Chapter 3

Evolution and Genetics

Where did we come from?

Human history is relatively short

Evolutionary history is extremely long

Species

A species is a reproductively isolated breeding population More than 95% of all species that have ever

lived are now extinct

Distal and Proximal Causes of Behavior

Distal (ultimate) causes: causes of behavior rooted in evolutionary and genetic

determinants

Proximal (nearby) causes: Causes of behavior that focus on immediate, local,

(psychological and sociological) determinants. Crying behavior shows both distal and proximal causes:

Darwin’s Theory of Evolution

On the Origin of Species by Means of Natural Selection (1859)

Evolution: existing species of life on earth are the end

result of a process of natural selection

Adaptation

Any characteristic that improves the "fit" of a plant or animal with its environment, thereby increasing its chances of transmitting genes to the next generation.

Natural Selection

The means by which organisms adapt to the environment and reproduce differentially.

Selective Pressure Any feature of an environment that allows one

organism to have reproductive advantage over another.

Lamarckian Evolution

The theory that genetic changes can occur in populations through the inheritance of characteristics acquired during a lifetime.

Cataclysmic Disasters

Mass extinction due to natural calamities E.g. asteroid impact resulted in sudden

extinction of the dinosaurs

Genetics and Heredity

Genes The basic units of heredity

Genotype The genetic constitution of an individual

organism

Phenotype The physical expression of features in an

organism that results from the interaction of its genotype with the environment

Mendel’s Experiments:

Breeding peas with dominant and recessive traits results in predictable proportions of offspring

Aa bred with Aa results in 75% dominant phenotype, 25% recessive phenotype

Mendel’s Experiments

Aa Aa

Aa AaAA aa

Note: These three offspring appear identical.

Deoxyribonucleic Acid (DNA)

A double-strand, helix-shaped structure containing genetic material. The basis of the chromosome:

A structure in the nucleus of a cell that carries genetic information

Genetic Relatedness

Degree of Relatedness Individual Organism Percentage of genesshared with you

an identical twin 100%

first degree a sibling (brother or sister) 50a mother or father 50a child 50

second degree a grandparent 25a grandchild 25a half-brother or half-sister 25an aunt or uncle 25a niece or nephew 25

third degree a first cousin 12.5

a stepchild 0 or ?a spouse 0 or ?

Genetic Relatedness

Homo Sapiens has a shared genetic history with all its ancestors

We also have a shared genetic relationship with other animals Up to 98.4% genetic

similarity to some chimpanzee species

Genetic Variability

Meiosis The process of cell division

that produces sex cells (sperm and egg) containing one of each pair of chromosomes

“Crossing over” results in genetic variability

How can genes influence behavior?

Genes can only produce proteins Proteins create structures like the brain

Genes and Environment

Phylogenetic History The evolutionary history of a specific group of

organisms

Ontogenetic History The history of an animal’s entire development, from

fertilization through death

Extragenetic History Information in the form of cultural wisdom, including

oral and written history, that is passed across generations

Nature vs. Nurture

Species-specific behaviors adaptive, innate response

patterns typical of a species

Learning Changes in behavior

resulting from experience

Behavioral Genetics

The study of how genes, interacting with environments, affect behavior

E.g. Emotionality in dogs Breeding fearful basenji dogs with sociable

cocker spaniels results in an F2 pattern of offspring similar to that seen in Mendel’s experiments3/4 Fearful, 1/4 sociable

Fearfulness is a dominant trait

Behavioral Genetics

Obesity in mice

Behavioral Genetics

Obesity in mice Inbreeding heavy mice results in heavier

offspring

An example of a polygenic character A character that varies in a continuous

manner, presumably caused by the effects of many genes

Ethology

The study of species-specific behaviors

Ethologists are interested in instinctive behaviors Patterns of behaviors that are common to a

species

Ethology

Appetitive Behaviors Preliminary activities that precede and lead to

consummatory behaviors

Consummatory Behaviors Innate "survival" behaviors such as copulating

and eating

Imprinting

A highly adaptive innate behavioral process that involves the rapid development of a response to a specific stimulus at a particular stage of development E.g. following behavior in

goslings

Fixed Action Patterns

Programmed sequence of species-specific behaviors that are triggered by a particular stimuli E.g. egg-retrieval in

geese

Fixed Action Patterns

Sign Stimulus A specific environmental stimulus that triggers

innately organized behaviorsE.g. sight of egg

Innate Releasing Mechanism A neural mechanism that triggers an innately

organized motor program

Species-Specific Defense Reaction

An innately organized hierarchy of defense behaviors elicited by signals indicating potential danger E.g. “freezing” and fleeing from danger in rats

Comparative Psychology

The study of the motivation and behavior of animals in order to identify similarities and differences among them

Morgan’s Canon: One should not attribute complex

psychological processes to non-human animals if a simpler explanation is available

Anthropomorphism

The attribution of human characteristics to animals

Zoomorphism

The attribution of animal qualities to humans

Contact Comfort

Harlows Baby monkeys prefer contact with soft

“mother” over “mother” that merely gives food

Harlow picture

Pair Bonding

A strong and enduring affection that unites an infant with a parent Social isolation disrupts pair bonding and

later adult interactions (Harlows)

Neuroethology

The study of the relationship between the nervous system and consummatory behaviors E.g. brain areas controlling song in birds

change in size as a function of hormone levels

Sociobiology

The study of the genetic determinants of social behavior

Evolutionary Psychology The study of human and animal minds and

behavior from the perspective of evolutionary theory.

The “Selfish Gene” - Dawkins

Human behavior can be viewed as an attempt by our genes to propagate themselves

Kin Selection The theory that one promotes the well-being and

inclusive fitness of a genetic relative because of shared genes

Inclusive Fitness The fitness of an individual and related individuals

(who carry many of the same genes)

Altruism

A behavior that helps another individual but may diminish one’s survival or reproductive potential The likelihood of altruism correlates with the

one’s genetic relationship to the individual receiving help

Mating Patterns

Monogamy

Polyandry

Polygyny

Polygandry

Mating Patterns

Parental Investment

Mating patterns are influenced by how much an offspring’s survival costs one parent or another E.g. carrying a child through gestation vs.

providing sperm E.g. time spent guarding mate or offspring

Human Mating Systems