Evolution and the Study of Animal Behavior
2.1 Evolution by Natural Selection favors behavioral adaptations that enhance
Different breeds, same species. Each breed possesses unique trait features with
respect to body size and shape, tail length, head shape, coat, texture, and color.
There are over 200 breeds of dogs
All breeds of dogs have descended from the gray wolf (Canis Lupus), and the
ancestors are a result of human manipulation of the breeding of individuals over the
past 14, 000 years. This is through the selection of individuals that possess certain
traits for a particular breed, called the breed standard.
Many breeds were created for specific tasks
Breeders allow reproduction only among individuals that possessed certain traits
Differences in breed standards over time eventually led to ever-greater differences
among the dog breeds we see today—This process is known as artificial selection
because it is done artificially—that is, by humans.
Similar processes also occur naturally, called Natural Selection: is the differential
reproduction and survivorship among individuals within a population. It is the
mechanism that results in adaptive evolution—Charles Darwin and Alfred Russell
Natural selection occurs because there is variation in traits among individual in a
population, and some traits provide individuals with greater reproductive success
When these traits are heritable, they are passed from parents to offspring.
Natural selection can result in changes in allele frequencies in a population over
time—a process that we recognized as evolution.
The 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 offspring so that offspring 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
Natural Selection: Differential reproduction and survivorship among individuals
within a population. The mechanism that results in adaptive evolution
Heritable: A trait that can be passed from parents to their offspring because of
Evolution: Changes in allele frequency in a population over time
Fitness: The relative survivorship and reproductive success (ability to produce
viable offspring) of an individual
Gene alleles are the basis of phenotypic traits
Natural selection acts on heritable variation among individuals and can result in
changes in allele frequencies and associated trait values in a population.
Traits that confer high fitness increase over time, while those that confer low fitness
When traits are heritable, parents will tend to pass on the traits they possess to
their offspring via their shared alleles. Many behavioral traits that have been studied
are in fact heritable, including mating behavior, feeding behavior, overall activity
level, and aggression.
Deoxyribonucleic acid (DNA) condenses into chromosomes during mitosis and
Specific stretches of DNA contain genes, which code for polypeptides (i.e. proteins)
that have a variety of functions.
Alleles are different versions of a gene
The locus is the physical location of an allele on a chromosome, and each may have a
If the alleles are the same, then the organisms are homozygous for these alleles; if
the alleles are different, then they are heterozygous.
During sexual reproduction, each parent contributed only one of its alleles.
Therefore, offspring have different alleles combinations than their parents During meiosis, homologous chromosomes line up in pairs. During this time, they
can exchange segments of DNA, known as crossing over. This process results in
novel combinations of DNA that increase genetic diversity.
Measures of Heritability:
Traits must be heritable for natural selection to act on them. How do we determine
the heritability of a trait? Two methods are commonly used:
1.) Parent-Offspring 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 he trait values of offspring should be similar to the trait
values of their parents: there should be a positive relationship between
offspring and parent trait values.
Parent-Offspring Regression: A statistical technique used to examine the
similarity between parents and their offspring in the traits that they possess.
2.) The Selection Experiment: method, different groups of individuals are
subjected to differential selections 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.
Selection Experiment: An experiment in which different groups of individuals are
subjected to differential selection on a trait.
The Great Tit Exploratory Behavior:
Examined the heritability of exploratory behavior in free-living great tits.
The great tit is a small, colorful passerine bird found throughout much of Europe
It is a common inhabitant of woodlands, parks, and gardens where it feeds on
insects and seeds
It nests in tree cavities as well as nest boxes
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)
Are these personality traits heritable?
Experiments used birds from two populations in the Netherlands as part of a long-
term research project. Put them in an artificial wooden area with five trees to record the flights and hoped
that the birds took
There was a positive correlation between a mother’s exploratory behavior and the
Separated adults into two groups for the selection experiment for fast and slow
One group contained birds with the lowest exploratory behavior, while the other
contained those birds with the highest exploratory behavior. The nine individuals
both male and female with low and high scores for each generation were then
selected for breeding.
This took four generations. By this time, the average exploratory score for
individuals in the high line was over four times higher than that for individuals in
the slow line. This result indicates that exploratory behavior is heritable/ has a
1.) Offspring resemble their parents in this behavior
2.) Artificial selection on exploratory behavior produced significant differences
in the two artificially selected lines.
Variation within a population:
Through the process of natural selection, populations evolve
This evolution requires variation among individuals in the traits they possess
Variation caused by: Genetic composition—each generation introduces new genetic
variation into populations through gene recombination, the immigration of new
alleles into a population, and mutations.
Individuals in any population differ genetically; they will also tend to vary in their
First, Changes in environmental conditions can change the fitness of different traits
and maintain much variation in the frequencies of different alleles
Secondly, many behaviors develop as a consequence of both genetic and
environmental effects; therefore, even close relatives with similar genes often
exhibit very different behavior as adults when they are exposed to different
environmental conditions as juveniles
Third, many complex behaviors require learning and therefore are modified with
experience. Individuals will differ in experience over the course of a lifetime;
therefore, there will be observable differences in their behavior as well.
Example: Bees need to learn how to best extract nectar and pollen from flowers and
then transport them efficiently back to their colony. Feeding performance, or their
rate of food delivery to the colony, increases dramatically over the first four days of
foraging activity as a result of trial-and-error learning.
Fourth, there might be little or no variation in fitness over a wide range of
behaviors. For example: 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. For many species in many habitats, individuals will experience the same fitness whether
they disperse in any direction. When this is true, it is expected that there will be
much variation in dispersal direction within a population.
For example: Eastern screech owls: Studied dispersal direction. It was found that
there was no particular pattern with respect to dispersal direction, which is to be
expected is characteristics that determine territory quality and fitness are not
associated with compass direction relative to the natal