CHAPTER 3: Genetic and Evolutionary Foundations of Behavior

Why Genetics?

•Behavior is hereditary!

•Our environment has shaped our behavior across generations EVOLUTION

•We can learn much about our behavior by studying our animal relatives

•Did you know: we share 98.8% of our genes with chimpanzees?•50% with a banana

How Genes Affect Behavior GENE: the basic physical

unity of heredity

Genes code for protein molecules Structural proteins Enzymes – control the

rate of every chemical reaction in every cell

Genes are composed of long molecules called DNA (deoxyribonucleic acid)

From Cells to Genes…

cell

nucleus

chromosomeDNA

gene

Genes Provide the Code for Proteins

Proteins are comprised of amino acids

Coding vs. “junk” DNA

CODING GENES: code for unique protein molecules

REGULATORY GENES: help activate or suppress specific coding genes and thereby influence the body’s development

Genes do not “code for” behaviors.

Gene/Environment Interaction ENVIRONMENT: every aspect of an individual and his

or her surroundings except the genes themselves.

Environment Genes

Protein Producti

on

Neural functi

on

Behavior

Geneticists use the term genotype to refer to the set of genes that the individual inherits and the term phenotype to refer to the observable properties of the body and behavioral traits.

Genes and Replication: Mitosis

MITOSIS: the form of cell division involved in normal body growth, which produces cells that are genetically identical to each other

MEIOSIS: The form of cell division involved in producing egg or sperm cells, which results in cells that are genetically dissimilar and that each have half the number of chromosomes of the original cell.

The Genetic Diversity of Offspring

ZYGOTE: The single cell that is formed when an egg and sperm cell unite

Consequences of Gene Pairing

LOCUS: a position on a chromosome that contains the DNA of a single gene

ALLELES: different genes that can occupy the same locus on a pair of chromosomes and can potentially pair with one another

Homozygous vs. heterozygous

Dominant vs. recessive

Consequences of Gene Pairing

Mendelian Genetics

Gregor Mendel, Mid-19th Century

Mendelian Genetics

Polygenic Characteristics POLYGENIC CHARACTERISTICS: any trait or

characteristic for which the observed variation is affected by many genes

SELECTIVE BREEDING: the mating of those members of a strain of animals or plants that manifest a particular characteristic to affect the genetic makeup of future generations of that strain

Evolution by Natural Selection

NATURAL SELECTION: selective breeding that results from the obstacles to reproduction that are imposed by the natural environment

Genetic Variability

1. Meiosis

• Genes are reshuffled during DNA recombination and meitotic division

2. Mutations

• Errors that occasionally and unpredictably occur during DNA replication, producing a “replica” that is different from the original

Environmental Influence on Natural Selection Evolution is contingent on

environmental change

Evolution can progress slowly, rapidly, or almost not at all

More complex changes require much more time

All species are to varying degrees similar to one another because of common ancestry, and all species are to some degree unique because natural selection has adapted each species to the unique aspects of the environment in which it lives and reproduces.

Evolution in Action

Before the industrial revolution, a uniformly dark variant of the peppered moth made up 2% of the species. After the industrial revolution, 95% of peppered moths showed this dark coloration.

Skinks living on the coast tend to lay eggs. Those skinks living in the cooler mountains tend to give birth to live young.

The Blue Moon Butterfly of the Samoan islands was being attacked by a parasite which destroyed male embryos. This led to a gender imbalance whereby males made up only 1% of the butterfly population. However, within ten generations (~1 year) males had returned to 40% of the population.

Over time the bacteria have become far more efficient at growing under the conditions used. One of the populations developed the ability to utilize citrate as a nutrient.

• Malaria• MMR

Mistaken Beliefs about Evolution

1. Evolution has foresight

2. We can compare organisms based on their evolutionary path

3. Natural selection is a moral force

Functionalism

FUNCTIONALISM: a school of psychological thought, founded by William James and others, that focuses on understanding the functions, or adaptive purposes, of mental processes.

• Why do giraffes have long necks?

• Why do male songbirds sing?

• Why do humans have the ability to

learn language?

Functionalistic Explanations of Behavior

Ultimate Explanation

Functional explanations at the evolutionary level; that is, how the behavior plays or played a role in survival and reproduction

Proximate Explanation

Explanations that deal with the immediate environmental conditions or the mechanisms within the individual that cause the behavior to occur

Limitations on Functionalist Thinking

1. VESTIGIAL CHARACTERISTICS: inherited characteristics of anatomy or behavior that are no longer useful to the species but were presumably useful at an earlier time in evolution

• E.g. appendix, grasp reflex

2. Some traits are side effects of natural selection for other traits

Limitations on Functionalist Thinking

3. Some traits result simply from chance

• Variation due to chance alone without selection is known as GENETIC DRIFT

4. Evolved mechanisms cannot deal effectively with every situation

Species-Typical Behaviors in Humans

• Any behavior pattern that is so characteristic of a given species of animal that it can be used to help identify that species

• However, these behaviors are not rigid and uninfluenced by learning!

The Role of Learning in Species-Typical Behaviors

Walking Language

Biological Preparedness

BIOLOGICAL PREPAREDNESS: organisms have physical and anatomical structures that predispose them to engage in certain (species-specific) behaviors

The environment

also plays a role!

Cross-Species Comparisons of Species-Typical Behaviors

HOMOLOGY: any similarity among species that exists because of the species’ common ancestry

Cross-Species Comparisons of Species-Typical Behaviors

ANALOGY: any similarity among species that is not due to common ancestry but has evolved independently because of some similarity in their habits or lifestyles

Evolutionary Origin of Two Human Smiles

Evolutionary Analyses of Mating Patterns

POLYGYNY

• One male mates with more than one female

POLYANDRY

• One female mates with more than one male

MONOGAMY

• One male mates with one female

POLYGYNANDRY

• Members of a group consisting of more than one male and more than one female mate with one anther

Parental Investment

The time, energy, and risk to survival involved in producing, feeding and otherwise caring for each offspring

In general, for species in which parental investment is unequal, the more parentally invested sex will be (a) more vigorously competed for than the other and (b) more discriminating than the other when choosing mates

Mating Patterns and Parental Investment

POLYGYNY•High female and low male parental investment•Females choose the best males•Males must try and mate with as many females

POLYANDRY•High male and low female parental investment•Tend to be egg layers•Females are more aggressive courters

MONOGAMY•Equivalent male and female parental investment•Requires two parents for successful child-rearing•No size or strength differences between males and females

POLYGYNANDRY•Related to investment in the group•Permits groups of males and females to live in harmony•Paternity confusion

Human Mating Patterns

Humans fall on the boundary between monogamy and polygyny

Long-term mating bonds

Sex Differences in Aggression

AGGRESSION: fighting and threats of fighting among members of the same species

In primates, males are more aggressive than females

These behaviors are

advantageous (evolution is not a moral force)

Violence in Humans

Humans are no exception to aggression and violence

Cross-culturally, men are more aggressive than women (sexual jealousy)

Exception: female bonobos

Patterns of Helping HELPING: any behavior that increases the survival

chance or reproductive capacity of another individual

COOPERATION: a type of helping behavior in which interaction among two or more individuals increases the survival chance or reproductive capacity of each individual involved in the interaction E.g. living in groups or colonies

Altruism

ALTRUISM: a type of helping behavior in which an individual increases the survival chance or reproductive capacity of another individual while decreasing its own survival chance or reproductive capacity

Kin Selection Theory of Altruism

Apparent acts of altruism have come about through natural selection because such actions are disproportionately directed toward close genetic relatives and thus promote the survival of others who have the same genes

Reciprocity Theory of Apparent Altruism

Apparent acts of altruism have come about through natural selection because they are actually forms of long-term cooperation rather than true altruism

Evolutionary Fallacies

Naturalistic Fallacy

The mistaken belief that whatever is natural (and particularly whatever is a product of natural selection) is right, good or moral

Morality is a product of the human mind!

Beware the phrase “more evolved”

Deterministic Fallacy

The mistaken belief that genes control, or determine, behavior in a manner that is independent of environmental influences

We humans can control our environment and thereby control ourselves!