PowerPoint®Presentation by Jim Foley

The Biology of Behavior

© 2013 Worth Publishers

Module 5: Genetics, Evolutionary Psychology, and Behavior

Topics we were born to learn about

Behavior Genetics and Individual Differences Genes: Molecules that code for life Learning about heredity from Twin and

Adoption Studies Gene-Environment InteractionEvolutionary Psychology: Adaptive Success Artificial and Natural Selection Critiques of Evolutionary Thinking

Behavior Genetics: Predicting Individual Differences

More ways of exploring the origins of the biology of behavior:1. Understanding genes 2. Twin and adoption

studies 3. Gene/environment

interactions4. Evolutionary

Psychology

Behavior geneticists

study how heredity and environment

contribute to human differences.

Let’s start by looking at GENES.

Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells.

DNA (Deoxyribonucleic Acid)

GENES:The Building Blocks of Heredity and Development

Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells.

GENES:The Building Blocks of Heredity and Development

Chromosomes are made of DNA, which are made of genes.

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Chromosome: threadlike structure made largely of DNA

molecules

DNA: a spiraling, complex molecule containing

genes

Chromosomes and Inheritance The human genome includes 46

chromosomes in 23 sets matched sets; each chromosome has the same gene locations.

This includes the X and Y chromosomes, not a matched set in males, who are missing some genes on the Y.

A biological parent donates half his/her set of chromosomes to his/her offspring.

We received half a set of chromosomes from each biological parent.

The Human Genome:20,000 to 25,000 Genes Human genomes are so nearly

identical that we can speak of one universal human genome.

Yet tiny genetic differences make a difference. If there is a: .001 percent difference in

genome, your DNA would not match the crime scene/you are not the baby’s father.

0.5 to 4 percent difference in genome, you may be a chimpanzee.

50 percent difference in genome, you may be a banana.

The genome: an organism’s entire

collection of genes

How Genes Work Genes are not blueprints;

they are molecules. These molecules have

the ability to direct the assembly of proteins that build the body.

This genetic protein assembly can be turned on and off by the environment, or by other genes.

Any trait we see is a result of the complex interactions of many genes and countless other molecules.

Or vary the genes in the same environment?

Next step for behavior geneticists:Controlling Variables

Can we design an experiment to keep genes

constant and vary the environment and see what

happens?

Twin and Adoption StudiesTo assess the impact of nature and nurture, how do we examine how genes make a difference within the same environment? study traits of

siblings vs. identical twins

see if the siblings vary more than twins

Fraternal and Identical Twins

Fraternal “twins” from separate eggs are not any more genetically alike than other siblings.

Identical twin: Same sex only

Fraternal twin: Same or opposite sex

Twin and Adoption StudiesHow do we find out how the same genes express themselves in different environments?We can study the traits of identical twins as they grow up, or if they were raised separately (e.g., the Minnesota Twin Family Study).

Identical vs. Fraternal TwinsStudies of twins in adulthood show that identical twins are more alike than fraternal twins in: personality traits such as

extraversion (sociability) and neuroticism (emotional instability).

behaviors/outcomes such as the rate of divorce.

abilities such as overall Intelligence test scores.

Critiques of Twin Studies1. In the more recent years of the

Minnesota Twin Family Study, twins have known about each other and may influence each other to be more similar.

2. Coincidences happen; some randomly chosen pairs of people will have similar traits.

3. Environments may be similar; adoptive families tend to be more similar than randomly selected families in education, income, and values.

Studies of Identical Twins Raised ApartSimilarities found in identical twins despite being raised in different homes: personality, styles of

thinking and relating abilities/intelligence

test scores attitudes interests, tastes specific fears brain waves, heart

rateBUT none of these factors explains, better than the genetic explanation, why fraternal twins have more differences than identical twins.

Searching for Parenting Effects:Biological vs. Adoptive RelativesStudies have been performed with adopted children for whom the biological relatives are known.Findings: Adopted children seem to be more similar to their genetic relatives than their environmental/nurture relatives.

Given the evidence of genetic impact on how a person turns out,

does parenting/nurture make any difference?

Does the home environment have any impact?

Despite the strong impact of genetics on personality, parenting has an influence on:

religious beliefs values manners attitudes politics habits

Parenting Does Matter

Gene-Environment Interaction: genes turn each other on and off in response to environmental conditions

Epigenetics: The study of how this happens: The environment acts on the surface of genes to alter their activity

How does the interaction of genes and environment work?

Example in animals: shortened daylight triggers animals to change fur color or to hibernate

Example in humans: obesity in adults can turn off weight regulation genes in offspring

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Some topics: Natural selection and

adaptation Evolutionary success may help

explain similarities

Evolutionary Psychology: Understanding Human Nature

Evolutionary psychology is the

study of how evolutionary

principles help explain the origin and

function of the human mind, traits, and

behaviors.

We have been talking so far about human differences; let’s now seek insight into the ways in which humans are alike.

Begin with a species’ genome, which contains a

variety of versions of genes that shape traits.

Conditions make it difficult for

individuals with some traits (some versions of those genes) to survive long enough to

reproduce.

Other individuals thus have their

traits and genes “selected” to spread in the population.

Evolutionary Psychology: Natural Selection: How it Works

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Dmitri Balyaev and Lyudmila Trut spent 40 years selecting the most gentle, friendly, and tame foxes from a fox population, and having those reproduce.

As a result, they were able to shape avoidant and aggressive creatures into social ones, just as wolves were once shaped into dogs.

Artificial SelectionThe Domesticated Silver Foxes

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Example: Why does “stranger anxiety”

develop between the ages of 9 and 13 months? Hint: in evolutionary/survival terms, humans are learning to walk at that time.Infants who used their new ability to walk by walking away from family and toward a lion might not have survived to reproduce as well as those who decided to stay with parents around the time they learned to walk.

How might evolution have shaped the human species?

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Why do people so easily acquire a phobia of snakes, more easily than a phobia of cars?

An evolutionary psychologist would note that snakes are often poisonous……so, those who more readily learned to fear them were more likely to survive and reproduce.

Evolutionary Psychology’s Explanation of Biologically Driven Phobias

Critiquing Evolutionary Psychology

“You’re just taking current

reality and constructing a way you could have predicted

it.” This is hindsight

reasoning and unscientific.

“You’re attributing too much to genes rather than the

human ability to make choices about social behavior.”

Response: yes, but there are predictions made about future behavior using this reasoning.

Response: yes, but our evolutionary past does not prevent our ability to act differently; “is” does not equal “ought.”

Evolution: Theory Evolution is a scientific theory

(NOT a “guess” and not a hypothesis, but something more): a coherent set of principles that fits very well with the accumulated evidence.

Parts of the evolutionary story may conflict with other stories of origins and change over time.

Is there room for overlap and agreement?

Possible areas of consensus, with or without evolution: The human mind

and body seems almost “designed,” by evolution or other forces, to have certain traits and abilities.

Nurture may shape us, but we seem to start out with some sort of human nature.