chapter 3 Genetic and Evolutionary Foundations of Behavior

Transcription

1 Genetic and Evolutionary Foundations of Behavior chapter 3 READ the introduction below before you read the chapter in the text. Chapter 3 focuses on the impact of genetics and evolutionary adaptation on behavior. Adaptation is a means of accommodating to changed circumstances. (Evolution is just one level on which adaptation occurs; another is learning, which will be considered in Chapter 4.) Genes, the biological units of heredity, affect our anatomy and physiology and, through these, affect our behavioral characteristics. They have their effects solely by governing the manufacture of the body s many different protein molecules. Genes always work in interaction with environmental influences. This chapter explains how genetic information is passed down from one generation to the next through sexual reproduction. Such concepts as genetic diversity, genotypes and phenotypes, and dominant and recessive genes are explained. In some cases, a single gene can affect a particular aspect of behavior or cause genetic disorders that have behavioral consequences. But most differences among individuals stem from the combined effects of many genes in interaction with the environment. We call these polygenic characteristics. Polygenic characteristics vary in degree from one individual to another that is, each individual will have more or less of the characteristic. In contrast, in the case of single-gene differences, individuals differ in type rather than degree. The mechanism by which evolutionary adaptation takes place is natural selection, a concept originated by Charles Darwin. Darwin argued that inheritable changes that enhance the chances of survival and reproduction tend to be passed on to the next generation while inheritable changes that hinder survival or reproductive chances are lost. In other words, those genes that thwart survival or reproduction are less likely to be passed on to future generations and thus become rarer or disappear. In current evolutionary thinking, Darwin s critical insights are combined with a modern understanding of genes. People have long engaged in selective breeding reproducing plants and animals in such a way that desirable traits are developed, enhanced, or continued. Evolution depends on natural selection, defined above, in which the demands of life in a particular environment determine what is a desirable trait. Genetic diversity provides the raw material for natural selection, but environmental change propels the process. It is important to recognize that evolution does not involve foresight, since common misconceptions about evolution stem from this erroneous assumption. Functionalism, which emphasizes the purposes of behavior, is well suited to an evolutionary viewpoint. However, not all characteristics that emerge through evolution should be assumed to be useful. The chapter next explores instinctual or speciestypical behaviors, such as speaking in humans or dam-building in beavers. Although biological preparedness is the foundation for such behaviors, learning can be involved in even critical to their development. Cross-species comparisons of speciestypical behaviors are enlightening. Two types of comparisons homology and analogy are used in trying to understand the evolutionary development and functions of behaviors. One major focus of the evolutionary perspective has been sexual behavior. Robert Trivers, for example, has suggested that the relative parental investments required of males and females of a given species will strongly affect the mating patterns seen in that species. Thinking in evolutionary terms has also helped us understand aggression, including the greater aggressiveness of male primates as compared with females of their species. Helping behavior in humans and other species can be explained as consistent with natural selection, as well. The chapter also describes fallacies in evolutionary thinking that we should avoid. 25

2 26 Chapter 3 Genetic and Evolutionary Foundations of Behavior Notice that there are focus questions in the margins of the text for your use in studying the material. The following chart lists which Study Guide questions relate to which focus questions. Focus Questions Study Guide Questions Review of Basic Genetic Mechanisms Inheritance of Behavioral Traits Evolution by Natural Selection Natural Selection as a Foundation for Functionalism Natural Selection as a Foundation for Understanding Species-Typical Behaviors Evolutionary Analyses of Mating Patterns Evolutionary Analyses of Hunting and Helping The Integrated Study Workout COMPLETE one section at a time. Introduction AND Review of Basic Genetic Mechanisms (pages 51 57) CONSIDER these questions before you go on. They are designed to help you start thinking about this subject, not to test your knowledge. How can a microscopic physical thing like a gene affect something psychological such as verbal ability? How are genes passed down from parents to children? How is the environment related to genetic influences on behavior? READ this section of your text lightly. Then go back and read thoroughly, completing the Workout as you proceed. In the mid-nineteenth century, Charles Darwin offered a theory of evolution that explained the basis for both similarities and differences among animal species. Evolution is a long-term adaptive process. 1. Define adaptation. Amazingly, Darwin s theory preceded our understanding of genes but a knowledge of genes adds immeasurably to our understanding of evolution. Genes are the basic building blocks of heredity. If we want to understand the genetic contribution and evolutionary forces that shape behavior, we must understand how genes exert their effects and how they are transmitted from one generation to the next. 2. Do genes affect behavior directly? Explain. 3. Genes affect physical development by directing the synthesis of molecules. The structure of every cell in the body is made

3 Chapter 3 Genetic and Evolutionary Foundations of Behavior 27 up of proteins called proteins, and control the rate of chemical reactions in the cells. Each protein molecule consists of a sequence of hundreds or thousands of (of which there are distinct varieties). Physically, genes are segments of long molecules of. 4. Define each of the following. a. genes (Hint: Provide an older and a newer definition.) 6. How are genes thought to play a part in long-term behavioral changes resulting from experience? Give a specific example. 7. The same genotype can produce different phenotypes. individual inherits The set of genes that the The observable properties of the body and behavioral traits. b. coding genes It is useful to understand how genetic material is passed down from parents to offspring in sexual reproduction. 8. Strands of DNA are arranged in each cell in structures called. c. regulatory genes 9. How many pairs of chromosomes are in a normal human cell (except an egg or sperm cell)? d. junk DNA 10. One pair of chromosomes are sex chromosomes. How do the sex chromosomes of males and females differ? It is very important to understand that the effects of genes are always interwoven with the effects of the environment. Neither one alone can affect the biology or the behavior of an individual. 5. In the context of this chapter, what does environment mean? Cells can divide in two ways. One type of cell division is mitosis, the other, meiosis. An understanding of meiosis is important for understanding the hereditary transmission of genetic information and the way that genetic diversity comes about. 11. What is the purpose of mitosis? How is the genetic material in one resulting cell related to the genetic material in the other resulting cell?

4 28 Chapter 3 Genetic and Evolutionary Foundations of Behavior 12. Since the cells in all parts of your body (excluding egg and sperm cells) have the same gene content, how can the cells end up being so different from one another cells in your stomach lining versus cells in your brain, for example? 13. Meiosis is the type of cell division that produces or cells. Through the exchange of genetic material and subsequent, several genetically different egg or sperm cells are formed. The number of chromosomes in each egg or sperm cell produced is. In human sexual reproduction, the egg and sperm cells unite, combining their genetic information. 14. The union of an egg and a sperm produces a single new cell called a(n), which contains 23 of chromosomes. This new cell then grows through the process of. Each of these new cells is genetically. 15. Explain the evolutionary advantage of reproducing sexually as opposed to asexually. We often talk about chromosomes in terms of pairs. In the case of humans, we usually say there are 23 pairs of chromosomes, not 46 chromosomes, although both are true. The pairing is emphasized because it has important consequences. It is not only the chromosomes that are paired but also the genes they carry. (Hint: Look at Figure 3.5 on text page 57.) 17. Different genes that could potentially occupy the same locus on a pair of chromosomes are called. 18. If the two genes paired at a given locus are identical, the individual is at that locus and if the genes are different, the individual is at that locus. 19. What does it mean to say an allele is dominant? to say an allele is recessive? Are all gene pairs either dominant or recessive? Explain. 20. In each of the following cases, assume that there is an allele M which is dominant and an allele m which is recessive. Indicate which allele (M or m) will be expressed in the phenotype for each case. a. The individual is heterozygous. b. The individual is homozygous for M. c. The individual is homozygous for m. 16. Identify the two types of twins, giving two names for each type. How are the twins genetically related in each type? Gregor Mendel is famous for his elegant studies of genetics in peas. Mendel s work, done in the nineteenth century, still offers a clear picture of certain hereditary patterns and gave rise to the notion of paired units of heredity and dominance just discussed. 21. In one experiment, Mendel studied wrinkled-seed peas and round-seed peas. Explain Mendel s breeding procedure.

5 Chapter 3 Genetic and Evolutionary Foundations of Behavior Why did all of the F 1 generation have round seeds? 2. When dogs of the two breeds were crossbred, how did the resulting (F 1 ) offspring behave in the same fear test? 23. Why did three-fourths of the F 2 generation have round seeds and the other one-fourth wrinkled seeds? (Hint: Look at Figure 3.6 on text page 57.) 3. When dogs of the F 1 generation were mated, what did the researchers observe with respect to the offspring s fearfulness? What conclusion was supported regarding the genetic basis of this type of behavior in cockers and basenjis. Inheritance of Behavioral Traits (pages 58 63) CONSIDER these questions before you go on. They are designed to help you start thinking about this subject, not to test your knowledge. What clues lead scientists to believe that differences among individuals on some specific trait are due to a single gene or to many genes? Can a single gene affect more than one aspect of development or functioning? READ this section of your text lightly. Then go back and read thoroughly, completing the Workout as you proceed. In some cases, a behavioral trait is controlled by a single gene locus and inherited in a Mendelian pattern. Scott and Fuller revealed just such a pattern in the behavior of two dog breeds cocker spaniels and basenjis. Specifically, they showed that a particular behavioral trait was controlled by a single gene locus with one allele dominant over another. (Hint: See Figures 3.7 and 3.8 on text pages 58 and 59.) 1. How did purebred cocker and basenji puppies react when approached by a human who was a stranger to them? 4. Do these results indicate that fear in dogs is controlled by a single gene locus? that environment is irrelevant to the matter of fear in cockers and basenjis? Support your answer. A Mendelian pattern of inheritance is also found to underlie a specific language disorder in the KE family. 5. Describe the specific language disorder found primarily in the KE family. 6. What does the pattern of inheritance for this disorder suggest about its genetic basis? Specifically, is the abnormal gene dominant or recessive?

6 30 Chapter 3 Genetic and Evolutionary Foundations of Behavior 7. What does the normal gene do that the abnormal gene fails to do? 8. Is the normal human version of the gene unique to humans? Explain the significance of this fact. Robert Tryon s work with maze bright and maze dull rats clearly pointed out that even complex behaviors, such as a rat s ability to learn a maze, can be powerfully influenced by genetic variation. 11. How did Tryon produce the two strains of rats? How did he control for the possibility that the rats maze brightness or maze dullness was due to what they learned from their mothers rather than to their genes? Some people have more friends than others. Some people sleep longer on average than others. Some people learn musical skills more easily than others. Most of the differences among individuals reflect the combined influences of many genes (in interaction with the environment, of course), not the effects of single genes. 9. Characteristics affected by many different genes are called traits. When we measure differences among individuals in such traits, they will differ from one another in rather than in type. In other words, individuals will not fall into distinct or groups as they do in the case of single-gene traits. Most often, the set of scores obtained for polygenic traits approximates a(n) distribution. (Hint: Look at Figure 3.10 on text page 61.) Selective breeding has been practiced for thousands of years to produce more desirable strains of plants and animals. Scientists have used selective breeding to produce strains of animals with specialized behavioral tendencies. 10. What is the basic approach followed in selective breeding? 12. Why is it important to note that Tryon tested his subjects only on their ability to learn one particular task? Psychologists often would like to assess the relative contributions of genetic and environmental variation for polygenic behavioral traits in humans. 13. How can such questions be studied in humans? Evolution by Natural Selection (pages 63 66) CONSIDER these questions before you go on. They are designed to help you start thinking about this subject, not to test your knowledge. Since evolution is supposed to involve adaptation, how does nature know which traits will be adaptive in future generations? Can individuals inherit traits that their parents have acquired through experience? How fast does evolution take place?

7 Chapter 3 Genetic and Evolutionary Foundations of Behavior 31 READ this section of your text lightly. Then go back and read thoroughly, completing the Workout as you proceed. The publication of Charles Darwin s The Origin of Species in 1859 was a landmark event. It has had tremendous impact on the way we understand both biological and psychological issues. Darwin used the familiar concept of selective breeding which he termed artificial selection as a point of reference. His major point was that nature, too, involves a kind of selective breeding. He called this natural selection. 1. Explain the concept of natural selection. Evolutionary change is propelled by environmental change. 5. Specify some aspects of the environment that might change and thereby lead to evolutionary change? 6. Is evolutionary change always slow and steady? Support your answer with an example and use the term observed evolution in your answer. Darwin developed his theory without knowing anything about genes. Mendel s work, a first step toward understanding genes, was not yet known in the scientific world. Darwin knew only that something existed that was passed on from one generation to the next and something that could change, forming the basis for evolutionary changes in a species. 2. List two sources of the genetic variability that is the foundation of evolution. Which is the ultimate source of genetic variation? 3. What is a mutation? Is it likely to be helpful or harmful? How does this fit in with natural selection? 7. Can complex genetic changes occur as rapidly as simpler changes? Why or why not? People sometimes fall into intellectual traps in thinking about evolution. Several related misconceptions stem from the mistaken assumption that evolution involves foresight. 8. State three specific forms this fundamental misunderstanding can take. a. b. c. 4. Explain Lamarck s notion of the inheritance of acquired characteristics. Is this idea accepted today? Natural Selection as a Foundation for Functionalism (pages 67 70) CONSIDER these questions before you go on. They are designed to help you start thinking about this subject, not to test your knowledge.

8 32 Chapter 3 Genetic and Evolutionary Foundations of Behavior Why do newborn infants tightly grasp objects placed in their hands? How can we even attempt to discover the reasons for behaviors that evolved in the very distant past? Did every characteristic of a species evolve for a particular purpose? 4. Are ultimate and proximate explanations of behavior necessarily incompatible? Support your answer. READ this section of your text lightly. Then go back and read thoroughly, completing the Workout as you proceed. Psychologists are of course interested in the effects of evolution on behavior. 1. Briefly explain how the process of natural selection can affect behavior. An ultimate explanation may be plausible, even elegant, and yet be incorrect. We must be careful to insist on scientific evidence in evaluating an explanation. 5. What kinds of evidence can be used to evaluate a particular ultimate explanation? 2. How compatible is the functionalist approach in psychology with an evolutionary perspective on behavior? We must also realize that a characteristic doesn t necessarily exist because it is in itself useful. 6. Briefly present four reasons why a given trait or behavior may not be functional. a. Psychologists and biologists who take an evolutionary perspective distinguish between two kinds of explanations of behavior. 3. Define the terms below. a. ultimate explanation b. c. d. b. proximate explanation Natural Selection as a Foundation for Understanding Species-Typical Behaviors (pages 70 78) CONSIDER these questions before you go on. They are designed to help you start thinking about this subject, not to test your knowledge.

9 Chapter 3 Genetic and Evolutionary Foundations of Behavior 33 Are there certain behaviors that seem to mark a dog as doggy or a fish as fishy or a person as human? Do facial expressions mean the same thing across different cultures, or does each culture develop its own code? 4. Comment on the role of learning in the development of species-typical behaviors. Give two examples. READ this section of your text lightly. Then go back and read thoroughly, completing the Workout as you proceed. Behavior patterns so characteristic of a species that they help to identify the species, such as dam building in beavers or speaking in humans, are called instinctive or species-typical behaviors. Human emotional expressions can be regarded as examples of species-typical behaviors. This idea was advanced by Darwin and has been supported by recent scientific research. 1. What kind of atlas did Paul Ekman and Wallace Friesen produce and how did they do it? (Hint: See Figure 3.14 on text page 71.) It is the degree of biological preparedness involved in a behavior that determines whether we call it speciestypical. 5. What is biological preparedness? Illustrate the concept with either human walking or human talking. 6. Why is it better to treat species-typical behavior as a relative concept rather than an absolute one? 2. Summarize Eibl-Eibesfeldt s evidence for the universality of the eyebrow flash. An important means of better understanding human traits (or the traits of any given species) is to compare species. The similarities found can be enlightening. 7. It is important to distinguish two different classes of cross-species similarities. (Hint: See Figures 3.17 and 3.18 on text page 75.) 3. Does it necessarily follow that a universal nonverbal signal like the eyebrow flash is free of cultural influence? Justify your answer. a. A(n) is any similarity between species that exists because of convergent evolution. b. A(n) is any similarity between species that exists because of their common ancestry. c. has taken place when different species independently evolve a common characteristic because they have similar habitats or lifestyles.

10 34 Chapter 3 Genetic and Evolutionary Foundations of Behavior 8. In practice, how can we distinguish between similarities based on homology and those based on analogy? Analogies can also provide clues about species-typical traits. 13. How are analogies useful? What can they not tell us? 9. What is the particular value of studying homologies? Evolutionary Analyses of Mating Patterns (pages 78 84) Homologies have been useful in understanding the evolution of smiling, laughing, and other behaviors. 10. Two kinds of human smiles can be differentiated: Describe them briefly. 11. What is the silent bared-teeth display seen in monkeys and apes? What kind of human smile is it thought to be related to? What can we learn from comparing the way this display functions in macaques and chimpanzees? 12. What is the relaxed open-mouth display seen in monkeys and apes? What is its apparent meaning? How is it related to laughing and the happy smile in humans? CONSIDER these questions before you go on. They are designed to help you start thinking about this subject, not to test your knowledge. Is sexual jealousy adaptive? Why do some species have long-term male-female sexual relationships while others do not? Can human mating behavior be reasonably explained in evolutionary terms? Why are males bigger and stronger than females in some species and not in others? READ this section of your text lightly. Then go back and read thoroughly, completing the Workout as you proceed. Patterns of mating are an especially interesting area of study because mating is critical to the survival of any sexual species and because mating is a fundamental social behavior. 1. In, one male mates with more than one female. In, one female mates with more than one male. In, one male mates with one female. In, members of a group containing more than one male and more than one female mate with one another. Robert Trivers has related various patterns of courtship and mating behavior to a concept he calls parental investment.

11 Chapter 3 Genetic and Evolutionary Foundations of Behavior What does Trivers mean by the term parental investment? 6. How do sex differences in the polyandrous species known as spotted sandpipers support Trivers s theory? 3. What general principle relates parental investment to courtship and mating patterns in Trivers s theory? By far the most common mating pattern for birds is monogamy. 7. What conditions should lead to equal parental investment and thus monogamy? Polygyny is the most common mating pattern among mammalian species. 4. According to Trivers, why does high female parental investment and low male parental investment lead to each of the following? a. polygyny 8. How is equal parental investment related to sex differences in size and strength? b. large size of males 9. In what kinds of species is monogamy common? Give specific examples. c. high selectivity in the female s choice of a mate 10. What evolutionary reasons might underlie the fact that social monogamy is not always matched by sexual monogamy? The primary mating pattern for some species of fish and birds is polyandry. 5. Why does polyandry make more sense for egglaying species than for mammals? Chimpanzees and bonobos are among the clearest examples of species that have a polygynandrous mating pattern.

12 36 Chapter 3 Genetic and Evolutionary Foundations of Behavior 11. What evolutionary advantages might be conferred by polygynandry in chimpanzees and bonobos? 16. In evolutionary terms, why might unfaithfulness occur? 12. Contrast mating behavior in bonobos with that in chimpanzees. Evolutionary Analyses of Hurting and Helping (pages 84 90) Human mating patterns lie somewhere between monogamy and polygyny. Long-term mating bonds are the norm everywhere. Where it is legal, polygyny exists, with some men having two or more wives, but even in such cultures, most marriages are monogamous. 13. How does the mix of monogamy and polygyny in humans fit with Trivers s theory? CONSIDER these questions before you go on. They are designed to help you start thinking about this subject, not to test your knowledge. Do animals help each other or is that an exclusively human phenomenon? Why are men generally more violent than women? READ this section of your text lightly. Then go back and read thoroughly, completing the Workout as you proceed. In the text, aggression refers to fighting and threats of fighting among members of the same species. In humans, the emotions of romantic love and sexual jealousy serve important functions. 1. Why have brain mechanisms that motivate and organize aggression developed? 14. How widespread are these emotions in humans? What evolutionary purposes do they serve? 2. In mammals (especially primates), how do males and females differ in terms of aggression? Why might this be the case? 15. How do humans compare with other species in terms of love and jealousy? 3. Does this sex difference also apply to humans? Lust and unfaithfulness also appear to have an evolutionary foundation.

13 Chapter 3 Genetic and Evolutionary Foundations of Behavior Briefly discuss the exception to the rule found in Bonobos. 9. Has behavior consistent with reciprocity theory been observed in the animal world? among humans? Though members of a given species may fight with one another even to the point of injury or death, they may also help one another. Help sometimes takes the form of cooperation, and at other times appears to be altruistic. 5. Correctly identify each of the following. a. occurs when an individual helps another at the expense of its own survival or reproductive capacity. b. is any behavior that increases the survival or reproductive capacity of another individual. c. involves an individual s helping another while at the same time helping itself. 6. How does kin selection theory explain the occurrence of apparently altruistic behavior? 10. In what sense are both theories attempting to redefine altruistic behavior as not really altruistic? In considering human behavior from an evolutionary perspective we must be aware of certain fallacies that can lead to distorted conclusions. 11. What is the naturalistic fallacy? Illustrate your answer with an example of such distorted thinking. 7. What evidence supports kin selection theory as it applies to animals? to humans? 12. What is the deterministic fallacy? Illustrate your answer with an example of such distorted thinking. 8. How does reciprocity theory explain the occurrence of apparently altruistic behavior? Be sure to READ the Concluding Thoughts at the end of the chapter. Note important points in your Workout. Then consolidate your learning by answering the focus questions in the margins of the text. After you have studied the chapter thoroughly, CHECK your understanding with the Self-Test that follows.

14 38 Chapter 3 Genetic and Evolutionary Foundations of Behavior Self-Test 1 Multiple-Choice Questions 1. Genes that can occupy the same locus and can thus pair with one another are called: a. homozygous. c. alleles. b. dizygotic. d. dominant genes. 2. Suppose a person well-informed in the area of genetics refers to genes for spatial ability. A correct interpretation of this phrase would be: a. genes that directly control a person s ability to process spatial information and have no other function. b. genes that produce a particular anatomy and physiology, which in turn affect a person s spatial ability. c. genes that directly control cognitive ability in general and spatial ability in particular. d. that it s a joke since genes have no effect (direct or indirect) on psychological functioning. 3. Meiosis results in egg and sperm cells containing number of chromosomes contained in each of the body s other cells. a. exactly the same c. twice the b. half the d. four times the 4. The value of sexual as opposed to asexual reproduction is the production of offspring that are: a. genetically diverse. b. genetically uniform. c. genetically similar to their parents. d. numerous. 5. Genes affect both physical development and behavior by directing the synthesis of: a. DNA. b. chromosomes. c. alleles. d. structural proteins and enzymes. 6. The majority of violence carried out by male primates is related somehow to: a. protection of offspring. b. competition for food and water. c. competition for territory. d. sex. 7. Any characteristic that varies in a continuous fashion in a population should be presumed: a. to be polygenic. b. to be based on a single gene. c. to involve whole chromosomes rather than individual genes. d. not to be genetically influenced. 8. Tryon s attempt to selectively breed maze bright and maze dull rats: a. resulted in failure. b. showed that only very small differences could be produced, even over 20 generations. c. showed that large differences could be produced over several generations. d. proved that genes are more important than environment in determining intelligence. 9. In the process called natural selection: a. the breeding of certain domestic animals is controlled to produce desirable traits in future generations. b. inherited traits helpful in overcoming barriers to survival and reproduction are more likely to be passed down to offspring. c. genes that will be helpful in suiting offspring to future environments are selected for. d. nature selects the traits of the next generation by way of a random shuffle of genes. 10. If chance factors alone cause the gene pools in two populations of a species to differ, we refer to the situation as: a. genetic drift. c. artificial selection. b. mutation. d. a homology. 11. The rate of evolutionary change: a. is slow and steady. b. depends primarily on population size. c. depends on environmental change. d. was initially rapid but has slowed progressively over the years. 12. John W. believes that male aggression toward women is controlled by genes and is an unchangeable fact of human nature. His thinking illustrates: a. reciprocity theory. b. kin-selection theory. c. the naturalistic fallacy. d. the deterministic fallacy. 13. Similarities between species that are due to convergent evolution are called: a. analogies. b. homologies. c. analogies in mammals and homologies in nonmammalian species. d. homologies in mammals and analogies in nonmammalian species. 14. The ability of premature human infants to support their weight with the grasp reflex is probably an example of: a. the inheritance of acquired characteristics. b. a vestigial characteristic.

15 Chapter 3 Genetic and Evolutionary Foundations of Behavior 39 c. a genetic side effect. d. reciprocity. 15. According to Robert Trivers, polygyny is related to parental investment. a. high female/low male b. low female/high male c. equal male and female d. no particular pattern of Essay Questions 16. Discuss the opinions (and where possible, the evidence) offered by Darwin, Ekman and Friesen, and Eibl-Eibesfeldt regarding the idea that human emotional expressions are species-typical. Self-Test 2 Multiple-Choice Questions 1. Which of the following is true of polygenic effects? a. Most measurable differences between people can be explained in terms of single genes; that is, they are not polygenic. b. Without examining the genetic material itself, there is no way to determine whether a characteristic is polygenic in origin. c. Polygenic effects are generally brain disorders, while single-gene effects are positive, useful traits. d. The distribution of scores for a polygenic trait often approximates a normal distribution. 2. The normal human cell (other than egg or sperm cells) contains pairs of chromosomes. a. 12 c. 23 b. 22 d The process by which cells divide for the purpose of normal body growth is: a. mitosis. c. transcription. b. meiosis. d. protein synthesis. 17. Does evolution involve foresight? Explain. 4. We can assume that are genetically identical. a. identical twins b. fraternal twins c. both identical and fraternal twins d. no two people 5. A friend of yours has brown eyes and her mother has blue eyes. If blue is recessive and brown is dominant, you can conclude that your friend: a. is heterozygous for eye color. b. is homozygous for eye color. c. is monozygotic for eye color. d. is brown-eyed as far as phenotype is concerned, but you can infer nothing about her genotype. After you have assessed your understanding on the basis of Self-Test 1 and have tried to strengthen your preparation in any areas of weakness, GO ON to Self-Test When Mendel crossed purebred wrinkled-seed peas with purebred round-seed peas, he found that all of the F 1 generation had round seeds. When he bred the F 1 peas with one another, he found that: a. the F 2 peas all had round seeds. b. the F 2 peas all had wrinkled seeds. c. half the F 2 peas had round seeds and the other half had wrinkled seeds. d. three-fourths of the F 2 peas had round seeds and the other one-fourth had wrinkled seeds.

16 40 Chapter 3 Genetic and Evolutionary Foundations of Behavior 7. Recent molecular research had led some scientists to expand the definition of: a. DNA. b. genes. c. amino acids. d. all of the above. 8. Which of the following is true of mutations? a. Mutations have little effect on the course of evolution because they are so rare. b. Mutations are errors in the replication process; as such, they inevitably lead to harmful changes in the structure of DNA. c. Although mutations usually have harmful consequences, they are sometimes helpful. d. Mutations are the new collections of genes that result from the random rearrangement of genes in sexual reproduction. 9. Which of the following represents a question posed from a functionalist perspective? a. At what rate does evolution take place? b. Which species are most closely related to one another? c. What are the possible uses of the human voice? d. Why do dogs have such a keen sense of smell? 13. A species in which an individual female mates with several males would be classified as: a. polygynandrous. c. polygynous. b. polyandrous. d. monogamous. 14. Female bonobos dominate males by virtue of their: a. greater size and strength. b. greater intelligence. c. greater speed and agility. d. strong alliances. 15. When we assume that human genetic biases toward certain behaviors cannot be countered by learning or culture, we are falling prey to the fallacy. a. deterministic c. naturalistic b. species-typical d. genetic dominance Essay Questions 16. Give evidence of the fact that male primates are generally more violent than female primates and discuss it from an evolutionary perspective. 10. The human taste for sugar, which may have several negative health consequences, can be understood as a: a. vestigial characteristic. b. genetic side effect. c. species-typical behavior. d. result of nutritional deprivation. 11. Birds, some insects, and some mammals can fly. Similarities among these groups are not due to common ancestry and would thus represent: a. homologies. b. analogies. c. vestigial characteristics. d. learning. 17. How can we explain behavior that appears to be altruistic? Isn t such behavior entirely inconsistent with natural selection? 12. An ultimate explanation of behavior is an explanation of: a. the mechanism that actually produces the behavior. b. the immediate environment conditions that bring on the behavior. c. the form a behavior will ultimately take upon further evolution. d. why a particular evolutionary development offered an adaptive advantage.

17 Chapter 3 Genetic and Evolutionary Foundations of Behavior 41 Answers Introduction and Review of Basic Genetic Mechanisms 2. protein; structural; enzymes; amino acids; 20; DNA 7. genotype; phenotype 8. chromosomes egg; sperm; random; cell divisions; zygote; pairs; mitosis; unique 17. alleles 18. homozygous; heterozygous 20. a. M, b. M, c. m Inheritance of Behavioral Traits 9. polygenic; degree; categories; normal Natural Selection as a Foundation for Understanding Species-Typical Behaviors 7. a. analogy b. homology c. convergent evolution Evolutionary Analyses of Mating Patterns 1. polygyny; polyandry; monogamy; polygynandry Evolutionary Analyses of Hurting and Helping 5. a. Altruism b. Helping c. Cooperation Self-Test 1 1. c. (p. 57) 2. b. Genes have their effect only by influencing the manufacture of proteins. In that way, they affect an individual s anatomy and physiology. Their effects on behavior are due to the particular anatomy and physiology they create and are thus indirect. (p. 55) 3. b. There are 23 pairs of chromosomes in most of the body s cells, but only 23 chromosomes in an egg or sperm cell. When the egg and sperm combine to form the zygote, the full complement of 23 pairs of chromosomes is restored. (p. 55) 4. a. Sexual reproduction essentially shuffles the genetic deck to produce great diversity in offspring. Diversity offers an evolutionary advantage in that some of the many different types of individuals created may be capable of adapting more successfully to changing environmental conditions and may thus survive and reproduce. (p. 57) 5. d. (p. 53) 6. d. (p. 85) 7. a. A polygenic characteristic can often be described in terms of a normal distribution. A singlegene kind of pattern is indicated by step-wise variation. It involves a categorical rather than a graded difference. (p. 61) 8. c. (pp ) 9. b. Remember that natural selection acts to produce offspring better suited to the current environment, not some future environment. Natural selection is driven by success or failure in that current environment. It cannot be affected by an unforeseen future. (p. 64) 10. a. (p. 69) 11. c. (p. 65) 12. d. (p. 89) 13. a. Convergent evolution refers to a situation in which similarities of environment or lifestyle lead to similar but independent evolutionary developments. The root of the similarity is not genetic relatedness. In this case, we have an analogy, not a homology. (p. 75) 14. b. It may help to remember that a vestige is a leftover trace of something from the past. (p. 68) 15. a. (p. 79) 16. Darwin, Ekman and Friesen, and Eibl-Eibesfeldt have all argued for the idea that we humans are biologically predisposed to express some emotions in species-typical ways. Ekman and Friesen developed an atlas of six basic emotional expressions that people exhibit and found widely differing cultures agreed on what constituted each of them. Eibl-Eibesfeldt found that certain nonverbal signals, such as the eyebrow flash, are universal. He also found that children born

18 42 Chapter 3 Genetic and Evolutionary Foundations of Behavior blind nevertheless displayed emotion in the same way that sighted children do though they could not have learned to do so through observation. (p. 71) 17. One of the most common errors people make in thinking about evolutionary adaptation is to assume it involves foresight. It does not. Natural selection operates on the basis of the current environment, not on the basis of some future environment. This should be clear when we consider the way natural selection operates. Selection comes about only because individuals with genes helpful in overcoming obstacles to reproduction pass those genes on, whereas individuals with unhelpful or harmful genes will tend not to pass them on since they will have fewer or no offspring. Future environments can t sort individuals into those two categories those who successfully reproduce and those who don t. Only the present environment can. (p. 66) Self-Test 2 1. d. (p. 61) 2. c. (p. 54) 3. a. (p. 55) 4. a. (p. 56) 5. a. Since your friend s mother has blue eyes and blue is recessive, you know her genotype; she has two blue-eye alleles. Since your friend received one of her genes for eye color from her mother, she must have one blue-eye allele. Since she s brown-eyed, the other allele must be a dominant brown-eye allele from her father. (p. 56) 6. d. The original purebred round-seed peas had only round-seed alleles to contribute to offspring, whereas purebred wrinkled-seed peas had only wrinkled-seed alleles. In the F 1 generation, all peas have one round-seed allele and one wrinkled-seed allele. Because the F 1 generation all had round seeds, we know that round-seed alleles are dominant. When F 1 peas are bred with one another, one-fourth of the peas will have two wrinkled-seed alleles, one-fourth will have two round-seed alleles, and the remaining peas will have one of each type of allele. But because round-seed alleles are dominant, all but the onefourth with two wrinkled-seed alleles will be round-seeded. (p. 57) 7. b. (p ) 8. c. As the text states, mutation is ultimately the basis of all genetic variation, because it alone introduces truly new genetic information. (pp ) 9. d. The functionalist seeks to understand actual behaviors, not potential behaviors, and the ways they promoted survival and reproduction in the species. (p. 67) 10. a. (pp ) 11. b. The case described is one resulting from convergent evolution. (p. 75) 12. d. (p. 67) 13. b. (p. 78) 14. d. (p. 86) 15. a. (p. 89) 16. Male primates are more aggressive than female primates as a general rule. Female aggression occurs, but is more limited in scope, severity, and frequency. Male aggression often has to do with sex. Male monkeys and apes may kill infants fathered by others to stop their mothers from lactating so they will again be available sexually. They may fight with other males to improve their status and attractiveness and may violently force females to submit to sex. The pattern holds for humans, with men being much more violent than women; sexual jealousy is a primary motive. Such male aggression increases the chances of the male passing on his genes. There is not such an advantage for females given their higher parental investment. (p. 85) 17. Both kin-selection and reciprocity theories try to reframe behavior that is apparently selfless as behavior that is in some sense selfish. Kin-selection theory suggests that the gene promoting the altruistic act in an individual may be destroyed, but other copies of the same gene in the individual s kin will be saved as a result; in this case, it is the gene that is selfish. In reciprocity theory, there is an expectation of the favor being returned at some future time. This theory can help to explain behavior that seems altruistic being directed toward non-kin. Female coalitions among bonobos are an example from animal behavior. Humans are the greatest practitioners of reciprocal helping, though. They have effective ways to keep track of help given, and emotions such as a sense of fairness that promote reciprocity. (p. 88)