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The Biology of Behavior
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 Interaction Evolutionary Psychology: Adaptive Success Artificial and Natural Selection Critiques of Evolutionary Thinking
Behavior Genetics: Predicting Individual Differences
Behavior geneticists study how heredity and environment contribute to human differences. More ways of exploring the origins of the biology of behavior: Understanding genes Twin and adoption studies Gene/environment interactions Evolutionary Psychology Let’s start by looking at GENES. Click to show Behavior geneticists box. 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.
The Building Blocks of Heredity and Development GENES:
Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells. Genes are parts of DNA molecules, which are found in chromosomes in the nuclei of cells. No animation. DNA (Deoxyribonucleic Acid)
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 Automatic animation. }
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. Click to reveal bullets.
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. Click to reveal bullets.
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. Click to reveal bullets. Note: there is rarely one single gene for one trait, and tiny differences in genes can influence big differences in appearance and behavior.
Next step for behavior geneticists: Controlling Variables
Can we design an experiment to keep genes constant and vary the environment and see what happens? Automatic animation. 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?
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 Click to reveal sidebar. 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
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. Click to reveal sidebar. 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.]
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. 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 Click to reveal bullets, then more in sidebar. 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.
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? Click to reveal bullets.
Parenting Does Matter Despite the strong impact of genetics on personality, parenting has an influence on: religious beliefs values manners attitudes politics habits Automatic animation.
How does the interaction of genes and environment work?
Example in animals: shortened daylight triggers animals to change fur color or to hibernate 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 Example in humans: obesity in adults can turn off weight regulation genes in offspring Click to reveal bullets and examples. 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:
Understanding Human Nature Some topics: Natural selection and adaptation Evolutionary success may help explain similarities 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; let’s now seek insight into the ways in which humans are alike.
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. Automatic animation.
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. Click to reveal bullets.
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. 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. Click to reveal bullets. Optional Slide. 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.
Evolutionary Psychology’s Explanation of Biologically Driven Phobias
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. Click to reveal bullets. Optional Slide. 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.
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.”
Evolution: Theory 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. 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? Click to reveal bullets and sidebar bullets.
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