Objective: 10/20/15Provided notes, SWBAT evaluate how evolved tendencies influence behavior, and describe the interactive effects of heredity & the environment.

Agenda:1. Do Now2. Notes-genetics3. Project

Biological Behavior, Heredity, & Evolutionary Psychology

“We have found the most interesting

universe, & it is us.” - David Eagleman

Heredity & Behavior: Is It All in the Genes?

Do Now: In your groups discuss and answer the following question.

Do genetic or environmental factors have a greater influence on your behavior? Do inherited traits or life experiences play a greater role in shaping your personality?

Heredity & Behavior: Is It All in the Genes?Physical characteristics such as height, hair color, blood type, & eye color are largely shaped by heredity. What about psychological characteristics, such as intelligence, moodiness, impulsiveness, & shyness?

To what extent are people’s behavioral qualities molded by their genes?

Behavioral Genetics: An interdisciplinary field that studies the influence of genetic factors on behavioral traits.Field has grown by leaps & bounds since the 1970s, & this research has shed new light on the age-old nature versus nurture debate.

Basic Principles of GeneticsEvery cell in your body contains enduring messagesfrom your mother & father. These messages arefound on the chromosomes that lie within the nucleus of each cell.Chromosomes: Strands of DNA (deoxyribonucleic acid) molecules that carry genetic informationZygote: A single cell formed by the union of a sperm & an egg.A single pair of parents can produce an extraordinary variety of combinations of chromosomes.

Each parent’s 23 chromosome pairs can be scrambled in over 8 million different ways, yielding roughly 70 trillion possible configurations when sperm & egg unite. Everything is a matter of probability. Except for identical twins, each person ends up with a unique genetic blueprint.

Sex Characteristics - Primary/Secondary

Primary & secondary sexual characteristics refer to specific physical traits that differentiate males & females in sexually dimorphic species; that is, species in which males & females look different. Primary sexual characteristics are there from birthSecondary sexual characteristics emerge at puberty (such as low voices & beards in men, & high voices & no facial hair in women)

Which parent decides whether a baby will be a boy or a girl?In humans & many other species of animals, the father determines the sex of the child.

Neither parent gets to decide. Almost everyone has around a 50% chance of having a boy & a 50% chance of having a girl.

What we can say is that dad's sperm determines whether a baby will be a boy or a girl. About 1/2 of his sperm will make a boy & half a girl. The sex of the baby depends on which sperm gets to the egg first.

In the XY sex-determination system, the female-provided ovum contributes an X chromosome & the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively.

Hormone levels in the male parent affect the sex ratio of sperm in humans. Maternal influences also impact which sperm are more likely to achieve conception.

HOMOZYGOUS HETEROZYGOUS

Homozygous & Heterozygous genotypes.

Like chromosomes, genes operate in pairs, with one gene in each pair coming from each parent.

Whether people have attached or detached earlobes is determined by a single pair of genes.

In the heterozygous condition, genes for detached earlobes are dominant over genes for attached earlobes.

Basic Principles of GeneticsLike chromosomes, genes operate in pairs, withone gene of each pair coming from each parent.

Homozygous condition: The two genes in a specific pair are the same.

Heterozygous condition: The two genes in a specific pair are different.

When the parents contribute genes for different types of earlobes (the heterozygous condition), one gene in the pair—called the dominant gene—overrides or masks the other, called the recessive gene.

Dominant Gene: One that is expressed when paired genes are different.

Recessive Gene: One that is masked when paired genes are different.

Dominant & Recessive Genes

A dominant gene is expressed no matter what.

A recessive gene can only be displayed if BOTH the genes received from the parents are the same recessive gene. Think of it this way: A dominant gene is like the sun & recessive genes are like the stars. If the sun is in the sky the stars cannot be seen even though they are there. Likewise, when a dominant gene is present the recessive genes are all hidden. But if there are no dominant genes around we can see recessive genes. In humans, the gene for brown eyes is dominant & the gene for blue eyes is recessive. So if we received one brown gene from dad & one blue gene from mom only the brown gene would be expressed. Our eyes would be brown (Image 1).

Basic Principles of GeneticsBecause genes operate in pairs, a child has a 50%probability of inheriting a specific gene in a particular gene pair from each parent.

Ranges from 100% for identical twins down to 6.25% for second cousins

Genotype: A person’s genetic makeup. Phenotype: Refers to the ways in which a person’s genotype is manifested in observable characteristics.

Genotype is determined at conception & is fixed forever. In contrast, phenotypic characteristics (hair color, for instance) may change over time. They may also be modified by environmental factors. Most human characteristics appear to be polygenic traits, or characteristics that are influenced by more than one pair of genes.

3 to 5 gene pairs are thought to determine skin color.

Identical vs. FraternalIdentical (monozygotic) twins emerge from one zygote that splits, so their genetic relatedness is 100%.

Identical vs. FraternalFraternal (dizygotic) twins emerge from two separate zygotes, so their genetic relatedness is only 50%.

Higher correlations found for identical twins indicate that they tend to be more similar to each other than fraternal twins on measures of general intelligence & measures of specific personality traits, such as extraversion.

However, the fact that identical twins are far from identical in intelligence & personality also shows that environment influences these characteristics.

Identical twins tend to be more similar than fraternal twins (as reflected in higher correlations) with regard to intelligence & specific personality traits, such as extraversion. Fndings suggest that intelligence & personality are influenced by heredity.

Basic Principles of Genetics

Epigenetics: Study of heritable changes in gene expression that do not involve modifications to the DNA sequence. Specific genes’ effects can be dampened or silenced by chemical events at the cellular level, leading to phenotypic alterations in traits, health, & behavior.

David Eagleman: Brain Over Mind

Evolutionary PsychologyEvolutionary Psychology: The study of how evolutionary principles help explain the origin & function of the human mind, traits, & behaviors.

★ Natural selection & adaptation★ Evolutionary success may help explain

similarities★ An evolutionary explanation of human

sexuality

Why do people so easily acquire a phobia of snakes?

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

Can we apply the same logic to phobias about heights? Enclosed spaces? Clowns?

“Can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and procreating their kind? . .This preservation of favourable variations and the rejection of injurious variations, I call Natural Selection.”- Charles Darwin

Principle of Natural Selection:Heritable characteristics that provide a survival or reproductive advantage are more likely than alternative characteristics to be passed on to subsequent generations and thus come to be “selected” over time. Please note: The process of natural selection works on populations rather than individual organisms. Evolution occurs when the gene pool in a population changes gradually as a result of selection pressures. This process tends to be extremely gradual. It generally takes thousands to millions of generations for one trait to be selected over another.

Khan Academy: Intro to Evolution & Natural Selection