1. PowerPoint® Presentation by Jim Foley
Nature, Nurture,
And Human Diversity
PowerPoint® Presentation
by Jim Foley
© 2013 Worth Publishers

2. Module 11: Behavior Genetics and Evolutionary Psychology

3. 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
Temperament and Heredity
Molecular Genetics
Evolutionary Psychology: Adaptive Success
Example: Explaining Mating Preferences
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4. Behavior Genetics: Predicting Individual Differences
Behavior geneticists
study how heredity and environment contribute to human differences.
The topics in the text:
genes
twin and adoption studies
temperament and heredity
molecular genetics
heritability
gene/environment interaction
Let’s start by looking at GENES.
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Instructor: Behavior geneticists study how heredity and environment contribute to human differences. Following this slide is an optional slide in case you want that definition on screen. The book words it differently: “Behavior geneticists study our differences and weigh the interplay of heredity and environment.”
Using the word “predicting” here instead of “explaining” is a different standard as we assemble our evidence into theories. We hope to not only come up with descriptions that include reasons, but to understand patterns well enough that we can predict what will happen.
The focus in this section is on the tools we can use to explore the “nature” side of the equation; later we will look at cultural and other environmental influences on the brain, gender roles, and other traits and behaviors. We will wait until a later chapter to explore and possibly explain or predict individual and group differences in intelligence.

5. The Building Blocks of Heredity and Development
GENES:
The Building Blocks of Heredity and Development
Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells.
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DNA
(Deoxyribonucleic Acid)

6. Chromosomes are made of DNA, which are made of genes.
Chromosome: threadlike structure made largely of DNA molecules
DNA:
a spiraling, complex molecule containing genes
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7. 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.
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8. The Human Genome: 20,000 to 25,000 Genes
The genome: an organism’s entire collection of 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.
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9. 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.
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Note: there is rarely one single gene for one trait, and tiny differences in genes can influence big differences in appearance and behavior.

10. Next step for behavior geneticists: Controlling Variables
Can we design an experiment to keep genes constant and vary the environment and see what happens?
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Answer to these questions:
Not exactly, but we can observe what has happened when those circumstances have arisen, such as in twin and adoption studies.
Or vary the genes in the same environment?

11. Fraternal and Identical Twins
Twin and Adoption Studies
To 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 “twins” from separate eggs are not any more genetically alike than other siblings.
Identical twin: Same sex only
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Fraternal twins are more alike than other siblings, however, in the home environment they share. They are raised at the same time in their parents’ lives, with the same number and age of siblings.
Even identical twins, though, can have biological differences, if they have separate placentas (this happens in about one out of three times) and thus get different nourishment.
Fraternal twin: Same or opposite sex

12. Identical vs. Fraternal Twins
Twin and Adoption Studies
How 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).
Studies 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.
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Instructor: In these and related studies, not only are identical twins more alike than fraternal twins, but fraternal twins are more alike than random strangers even though random strangers are also raised in different environments.
Question for the students, in this slide and the next: which factor is being controlled here, and which factor is varying? [Answer: presumably, these studies are done on twins raised at first together, then having some adult time apart; if fraternal twins have more differences than identical twins, the only factor which has varied is the level of genetic similarity.]

13. Studies of Identical Twins Raised Apart
Critiques of Twin Studies
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.
Coincidences happen; some randomly chosen pairs of people will have similar traits, including even spouses, children, and dogs with identical names.
Environments may be similar; adoptive families tend to be more similar than randomly selected families in education, income, and values.
Similarities 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 rate
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Instructor: There are cases in which identical twins are separated at birth through adoption but are later found to be twins. The Minnesota Twin Family Study is the biggest example of this.
Again, I suggest asking the students: which factor is being controlled here, and which factor is varying?
Sidebar: Another critique is that the environments or “nurture” may be more similar for twins than for a pair of unrelated people because they look identical and thus are treated more similarly.
BUT none of these factors explains, better than the genetic explanation, why fraternal twins have more differences than identical twins.

14. Searching for Parenting Effects: Biological vs. Adoptive Relatives
Studies 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?
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15. Parenting Does Matter religious beliefs values manners attitudes
Despite the strong impact of genetics on personality, parenting has an influence on:
religious beliefs
values
manners
attitudes
politics
habits
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16. If parenting has an influence, why are siblings so different?
Siblings only share half their genes.
Genetic differences become amplified as people react to them differently.
Siblings are raised in slightly different families; the youngest has more older siblings and has older (wiser? more tired?) parents.
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17. Temperament is another difference not caused by parenting.
From infancy into adulthood, most people do not seem to change temperament (defined as a person’s general level and style of emotional reactivity).
According to some researchers, three general types of temperament appear in infancy:
“easy”
“difficult”
“slow to warm up”
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Biological explanations: anxious, inhibited infants have fast and variable heart rates and a reactive nervous system
Experience matters too. Supportive parenting can reduce the impact of early withdrawal, and unsupportive parenting or trauma can bring out the anxious, inhibited personality in a child who is predisposed to this temperament.

18. Molecular Genetics Click to reveal bullets.
Molecular genetics is the study of the molecular structure and function of genes.
Molecular genetics might help us see exactly how specific genes have an influence on behavior.
Genetic tests can reveal which people are at risk for many physical diseases, and may soon identify people at risk of mental health disorders.
Ethical conundrum: should people use genetic tests to select sperm, eggs, and even embryos?
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19. Clarifying Heritability
If five unrelated people had nearly identical upbringing, but differed in a trait such as shyness, then the heritability of this trait for them is close to 100 percent.
Nurture may have influenced how shy they are, but because it influenced them all in the same way, any differences are almost certainly caused by genes.
When you see a variation of some trait within a population, the heritability of that trait is the amount of variation in the population that is explained by genetic factors.
This DOES NOT tell us the proportion that genes contribute to the trait for any one person.
The heritability of a trait also does not tell us whether genetics explain differences between groups/populations.
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Height is 90 percent heritable in general. However, as a group, people are taller in this century than last, or in South Korea compared to North Korea. This is probably not caused by genetics but by nurture (nutrition).
Sidebar: This explanation is also presented in the slides for the chapter on intelligence. You may want to delete it in one of the two places.

20. How does the interaction of genes and environment work?
Nature and nurture working together Interaction of Genes and Environment
Some traits, such as the overall design of our bodies, are set by genes.
Other traits, such as physical and mental abilities, develop in response to experience.
How does the interaction of genes and environment work?
Genetic traits influence the social environment, which in turn affects behavior.
Click to reveal bullets and example.
Example: the levels above genes on the slide. Someone predisposed to depression may have that predisposition triggered by chronic stress or hormonal changes. These can lead to lifestyle changes which can reinforce depression, even changing activity in the brain. Some environmental influences can turn genes on and off.
The chart, summarizing the mutual influences among genes, brain, behavior, and environment, is from at least one article by Gilbert Gottlieb, found at:
Gilbert Gottlieb also has written more recently about epigenesis.

21. How does the interaction of genes and environment work?
Example of self-regulation in animals: shortened daylight triggers animals to change fur color or to hibernate
Self-regulation: genes turn each other on and off in response to environmental conditions
Epigenetics: the environment acts on the surface of genes to alter their activity
Example of self-regulation in humans:
obesity in adults can turn off weight regulation genes in offspring
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The main mechanism for epigenetic change is the methyl molecule on DNA which essential deactivates it, keeping the gene from coding proteins.
Sample of some of the citations on the obesity result at the bottom:

22. The Human Approach to Nature and Nurture
The trait of being adaptable is built into the human genome.
Paradox: our genes allow us not to be tied so much to our genes!
We have minds which allow us to change our behavior in response to the environment to a greater degree than other species.
We even shape our environments to suit our nature.
Humans can adapt to a variety of climates, diets, lifestyles, and skills.
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Part of our universal human biological heritage is our ability to use that heritage in a great variety of ways.
Some species have a biological ability to adapt by changing colors with the seasons; humans have the ability to adapt to a variety of climates, diets, lifestyles, and skills.

23. Evolutionary Psychology:
Understanding Human Nature
Some topics:
Natural selection and adaptation
Evolutionary success may help explain similarities
An evolutionary explanation of human sexuality
Evolutionary psychology is the study of how evolutionary principles help explain the origin and function of the human mind, traits, and behaviors.
Click to reveal definition of evolutionary psychology.
Evolutionary principles are used in evolutionary psychology to explain human universals and commonalities; qualities that helped ancestors survive and reproduce and spread those traits in the genes of many offspring.
We have been talking so far about human differences; we may now seek insight in the ways in which humans are alike.

24. Natural Selection: How it Works
Evolutionary Psychology:
Natural Selection: How it Works
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.
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25. Artificial Selection The Domesticated Silver Foxes
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.
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26. How might evolution have shaped the human species?
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.
Possible explanation: 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 cling to parents around the time they learned to walk.
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Another possible example of evolutionary shaping (from the text): the instinct to dislike bitter foods (which may have been toxic to our ancestors) especially during pregnancy.
Critique of evolutionary psychology: it begins with an effect (stranger anxiety, phobias) and works backward to propose an explanation. It is almost impossible to lose when proposing an explanation in hindsight, and these explanations almost always defy the level of scientific scrutiny and verification suggested in Chapter 1.

27. Evolutionary Psychology’s Explanation of Phobias
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 and reproduce.
Can we apply the same logic to phobias about heights? enclosed spaces? clowns?
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Discussion question: why are clowns such a common phobia? Hint at a possibility: there is evidence that our lineage split away from those that evolved into today’s baboons and mandrills long before our ancestry diverged from today’s chimpanzees or even gorillas and orangutans. Check out a picture of a mandrill…
Critique: note how once an evolutionary psychologist has the effect (clown phobia), almost any proposal can be suggested to explain it. This is why noted paleontologist Stephen Jay Gould (1997) called hindsight explanation nothing more than “speculation [and] guesswork in the cocktail party mode.”
Note: spiders were removed from this example because they are rarely poisonous and are far less dangerous than many other animals.

28. A Possible Human Genetic Legacy: “Illogical” Moral Reasoning
It might be “logical” to kill one innocent person if it would enable five other innocent people to live. Research shows that most people can imagine letting the one person die, but cannot picture killing the person themselves.
Why would it be instinctual not to kill unless we are directly threatened?
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This scenario of killing one person to save many (vs. LETTING someone die to save many) has been presented in many forms. The one in the text about pushing someone into a vent, and the classic train or trolley example, presented as pulling a switch or pushing someone off a bridge to divert a train or slow a trolley to save others on the tracks.
There is no agreed-upon correct answer to the question on the slide. However, you might want to ask, "why risk our lives trying to kill someone unless it was to prevent our own death or the death of those who share our genes? (It would be interesting to test people on these scenarios, but this time, picture your family in danger and a stranger who must be killed.)

29. Male and Female Differences: Focusing on Mating Preferences
First issue: quantity (of mating)
Generally, men think more than women about sex, and men are more likely to think that casual sex is acceptable.
Why might natural selection have resulted in greater male promiscuity?
An evolutionary psychologist’s answer:
Click to reveal bullets, question and answers.
Instructor: more about other male/female differences, ones which are presumed to be more influenced by culture than genes, later in the chapter.
The information below is for your use in case you decide not to use upcoming 2-3 slides to save time:
The potential answer to this question that I hope students can figure out: males who had the trait of promiscuity are more likely to have their genes continue, even spread, in the next generation. And there is little cost to spreading extra genes.
Promiscuous women, by contrast, might have been LESS likely to have this result, because they would be less likely to have stable male partners around to help with the parenting than women who were more selective about whom they had sex with.
Men who had the trait of promiscuity were more likely to have their genes continue, and even spread, in the next generation. And there is little cost to spreading extra genes.
For women, a trait of promiscuity would not greatly increase the number of babies, and it would have greater survival costs (pregnancy, once a life-threatening condition).

30. Possible Evolutionary Strategies in Seeking Partners
Q: How would evolutionary psychology explain why males and females have different preferences for sexual partners?
Men seek women with a fuller figure… to make sure they are not too young or too old to have children? Women seek males with loyal behavior and physical/social power and resources… in order to ensure the survival of the mother’s offspring?
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31. Critiquing the Evolutionary Perspective on Gender Differences in Sexuality
Are males and female really so different in their mating choices?
Differences are less in cultures that move to gender equality.
Isn’t much of gender behavior a function of culture?
Yes, as we’ll see later in this lesson.
How do you explain homosexuality?
Guesses such as population control or misplaced instincts are unproven and seem forced.
Click to add notes.
Does evolutionary psychology really tell us anything useful?
See next slide…

32. 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.”
Click to show two critiques and responses.
Instructor: You can ask students to explain why people all over the world like soccer based on an evolutionary psychology perspective. Students can invent great explanations…because our distant ancestors had to kick stones out of the way; because people who kicked lions really hard survived to spread their genes…etc.)
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.”