evolution.
6. In his book On the Origin of Species (1859), Darwin articulated three conditions
required for evolution by natural selection:
1. Variation exists among individuals in a population in the traits they possess.
2. Individuals’ different traits are, at least in part, heritable. Traits can be passed
from parents to their off spring so that off spring resemble their parents in the
traits they possess.
3. Traits confer differences in survivorship and reproduction, a measure we call
fitness: individuals with certain traits will have higher fitness, while those
with other traits will have lower fitness relative to one another. Therefore, the
fitness of individuals is not random; it is based on the traits they possess.
7. Many behavioral traits that have been studied are in fact heritable, including
mating behavior, feeding behavior, overall activity level, and aggression (Stirling,
Réale, & Roff 2002).
MEASURE OF HERITABILITY
8. Parentoff spring regression analysis examines the similarity between parents
and their offspring in terms of the traits they possess. If a trait has a genetic
basis, then the trait values of off spring should be similar to the trait values of
their parents: there should be a positive relationship between off spring and
parent trait values. In this method, off spring trait values are plotted against
parent trait values, and the slope of the resulting regression indicates the
heritability of the trait.
9. In the selection experiment method, different groups of individuals are subjected
to differential selection on the trait in question. If artificial selection acting on a
trait results in changes in that trait value in subsequent generations, then the trait has a genetic basis.
GREAT TIT EXPLORATORY BEHAVIOUR
10. Niels Dingemanse and his colleagues examined the heritability of exploratory
behavior in freeliving great tits ( Parus major ) (Dingemanse et al. 2002).
11. Previous work indicated that individuals exhibit differences in their exploratory
behavior when placed in novel environments: some actively explore their new
environment quickly (bold individuals), while others are more reticent and slower
to explore (shy individuals) (Verbeek, Drent, & Wiepkema 1994; Drent &
1. There was a significant positive correlation between a mother’s exploratory
score and that of her off spring, demonstrating a genetic basis for differences
among individuals in this behavior.
12. The research team found strong changes in exploratory behavior of the two lines
in the selection experiment over four generations. By the fourth generation, the
average exploratory score for individuals in the high line was over four times
higher than that for individuals in the slow line (Drent, van Oers, & van
Noordwijk 2003) (Figure 2.3).
1. This result indicates that exploratory behavior is heritable. Together, the
results of these two experiments conclusively demonstrate that exploratory
behavior in great tits has a genetic component.
2. This conclusion was based on two pieces of evidence:
1. Offspring resemble their parents in this behavior, and
2. Artificial selection on exploratory behavior produced significant
differences in the two artificially selected lines.
VARIATION WITHIN A POPULATION
13. Each generation introduces new genetic variation into populations through gene
recombination, the immigration of new alleles into a population, and mutations
1. Changes in environmental conditions can change the fitness of different traits
and so maintain much variation in the frequencies of different alleles.
14. Many behaviors develop as a consequence of both genetic and environmental
effects. Thus, even close relatives (with similar genes) oft en exhibit very different
behavior as adults when they are exposed to different environmental conditions as
15. Many complex behaviors require learning and so are modified with experience.
Because individuals will differ in experience over the course of a lifetime, we will
observe differences in their behavior as well.
16. There might be little or no variation in fitness over a wide range of behaviors.
One example is dispersal behavior. Dispersal is the process of moving away from
the natal area, or place of birth, to find an adult breeding area or territory.
17. The fitness of a trait (behavior) may be related to its frequency in a population.
When rare, the behavior may yield high fitness, but when common, it may result
in much lower fitness.
18. Individuals in all populations typically differ in size, nutritional status, health,
and other traits. These differences can lead to significant variation in behaviors.