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Chapter 2

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Psychology 2220A/B
Scott Mac Dougall- Shackleton

Chapter 2: Evolution, Genetics, and Experience • We all tend to think about things the ways that have been ingrained in us by our Zeitgeist, the general intellectual climate of our culture • You are the intellectual product of a Zeitgeist that promises ways of thinking about the biological bases of behavior that are inconsistent with the facts THINKING ABOUT THE BIOLOGY OF BEHAVIOR: FROM DICHOTOMIES OF INTERACTIONS • We tend to ignore the subtleties, the inconsistencies, and complexities of our existence and to think in terms of simple mutually exclusive dichotomies: right-wrong, good-bad, attractive-unattractive, and so on • The allure of this way of thinking is its simplicity • Is it physiological, or is it psychological • Rene Descartes argued that the universe is composed of two elements: 1. Physical matter, which behaves according to the laws of nature and is thus a suitable object of scientific investigation 2. The human mind which lacks physical substance, controls human behavior, obeys no natural laws, and is thus the appropriate purview of the Church • Cartesian dualism, as Descartes philosophy became known, was sanctioned by he Roman Church, and so the idea that the human brain and the mind are separate entities became even more widely accepted • Is it inherited, or is it learned? • Scholars have debated whether humans and other animals inherit their behavior capacities or acquire them through learning, referred to as the nature-nurture issue • At the same time that experimental psychology was taking root in North America, ethology was becoming the dominant approach to the study of behavior in Europe • European ethology focused on the study of instinctive behaviors, and it emphasized the role of nature, or inherited factors, in behavioral development • Because instinctive behaviors do not seem to be learned, the early ethologists assumed that they are entirely inherited • Problems with thinking about the biology of behavior in terms of traditional dichotomies • The physiological debate and the nature-or-nurture debate are based on incorrect ways of thinking about the biology of behavior • Physiological-or-Psychological Thinking Runs into Difficulty • There are two lines of evidence against physiological-or-psychological thinking • The first line is composed of the many demonstrations that even the most complex psychological changes can be produced by damage to, or stimulation of, parts of the brain • The second line of evidence is composed of demonstrations that some nonhuman species, particularly primate species, possess abilities that were once assumed to be purely psychological ad thus purely human • Asomatogonsia, a deficiency in the awareness of parts of one’s own body • Asomatognosia typically involves the left side of the body and usually results from damage to the right parietal lobe Chapter 2: Evolution, Genetics, and Experience • Although their brains are less complex than the brains of humans, some species are capable of levels of psychological complexity that were once believed to imply the existence of a human mind • Nature-or-Nurture Thinking Runs into Difficulty • Factors other than genetics and learning were shown to influence behavioral development; factors such as the fetal environment, nutrition, stress, and sensory stimulation also proved to be influential • Next, it was argued convincingly that behavior always develops under the combined control of both nature and nurture not under the control of one or the other • Like earlier versions of the nature-or-nurture question, the how-much-of-it-is- genetic-and-how-much-of-it-is-the-result-of-experience version is fundamentally flawed • The problem is that it is based on the premise that genetic factors and experiential factors combine in an additive fashion - that a behavioral capacity, such as intelligence, is created through the combination or mixture of so many parts of genetics and so many parts of experience, rather than through the interaction of genetics and experience • It is nonsensical to try to understand interactions between two factors by asking how much each factor contributes • It is sufficient for you to appreciate three general points: 1. Neurons become active long before they are fully developed 2. The subsequent course of their development depends greatly on their activity, much of what is triggered by external experiences 3. Experience continuously modifies genetic expression • A Model of the Biology of Behavior • The biology of behavior that has been adopted by many biospsychologists • Like other powerful ideas, it is simple and logical • This model boils down to the single premise that all behavior is the product of interactions among three factors 1. The organism’s genetic endowment, which is a product of its evolution 2. Its experience 3. Its perception of the current situation HUMAN EVOLUTION • Darwin was not the first to suggest that species evolve from preexisting species, but he was the first to amass a large body of supporting evidence and the first to suggest how evolution occurs • Darwin presented three kinds of evidence to support his assertion that species evolve: 1. He documented the evolution of fossil records through progressively more recent geological layers 2. He described striking structural similarities among living species, which suggested that they had evolved from common ancestors 3. He pointed to the major changes that had been brought about in domestic plants and animals by programs of selective breeding • Darwin argued that evolution occurs through natural selection Chapter 2: Evolution, Genetics, and Experience • He pointed out that the members of each species vary greatly in their structure, physiology, and behavior, and that the heritable traits that are associated with high rates of survival and reproduction are the most likely ones to be passed on to future generations • Fitness, in the Darwinian sense, is the ability of an organism to survive and contribute its genes to the next generation • True, evolution is a theory, but that does not mean that it is a vague, unreliable speculation: A scientific theory is an explanation that provides the best current account of some phenomenon based on the available evidence • Evolution and Behavior • Some behaviors play an obvious role in evolution • Other behaviors play a role that is less obvious but no less important • Two examples are social dominance and courtship display • Social Dominance •The males of many species establish a stable hierarchy of social dominance through combative encounters with other males •Once a hierarchy is established, hostilities diminish because the low-ranking males learn to avoid or quickly submit to the dominant males •Social dominance an important factor in evolution. One reason is that in some species dominant males copulate more than non-dominant males and thus are more effective in passing on their characteristics to future generations •Another reason why social dominance is an important factor in evolution is that in some species dominant females are more likely to produce more, and more healthy, offspring • Courtship Display •An intricate series of courtship displays precedes copulation in many species •But copulation is unlikely to occur if one of the pair fails to react appropriately to the signs of the other •Courtship displays are thought to promote the evolution of new species •A species is a group of organisms that is reproductively isolated form other organisms; that is, the members of a species can produce fertile offspring only by mating with members of the same species •A new species begins to branch off form an existing species is when some barrier discourages breeding between subpopulation of the existing species and the remainder of the species •Once such a reproductive barrier forms, the subpopulation evolves independently of the remainder of the species until cross-fertilization becomes impossible •The reproductive barrier may be geographical or behavioral •Conspecies (members of the same species): only the suitable exchange of displays between a courting couple will lead to reproduction • Course of Human Evolution • Evolution of Vertebrates •Complex multicellular water-dwelling organisms first appeared on earth about 600 million years ago •About 150 million years laters later, the first chordates evolved Chapter 2: Evolution, Genetics, and Experience •Chordates are animals with dorsal nerve cords •The first chordates with spinal bones to protect their dorsal nerve cords evolved about 25 million years later •The spinal bones are called vertebrae and the chordates that possess them are called vertebrates •Today, there are seven classes of vertebrates: three classes of fishes, plus amphibians, reptiles, birds, and mammals • Evolution of Amphibians •About 410 million years ago, the first bony fishes started to venture out of the water •Fishes that could survive on land for brief periods of time had two great advantages: They could escape from stagnant pools to nearby fresh water, and they could take advantage of terrestrial food sources •So it was that the first amphibians evolved about 400 million years ago •Larval form must live in the water; only adult amphibians can survive on land • Evolution of Reptiles • About 300 million years ago, reptiles evolved form a branch of amphibians • Reptiles were the first vertebrates to lay shell-covered eggs and to be covered by dry scales • Once hatched, a reptile can live far from water • Evolution of Mammals • About 180 million years ago, during the height of the age of dinosaurs, a new class of vertebrates evolved from one line of small retiles • Eventually, mammals stopped laying eggs; instead, the females nurtured their young in watery environments of their bodies until the young were mature enough to be born • Primates have proven particularly difficult to categorize because there is no single characteristic that is possessed by all primates but no other animals • Chimpanzees are the closest living relatives of humans • Evolution of Humankind • Primates of the family that includes humans are the hominins • The first Homo Species are thought to have evolved form one species of Australophithecus about 2 million years ago • Although the big three human attributes - brain, upright posture, and free hands with an opposable thumb - have been evident for hundreds of years, most human accomplishments are of recent origin • Thinking about Human Evolution • Commonly misunderstood points about evolution •Evolution does not proceed in a single line •We humans have little reason to claim evolutionary supremacy •Evolution does not always proceed slowly and gradually. Rapid evolutionary changes can be triggered by sudden changes in the environment or by adaptive genetic mutations •Few products of evolution have survived to the present day - only the tips of branches of the evolutionary bush have survived Chapter 2: Evolution, Genetics, and Experience •Evolution does not progress to preordained perfection - evolution is a tinkerer, not an architect •Not all existing behaviors or structures are adaptive. The incidental non- adaptive evolutionary by-products are called spandrels •Not all existing adaptive characteristics evolved to perform their current functions • Some characteristics, called exaptations, evolved to perform one function and were later co-opted to perform another •Similarities among species do not necessarily mean that the species have common evolutionary origins • Structures that are similar because they have a common evolutionary oigin are termed homologous; structures that are similar but do not have a common evolutionary origin are termed analogous • The similarities between analogous structures result form convergent evolution, the evolution in unrelated species of similar solutions to the same environmental demands • Evolution of the human brain • Early research on the evolution of the human brain focused on size • This research was stimulated by the assumption that brain size and intellectual capacity are closely related - an assumption that quickly ran into two problems •First, it was shown that modern humans, whom modern humans believe to be the most intelligent of all creatures, do not have the biggest brains •Second, the sizes of the brains of acclaimed intellectuals were found to be unremarkable, certainly no match for their gigantic intellects • There is no clear relationship between overall human brain size and intelligence • On obvious problem in relating brain size to intelligence is the fact that larger animals tend to have larger brains • This problem led to the proposal that brain weight expressed as a percentage of total body weight might be a better measure of intellectual capacity • A more reasonable approach to the study of brain evolution has been to compare the evolution of different brain regions • For example, it has been informative to consider the evolution of the brain stem separately form the evolution of the brain stem separately form the evolution of the cerebrum • In general, the brain stem regulates reflex activities that are critical for survival, whereas the cerebrum is involved in more complex adaptive processes such as learning, perception, and motivation • Three important points about the evolution of the human brain •It has increased in size during evolution •Most of the increase in size has occurred in the cerebrum •An increase in the number of convolutions - folds on the cerebral surface - has greatly increased the volume of the cerebral cortex, the outermost layer of cerebral tissue • Although there are differences among the brains of related species, there is a fundamental similarity: all brains are constructed of neurons, and the neural Chapter 2: Evolution, Genetics, and Experience structures n the brains of one species can usually be found in the brains of related species • Human abilities appear to result from the modification of abilities fond in our closest evolutionary relatives • Evolutionary Psychology: Understanding Mate Bonding • A new field of psychology, termed evolutionary psychology • Evolutionary psychologists try to understand human behaviors through a consideration of the pressures that led to their evolution • Promiscuity is a mating arrangement in which the members of both sexes indiscriminately copulate with many different partners during each mating period • The males and females of some species form mating bonds with members of the other sec • Most mammals tend to form mating bonds • The pattern of mate bonding that is most prevalent in mammals is polygyny, an arrangement in which one male forms mating bonds with more than one female • Evidence suggests that polygyny evolved as the predominant pattern of mate bonding in mammals because female mammals make a far greater contribution to the rearing of their young • One major consequence of this common one-sided mammalian parenting arrangement is that the females of most mammalian species can produce only a few offspring during their lifetimes, whereas males have the capacity to sire many offspring • It is important that she mate with particularly fit males, this increases the likelihood that her offspring will be fit and will pass on her genes, along with those of her mate, to the next generation; it also increases the likelihood that what little parental support her offspring will receive form their father will be effective • The males of most mammalian species will form mating bonds with as many females as possible • The inevitable consequence of the selective bonding of female mammals and the nonselective bonding of male mammals in polygyny • Polyandry is a mating arrangement in which one female forms mating bonds with more than one male • Polyandry does not occur in mammals; it occurs only in species in which the contributions of the males to reproduction are greater than those of the females • Because of the selectivity of the females, the competition among the males for reproductive partners becomes fierce, with only the successful competitors passing on their genes • Monogamy is a mate-bonding pattern in which enduring bonds are formed between one male and one female • In such species, any change in the behavior of a female that would encourage a male to bond exclusively with her would increase the likelihood that her heritable characteristics would be passed on to future generations • One such behavioral change is for each female to drive other females of reproductive age away from her mate • Thinking About Evolutionary Psychology Chapter 2: Evolution, Genetics, and Experience • Good theories of behavioral evolution have predictions about current behaviors built into them so that the predictions - and thus the theory - can be tested • The foregoing evolutionary theory of mate bonding has led t several predictions about current aspects of human mate selection • Buss has confirmed several of them: • Men in most cultures value youth and attractiveness in their mates more then women do; in contrast, women value power and earning capacity more then men do • Physical attractiveness best predicts which woman will bond with men of high occupational status • The major mate-attraction strategy of women is increasing their physical attractiveness; in men, it is playing their power and resources • Men are more likely than women to commit adultery • All inherited tendencies are modulated by experience FUNDAMENTAL GENETICS • Mendelian Genetics • Mendel studied inheritance in pea plants • In designing his experiments, he made two wise decisions • to study dichotomous traits, and he decided to begin his experiments by crossing the offspring of true-breeding lines • Dichotomous traits are traits that occur in one form or the other, never in combination • True-breeding lines are breeding lines in which interbred members always produce offspring with the same trait, generation after generation • The results of Mendel’s experiment challenged the central premise on which all previous ideas about inheritance had rested: that offspring inherit the traits of their parents • An organism’s observable traits are referred to as its phenotype: the traits that it can pass on to its offspring through its genetic material are referred to as its genotype • Mendel devised a theory to explain his results • It comprised of four ideas: • First, Mendel proposed that there are two kinds of inherited factors for each dichotomous trait (today we cal this inherited factor a gene) • Second, Mendel proposed that each organism possess two genes for each of its dichotomous traits • The two genes that control the same trait are called alleles • Organisms that possess two identical genes for a trait are said to be homozygous and those that present two different genes are heterozygous • Third, Mendel proposed that one of the two kinds of genes for each dichotomous trait dominates the other in heterozygous organisms • Fourth, Mendel proposed that for each dichotomous trait, each organism randomly inherits one of its father’s two factors and one of its mothers two factors • Chromosomes: Reproduction and Recombination Chapter 2: Evolution, Genetics, and Experience • Chromosomes - the threadlike structures in the nucleus of each cell • Chromosomes occur in matched p
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