Unit 3C:Biological Bases of Behavior:

Genetics, Evolutionary Psychology, and Behavior

Introduction

• Behavior genetics–Heredity versus the environment

–Nature – genes

–Nurture – environment

Genes: Our Codes for Life• Chromosome – DNA

structures that include genes (46 total – 23 from each parent)

• DNA (deoxyribonucleic acid)

• Genome- the complete instructions for making an organism (human or other)

Twin and Adoption StudiesIdentical Versus Fraternal Twins

• Identical twins – same genes, but maybe not the same # of copies or could have separate placentas

• Fraternal twins – separate altogether, but may carry similar risks for disease- even divorce! (for all twins)

Twin and Adoption StudiesIdentical Versus Fraternal Twins

Twin and Adoption StudiesIdentical Versus Fraternal Twins

Twin and Adoption StudiesIdentical Versus Fraternal Twins

Twin and Adoption StudiesIdentical Versus Fraternal Twins

Twin and Adoption StudiesIdentical Versus Fraternal Twins

Twin and Adoption StudiesIdentical Versus Fraternal Twins

Twin and Adoption StudiesSeparated Twins

• U of MN studies on identical twins separated at birth – read book for variety of stories!

• Despite criticisms, the striking twin-study results helped shift scientific thinking toward a greater appreciation of genetic influences.

Twin and Adoption StudiesBiological Versus Adoptive Relatives

• Who contributes more genetic parents or adoptive parents?– People who grow up together

do not resemble one another in personality

– Environment does not have as much of an affect on children

Heritability• Heritability

–the extent to which variation among individuals can be attributed to their differing genes

–“difference among people”

–We can never say what percentage of an individual’s personality or intelligence is inherited.

• genetic influence explains 50 percent of the observed variation among people.

HeritabilityNature and Nurture

• Influence of adaptation- is our enormous adaptive capacity

• Nature and nurture work together –Our shared biology enables our

developed diversity

Gene-Environment Interaction• Genes and experience interact

–Evocative interactions– Environments trigger gene activity.– Children experience different parents,

depending on their own qualities– Our genes affect how people react to and

influence us. – Biological appearances have social

consequences.

The New Frontier: Molecular Genetics• Molecular genetics

–The goal of molecular behavior genetics is to find some of the many genes that influence normal human traits, such as body weight, sexual orientation, and extraversion, and also to explore the mechanisms that control gene expression

Natural Selection and Adaptation• Evolutionary psychology

– Natural selection– among the range of inherited trait variations,

those contributing to reproduction and survival will most likely be passed on to succeeding generations.

• Organisms‘ varied offspring compete for survival.• Certain biological and behavioral variations increase organisms‘

reproductive and survival chances in their particular environment.• Offspring that survive are more likely to pass their genes to

ensuing generations.• Thus, over time, population characteristics may change.

Evolutionary Success Helps Explain Similarities

• Behaviors that contribute to survival are found throughout cultures

• Our adaptive flexibility in responding to different environments contributes to our fitness—our ability to survive and reproduce.

Evolutionary Success Helps Explain Similarities

Outdated Tendencies

• Genetic traits which helped our ancestors survive may harm us today

Evolutionary Success Helps Explain Similarities

Evolutionary Psychology Today• Evolutionary psychologists have addressed questions such as these:

– Why do infants start to fear strangers about the time they become mobile?

– Why are biological fathers so much less likely than unrelated boyfriends to abuse and murder the children with whom they share a home?

– Why do so many more people have phobias about spiders, snakes, and heights than about more dangerous threats, such as guns and electricity?

– Why do humans share some universal moral ideas?– How are men and women alike? How and why do men‘s and

women‘s sexuality differ?

An Evolutionary Explanation of Human SexualityNatural Selection and Mating Preferences

• Differing preferences in partners–Male preferences

–Female preferences

Critiquing the Evolutionary Perspective

• Backward theorizing

• Impact of social influence

The End

Definition Slides

Behavior genetics

= the study of the relative power and limits of genetic and environmental influences on behavior.

Environment

= every non-genetic influence, from prenatal nutrition to the people and things around us.

Chromosomes

= threadlike structures made of DNA molecules that contain the genes.

DNA (deoxyribonucleic acid)

= a complex molecule containing the genetic information that makes up the chromosomes.

Genes

= the biochemical units of heredity that make up the chromosomes; segments of DNA capable of synthesizing a protein.

Genome

= the complete instructions for making an organism, consisting of all the genetic material in that organism’s chromosomes.

Identical Twins

= twins who develop from a single fertilized egg that splits in two, creating two genetically identical organisms.

Fraternal Twins

= twins who develop from separate fertilized eggs. They are genetically no closer than brothers and sisters, but they share a fetal environment.

Heritability

= the proportion of variation among individuals that we can attribute to genes. The heritability of a trait may vary, depending on the range of populations and environments studied.

Interaction

= the interplay that occurs when the effect of one factor (such as environment) depends on another factor (such as heredity).

Molecular Genetics

= the subfield of biology that studies the molecular structure and function of genes.

Evolutionary Psychology

= the study of the evolution of behavior and the mind,using principles of natural selection.

Natural Selection

= the principle that, among the range of inherited trait variations, those that lead to increased reproduction and survival will most likely be passed on to succeeding generations.

Mutation

= the random error in gene replication that leads to a change.