GENETICS, EVOLUTIONARY PSYCHOLOGY

Genes, twin studies, heritability, Nature vs. Nurture

Genes Chromosomes: threadlike structures made of DNA

molecules that contain genes Humans normally have 46 chromosomes, 23 from the

mother and 23 from the father. Each chromosome is a coil of DNA (deoxyribonucleic acid) The DNA contain small segments called genes Humans have approximately 30,000 genes Genes can be active (expressed) or inactive Genes can be turned on by environmental triggers, which

causes the gene to express The genome contains all the genetic material in an

organisms chromosomes, in essence, the instructions for making that organism

Twins To understand the influence of heredity

and environment, researchers would need to create scenarios that either vary the environment but not the heredity or vary the heredity but not the environment.

It would be unethical to create these scenarios, but nature has provided them.

Twins Identical twins Formed from a

fertilized egg that splits

monozygotic Genetically

identical Also share same

prenatal circumstances and same cultural history

Fraternal twins develop from two

separate eggs fertilized at the same time

dizygotic Share some

prenatal circumstances

twins Identical twins have the

same genes but do not always have the same number of copies of those genes (can explain why one identical twin is more likely to have a disease)

Most share a placenta but not all, could lead to differences due to prenatal nutrition

Mirror twins: mirror images of each other example: one right handed and the other one left handed

May have different personalities and interests, show that heritability of a trait doesn’t mean it will occur even in two people who share the same genes

StudiesThere are and have been several twin studies

worldwideStudies have shown that:1) Identical twins are more similar than fraternal

twins in both extraversion and neuroticism2) Disease risks are increased for identical twins3) Divorce risk (by examining rates) are about

50% attributable to genetics4) Similar treatment does not predict

psychological behavior, in behavior genes matter

Studies Minnesota twin: Thomas Bouchard Matt McGue and David Lykken (1992) John Loehlin and Robert Nichols (1976) Nancy Pederson(1988)

Twin Studies Although, in studies by Pederson,

identical twins separated at birth had less identical personalities than identical twins raised together, they were more alike than fraternal twins separated at birth.

Critics often point out that coincidences happen and they we often share characteristics with our age peers regardless of genetics

Adoptive relatives Adoption creates two family groups: genetic

relatives and environmental relatives One finding from studying adoptive families, is

that people who grow up together do not much resemble each other in personality, regardless of biology(McGue & Bouchard,1998)

In extraversion and agreeableness, adoptive children resemble their biological parents more than their adoptive parents

Environment seems to have no discernible impact on personality development

Adoptive family research Why this is so and the impact of it fuels

further research into the topic Adoptive environments do influence

values, attitudes, manners and faith/politics

So while genetics dominates personality development, environment influences other facets of the person

Adoptive families are often less likely to experience child abuse , neglect and even divorce

Adoptive family research In one study, (Bohman & Sigvardsson,

1990) children who were adopted had fewer problems than children who were registered for adoption but the mother changed her mind

Even though at a greater risk for psychological disorder, most adoptive children thrive ( Loehlin, 2007)

Many score higher on IQ tests than their biological parents and have more stable lives

Assignment Thinking about this information, the

Pinker TED talk and your own input/experience

Address the following quotes:1) “We carry to our graves the essence of

the zygote that was first us.”2) “The plural of anecdote is not data.”

Heritability Heritability is the proportion of variation

among individuals that we can attribute to genes.

Heritability may vary based on the range of populations and environments studied

Adoption and twin studies have been used by behavior geneticists to determine the heritability of a trait—the extent to which variation among individuals can be attributed to their differing genes

Heritability For example: if intelligence is determined to

have a 50% heritability, this does not mean that 50% of your intelligence is genetic or inherited. It means that genetic influence explains 50% of the variation in people’s intelligence.

If environments were exactly the same, heritability would rise; in situations where environments are similar, heritability as a source becomes more significant; if environments were less similar but genetics were more similar, heritability would be lower.

Group differences Individual differences and group

differences cannot be explained in the same way.

For example: height and weight in individuals are highly heritable ,but that will not explain why we are taller and heavier today than our ancestors. That is explained by nutritional/environmental reasons not genetic ones.

Nature vs. Nurture Genes and environment work together. Genes code for

particular proteins but also respond to the environment. Genes are self-regulating and adaptive. For example; a

butterfly that is green in the summer turns brown in the fall. The genes that produce the green coloring also produce the brown coloring triggered by environment and a temperature controlled genetic switch.

The genes react, instead of following a non-changing blueprint.

This is why people with identical genes but differing environment/experiences will often have similar but not identical minds.

Gene-environment interaction

Genes and environment are both important and interact with each other.

Think more nature via nurture not nature vs. nurture For example; 2 babies born, one with the

predisposition to be attractive, sociable and easygoing the other less so. If the baby that is predisposed receives more positive attention and stimulation it will grow into a more outgoing and confident person. As a more confident person, the child will seek activities that further encourage social confidence.

The differences in the children’s personalities is caused by the dance between genes and environment.

Molecular genetics

A study of genes from the molecule up, to determine which specific genes influence behavior.

The goal is to identify some of the genes that influence certain traits and to explore the mechanisms that control gene expression.

Molecular geneticists are working on pinpointing genes that can cause a wide array of psychologically connected issues, such as: alcoholism, bipolar disorder, depression, and learning disorders.

Evolutionary Psychology Evolutionary psychologists use Darwin’s principle

of natural selection to study the roots of human behavior and mental processes.

1) Organisms’ varied offspring compete for survival

2) Certain biological and behavioral variations increase organisms’ reproductive and survival chances in a particular environment

3) offspring that survive are more likely to pass their genes to future generations

4) Thus, over time, population characteristics may change

Does natural selection explain human tendencies?

While nature has selected advantageous variations from genetic mutations and from gene combinations produced at conception, humans genetic leash is looser than that of animals. Our genes selected over years allow us to adapt to a variety of environments and to learn. Genes and experience together wire our brains. Our ability to adapt and be flexible in responding to different environments adds to our fitness—the ability to survive and reproduce.

Assignment Read page 104: Evolutionary success

helps explain similarities and paraphrase the main concepts/ideas

Read page 107: Critiquing the evolutionary perspective and paraphrase the main concepts/ideas

Read pages 108-110: After reading “Reflections on Nature and Nurture”, write about it. What do you think? Did the passage trigger any thoughts, feelings? If so, what are they?