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Human Brain - Chapter 12.docx

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University of Toronto Scarborough
Ted Petit

Chapter 12 – Humans, Human Brain and Evolution Evolution of Humans - 1859 > Charles Darwin – all living creatures are subject to selection - physical and beh changes due to selection pressure - little doubt that humans have been and coninue to be subjected to evolutionary forces - evolutionary psychology: attempts to apply the principles of adaption and selection to human beh [increasing in pop.] o provides us with a means by which we can integrate our beh with our prehistory and gain profound insights into what it means to be human - we do not like to think of ourselves as animals and as being subject to the laws of nature Evolution Theory - Charles Darwin and Alfred Russel Wallace > July 1, 1858 > both developed the theory independently [naturalists w/ interests in geology] - Darwin > HMS Beagle > fascinated by how species emerged and how geographic isolation on islands produced such a variety of features in what he presumed were the same species - Wallace > relationship btwn specific geographic locations and their effects on specific characteristics of the species that inhabited that niche o sent his paper to Darwin which confirmed his theory of evolution - on the origins of species, 1859 – Darwin - both are credited with discovering he principles of natural selection but cited other in the production of the theory of evolution: 1. classification of organisms based on structure – Carolus Linnaeus - commonalities in structure of related species 2. Charles Lyell and William smith [geologists] > earth far older than thought - Lyell > some species hardly change, some extinct / smith > erosion, volcanism 3. Thomas Malthus > food supplies affect population a. pop. grow exponentially until they surpass their food supply Historical Theory of Evolution [the original theory of evolution] - variation, inheritance, differential reproduction - all individ vary > diff in morphology > diff can be passed from gen to gen - these diff is morphology > result in variations in success in the enviro > survival and reproduction - Darwin > mechanism underlying these changes > natural selection o all individ are unique and that characteristics that give an animal a reproductive adv will result in the magnification of these traits in the population - when a trait results in a reproductive advantage and is selected for > adaptation [must be inherited from one generation to the next] - diff enviro may result in the selection of diff traits - because the environment is not static and variation never truly goes away natural selection must be continually occurring - second book > sexual selection: a form of selection in which the inheritance of a gene is based on the gene’s ability to help an individual reproduce o competition among individ for reproduction - Intersexual selection: members of one sex choose mates from the opposite sex on the basis of specific traits [men > attractiveness/youth w > physical] - intrasexual selection: members of the same sex compete for partner of the opposite sex - traits are passed on by genes [pieces of DNA that pass traits form gen to gen] and that the original source of variation is the random mutation [spontaneous changes to a genes] of these genes Modern Synthesis [modern synthetic theory of evolution] - the current version of evoltuoianry theory is based on what is known about DNA [make up chromosome], chromosomes, and population biology - genes, made of DNA, assort in pairs and are located on chromosomes which are simply strings of genes [23 pairs of chromosomes, 26-40 000 genes] - genetically speaking there is more same in the genetic makeup of individuals tat different [allow for common features among members of our species] - bipedal gait: walking upright on two legs - diff allow for subtle diff among individ - genotype is the entirety of your genetic composition and barring exposure to certain chemical/radiation it remains the same throughout your life - phenotype is the interaction of your genotype with the enviro - regardless of your phenotype only your genotype is passed on to your children - natural selection operates on phenotype/only genotypes are transmitted from gen to gen - genes do not make traits/diseases they make protein - alleles: alternative form of a given gene - when we say there is a gene for blue eyes > we mean > there is an allele for eye color that in one form make a protein that make the iris look brown - Gregor Mendel – Experiments in plant hybridization > 1885 - dominant [ie. brown eyes] genes are always expressed when present - recessive genes are onlyl expressed when there are no dominant genes - when both alleles are the same > homozygous for that trait - when the two alleles are diff > heterozygous for the trait - polygenic > when multiple genes affect a trait o polygenic traits tend to associate [bffs, hair and eye colour] o are additive do not follow the simply dominant/recessive pattern o inherited traits are most likely polygenic - genetic variation > mutations or recombination of DNA - mutation occurs > change in genotype due to an error in replication of DNA o slow, harmful to organism = reduced ability to survive - replication > DNA makes copies of itself - summary of modern synthesis 1. the central tenent of the modern synthesis is that certain enviro select certain phenotypes and phenotypes are an expression of the genotype interacting with the enviro [natural selection can change pheno but not geno] o enviro do not produce adaptation > mutations result in characteristics that in a specific enviro are either adaptive/neutral/ deleterious for the organism 2. although genes occur at the level of the individ, evolutionary change occurs at the level of the populations [pop evolve by changes in gene freq > natural selection, random gene drift, and gene flow] o genetic drift: the tendency for isolated pop to depart from the original genetic composition of the pop o most likely due to inbreeding [offspring resulting from related parents] and adaptation to the isolated enviro o gene flow: the movement of genes through pop that results from mating o since enviro change over time things that were adaptive > maladaptive over time 3. Species represent different gene pools, rather than fundamentally unique groups [judged by their genotype not their phenotype] o considerable genetic overlap among diff species [98.4% chimp/hum] o support that evolution is a gradual process that rends to make small changes over time in existing species rather than new species developing from nothing * 3 major diff btwn the modern synthesis and historical theory 1. modern synthesis recognizes that traits are a result of genes that are inheristed from ones parents and interact w/ the enviro 2. recognizes there are mechanisms other than natural selection that can effect evol change 3. recognition that what we call species are only differences in gene pools of a population, not totally distinct or new organisms that arrived fully formed from nowhere Evolution of the Nervous System - from looking at the skulls of our ancestors we can see > increase in skull size and brain size - we have large brains relative to our body size [2.33% of oru body weight] o tree shrew > 3.33% - the human brain has almost 3.2 times the a
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