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Chapter 1

CHAPTER 1 NOTES - Evolutionary Psych

11 Pages
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Department
Psychology
Course Code
PSYC 3420
Professor
Irwin Silverman

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CHAPTER 1: THE SCIENTIFIC MOVEMENTS LEADING TO EVOLUTIONARY PSYCHOLOGY • Understanding the human mind/brain mechanisms in evolutionary perspective is the goal of the new scientific discipline called evolutionary psychology • Evolutionary psychology focuses on four key questions: 1. Why is the mind designed the way it is - that is, what casual process created, fashioned, or shaped the human mind into its current form? 2. How is the human mind designed - what are its mechanisms or component parts, and how are they organized? 3. What are the functions of the component parts and their organized structure - that is, what is the mind designed to do? 4. How does input from the current environment interact with the design of the human mind to produce observable behaviour? LANDMARKS IN THE HISTORY OF EVOLUTIONARY THINKING EVOLUTION BEFORE DARWIN • Evolution refers to change over time • Lamarck believed in two major causes of species change: 1. A natural tendency for each species to progress toward a higher form 2. The inheritance of acquired characteristics • (ex. Giraffes' long necks evolved to reach leaves on top of trees) • Cuvier proposed a theory called catastrophism, according to which species are extinguished periodically by sudden catastrophes, such as meteorites, and then replaced by different species • There is a bewildering variety of species, some with astonishing structural similarities: o Ex. Humans, chimpanzees, and orangutans, all have exactly five digits on each hand and foot o Ex. Wings of a bird are similar to the flippers of a seal • These suggest that perhaps one was modified from the other • This also shows that life was not static • Evidence suggesting change over time also came from the fossil records • Another source of evidence came from comparing the embryological development of different species o Ex. An unusual loop-like pattern of arteries close to the bronchial slits characterizes the embryos of mammals, birds, and frogs • This suggests that species might have come from the same ancestors million years ago • The biologists who believed that organic structure changed over time called themselves evolutionists DARWIN'S THEORY OF NATURAL SELECTION • Darwin went on a five year trip to Galapagos Islands • On his return from the trip, he had discovered the Galapagos Finches, which he had presumed that they were all of the same species, actually varied so much that they constituted different species CHAPTER 1 page 1 •Darwin wanted to account for change, of course, but he also wanted to account for why organisms appeared so well designed for their local environments •The result must be a "struggle for existence" in which favourable variations tent o be preserved and unfavourable traits tend to die •When this process is repeated generation after generation, the end result is the formation of new adaptation •Darwin's answer to all these puzzles of life was the theory of natural selection: 1. Organisms vary in all sorts of way 2. Only some of these variations are inherited 3. Selection - organisms with some heritable variants leave more offspring because those attributes help with the tasks of survival or reproduction •For a species to pass its inherited qualities to future generations, it must reproduce •Thus, differential reproductive success, brought about by the possession of heritable variants that increase or decrease an individual's chances of surviving and reproducing, is the "bottom line" of evolution by natural selection •Differential reproductive success or failure is defined by reproductive success relative to others DARWIN'S THEORY OF SEXUAL SELECTION •Darwin observed several facts that contradicted with his theory of natural selection, also called "survival selection" •First, he noticed weird structures that seemed to have absolutely nothing to do with survival o Ex. The brilliant plumage of peacocks •Second, he noticed that in some species, the sexes differed dramatically in size and structure •His answer to these apparent embarrassments to the theory of natural selection was to devise a second evolutionary theory: the theory of sexual selection •Two primary means of which natural selection could operate: o Intrasexual competition • Competition between members of one sex, the outcomes of which contributed to mating access to the other sex • Ex. Stags locking horns in combat o Intersexual selection • Prefential mate choice - if members of one sex have consensus about the qualities that are desired in members of the opposite sex, then individuals of the opposite sex who possess those qualities will be preferentially chosen as mates • Darwin called the process of intersexual selection "female choice" - because females of many species were discriminating or choosy about whom they mated with THE ROLE OF NATURAL SELECTION AND SEXUAL SELECTION IN EVOLUTIONARY THEORY 1. Natural selection and sexual selection are not the only causes of evolutionary change CHAPTER 1 page 2 • Some changes for example can occur because of a process called genetic drift, which is defined as random changes in the genetic makeup of a population • Random changes come about through several processes, including mutation, founder effects, and genetic bottlenecks • Random changes can arise through a founder effect, which occurs when a small portion of population established a new colony and the founders of the new colony are not entirely genetically representative of the original population o Ex. An increase in genes coding for red hair • Random change can also arise through genetic bottlenecks, which happens when a population shrinks (may be due a catastrophe such as an earthquake) o The survivors of the random catastrophe carry only subset of the genes of the original population • In sum, although natural selection is the primary cause of evolutionary change and the only known cause of adaptation, it is not the only cause of evolutionary change • Genetic drift (as listed above) can also produce a change in genetic makeup of a population 1. Evolution by natural selection is not forward looking and is not "intentional" • Ex. The giraffe does not see the leaves on top of the tree and "evolve" a longer neck, rather those giraffes that, owing to an inherited variant, happen to have longer necks have an advantage over other giraffes in getting to those leaves 1. Selection is gradual, at least when evaluated relative to the human life span • There can be long periods of no change, followed by a relatively sudden change, a phenomenon known as punctual equilibrium • Darwin's natural selection united all species into one grand tree of descent in one bold stroke • Ex. Human beings and chimpanzees share more than 98% of each other's DNA and shared a common ancestor 6 million years ago • Ex. Many human genes turn out to have counterpart genes in a transparent worm called caenorhabditis elegans Objections made to Darwin's theories: 1. Darwinian evolution lacked a coherent theory of inheritance 2. Biologists couldn’t believe how the early stages of the evolution of an adaptation could not be useful to an organism o "Argument from ignorance" refers to the fact of how it's not enough that just because a scientist has a hard time understanding a theory, that the theory is false 3. From religious creationists - many of whom viewed species as immutable (unchanging) and created by a deity than by gradual process of evolution by selection THE MODERN SYNTHESIS: GENESE AND PARTICULATE INHERITANCE • Mendel's discovery that inheritance particulate (not blended) - which he demonstrated that by cross-breeding different strains of pea plants • Gene - smallest discrete unit that is inherited by offspring intact • Genotype - entire collection of genes within an individual CHAPTER 1 page 3 • The unification of Darwin's theory of evolution by natural selection with the discovery of particulate gene inheritance culminated in a movement in the 1930s-40s called the Modern Synthesis THE ETHOLOGY MOVEMENT • Darwin though that his theory of natural selection is just as applicable to behaviour, including social behaviour, as is to physical structures • Evidence that support this view: 1. All behaviour requires underlying physical structures • Ex. Bipedal locomotion is a behaviour and requires the physical structures of two legs and multitude of muscles to support those legs 2. Species can be bred for certain behavioural characteristics using the principle of selection • Ex. Dogs can be bred (artificial selection) for aggressiveness of passivity • Ducks imprint on the first moving object they observe in life - forming an association during a critical period of development • Lorenz started a new branch of evolutionary biology called ethology, and imprinting in birds was a vivid phenomenon used to launch this new field 1. Ethology is defined as the study of the proximate mechanisms and adaptive value of animal behaviour • Ethologists were interested in four key issues, which have become known as the four "whys" of behaviour advanced by one of the founders of ethology, Nikolaas Tinbergen 1. The immediate influences on behaviour (Ex. The movement of the mother) 2. The developmental influences on behaviour (Ex. The events during the duck's lifetime that cause changes) 3. The function of behaviour or the "adaptive purpose" it fulfill (Ex. Keeping the duck close to the mother, which it helps it to survive) 4. The evolutionary or phylogenetic origins of behaviour (Ex. What sequence of evolutionary events led to the origins of an imprinting mechanisms in the duck) • Ethologists developed an array of concepts to describe what they believed to be the innate properties of animals o Fixed action patterns, are the stereotypic sequences an animal follows after being triggered by a well-defined stimulus o Once a fixed action pattern is triggered, the animal performs it to completion o Ex. Showing certain male ducks a certain plastic facsimile of a female duck, will trigger a rigid sequence of courting behaviour THE INCLUSIVE FITNESS REVOLUTION • Hamilton proposed a radical new revision of evolutionary theory, which he termed: inclusive fitness theory • Hamilton reasoned that classical fitness - the measure of an individual's direct reproductive success in passing genes through the production of offspring - was too narrow to describe the process of evolution by selection • He theorized that natural selection favor characteristics that cause an organism's genes to be passed on, regardless of whether the organism produces offspring directly CHAPTER 1 page 4 • Parental care - investing in one's own children - was reinterpreted as merely a special case of caring for kin who carry copies of parent's genes in their bodies • An organism can also increase the reproduction of its genes by helping siblings to survive and reproduce • Hamilton's genius was in the recognition that the definition of classical fitness was too narrow and should be broadened to be inclusive fitness • Technically, inclusive fitness is not a property of an individual or an organism but rather a property of its actions or effects • Thus, inclusive fitness can be viewed as the sum of an individual's own reproductive success (classical fitness) plus the effects the individual's actions have on the reproductive success of his/her genetic relatives • For this second component, the effects on relatives must be weighted by the appropriate degree of genetic relatedness to the target organism (ex. 0.5 for brothers/sisters, 0.25 for grandparents) • Gene is the fundamental unit of inheritance, the unit that is passed on intact in the process of reproduction CLARIFYING ADAPTATION AND NATURAL SELECTION • Williams challenged the prevailing endorsement of group selection, the notion that adaptations evolved for the benefit of the group through the differential survival and reproduction of groups, as opposed to be benefit for the gene arising through the differential reproduction of genes • According to this theory, only species that possessed characteristics beneficial to their group survived • However, this theory is a weak force in evolution • Selection operating on individual differences within a group, undermines the power of selection operating at the level of group • Inclusive fitness theory partially solved the problem of altruism - because altruism could evolve if the recipients of help were one's genetic kin • Another contribution of adaptation and natural selection was called an onerous concept • Adaptation may be defined as evolved solutions to specific problems that contribute either directly or indirectly to successful reproduction o Ex. Sweat glands, may be adaptations that help solve the survival problem of thermal regulation • Williams provided criteria for determining when we should invoke the concept of adaptation: reliability, efficiency, and economy • Adaptation is invoked to explain improbable usefulness • Williams was extremely influential in showing that understanding adaptation requires being "gene-centered" TRIVER'S SEMINAL THEORIES • Trivers three seminal theories: 1. Theory of reciprocal altruism: The conditions under which mutually beneficial exchange relationships or transactions evolve 2. Parental investment theory: which provided a powerful statement of conditions under which sexual selection would occur for each sex CHAPTER 1 page 5 3. The theory of parent-offspring conflict: the notion that even parents and their progeny will get into predictable sorts of conflicts because they share only 50% of their genes THE SOCIOBIOLOGICAL CONTROVERSY • Sociobiology is not generally regarded as containing fundamentally new theoretical contributions to evolutionary theory • Williams book "sociobiology: the new synthesis" created the most controversy • His work sparked attacks from Marxists, radicals, creationists, other scientists • Part of this controversy stemmed from the nature of Wilson's claims o He asserted that sociobiology would "cannibalize psychology" o He speculated that many cherished human phenomena (such as culture, religion, ethics, and even aesthetics) would ultimately be explained by the new synthesis o
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