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Chapter 12

PSYB65 Chapter 12.docx

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University of Toronto Scarborough
Ted Petit

Sanchika K 10.20.12 PSYB65 Chapter 12 Humans, Human Brains, and Evolution Evolution of Humans  Darwin’s theories tell us that all living creatures have been and continue to be subjects to selection  These principles apply to more than just physical changes evolutionary theory provides important insights into behaviors that also been subjects to selection pressures  Few researchers applied the principles of evolution to human behavior  Little doubt among scientists that humans have been and continue to be subjected to evolutionary forces  Evolutionary psychology o Attempts to apply the principles of adaption and selection to human behavior  Evolutionary perspective on brain and behavior provides us with important insights into how our environment has affected the development of our species as well as the specific demands and subsequent adaptations that evolved to deal with these challenges Evolutionary Theories  Evolutionary theory credited to both Charles Darwin and Alfred Russel Wallace on July 1 1858  Darwin o Sailed the H.M.S Beagle for 5 years in the Galapagos islands o He became intrigued with understanding how species emerged and how geographic isolation on islands produced such a variety of features in what he presumed where the same species  Wallace o Explored the Amazon River o Became intrigued with the relationships between the geography of a particular location and its effects on specifics characteristics of the species that inhabited that niche o Ideas of Darwin and Wallace  The classification of organisms based on structures by Carolus Linnaeus. He observed that there were commonalities in structures among related species  Work by geologists Charles Lyell and William Smith supported the notion that the earth was far older than was previously though  Smith studies fossils and observed that some species of animals had changed very little, while some were extinct  Lyell studied geological process, including erosions and argues that the length of time required for these events to happen suggests that the earth is much older than had previously thought  Thomas Malthus, a philosopher suggested that populations grow exponentially until they surpass their food supply, which leads to a struggle for existence Sanchika K 10.20.12 PSYB65 Historical Theory of Evolution  Summarized by three terms variations, inheritance and differential reproduction  Variation o All individuals vary, which results in differences in morphology o Passed from one generation to another o Individuals difference in morphology results in variations in success in the environment in terms of survival and reproduction  Adaption o Natural selection  All individuals are unique and characteristics that give an animal a reproductive advantage will result in a magnification of that trait in the populations o For a trait to be an adaption, it must be inherited from one generation to another o Different environments may result in the selections of different traits o Sexual selection  Is competition among individuals for reproduction that determine a gene’s fate  Two types  Intersexual selection o One sex chooses a mate from among members of the other sex on the basis of specific traits  Intrasexual selection o Members of the same sex compete for partners of the opposite sex o Historical theory of evolution  Traits are passed on by genes and that the original source of variation is the random mutations of these genes Modern Synthesis  Combines info from molecular biology and paleontology  Based on DNA, chromosomes and population biology  There is a large variation due to mating  More similarities within each other than differences o Such as eyes and bipedal Gait ( being able to walk upright on two legs)  Genotype o Your genetic composition  Phenotype o The interaction of your genotype with the environment in which you develop  More than one form of gene is called allele  Inheritance patterns of genes often follow very simple rules of expressions o First expressed by Gregor Mendel  Dominant gene o Always expressed whenever they are present  Recessive o Expressed only when there are no dominant gene presented  Homozygous o When both alleles are the same  Heterozygous o When the two alleles are different Sanchika K 10.20.12 PSYB65  Polygenic o When multiple genes affect a trait  In any population there is genetic variation o Caused by mutations, occurs when there is a change in the genotype due to an error in the replication of DNA  Summary of the Modern synthesis o The central tenet of the modern synthesis is that certain environments select certain, phenotypes, and phenotypes are an expression of the genotype interacting with the environment o Although genes occur at the level of the individual, evolutionary changes occur at the level of populations  Populations evolve by natural selection, random genetic drift and gene flow  Genetic drift- tendency for isolated populations to depart from the original genetic composition of the population  Causes inbreeding  Gene flow- movement of genes through a population that results from mating o Species represent different gene pools, rather than fundamentally unique groups  Species are judged as such as their genotypes not phenotypes  The differences of modern synthesis theory of evolution and historical theory of evolution o Modern theory recognized that traits are the results of genes that are inherited from ones
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