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Chapter 12


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University of Toronto St. George
Prof Petit

Chapter 12: Humans,Brains, and Evolution Module 12.1: Evolution of Humans - 1859: Origin of Species published by Darwin - insight in which creatures (and behavior) subject to selection - principles of evolution to human behavior - physical evolution controversial because scientists disagree about the mechanisms of evolution - but little doubt about fact humans been subject and will be subject to evolution Evolutionary psychology: principle of adaptation and selection to human behavior - difficulty acceptance: newness and challenges accepted social norms - Difficult to think ourselves as animals subject to natural laws (and used in racism in certain species - evolutionary psychology: means integrate behavior with prehistory and gain profound insight in what it means to be human Evolutionary Theory - discovery of evolution credited to both Charles Darwin and Alfred Russel Wallace on July 1, 1858 to Linnean Society of London: development made independently by both who are naturalist with interest in geology - Darwin travelled with H.M.S Beagle to Galapagos Islands - became interested in how geographic isolation produced variety of features in what he presumed were relate species - Wallace explored Amazon River basic (and Indonesia) - intrigued with characteristic of species inhabited - Wallace wrote “On tendency of varieties to depart indefinitely from Original type” and sent it to Darwin - pushed Darwin to publish On Origin of Species - Darwin and Wallace credited others with providing insight Darwin and Wallace drew include following 1. Classification of organism by Carolus Linnaerus: observed commonalities in structure of related species (commonality supports principle of evolution = Linnaerus did not recognize it at time) 2. Work by geologists Charles Lyell and William Smith = earth older than what people thought Smith - studied fossils and observed some species of animals changed little while others are extinct. - If changes occurred, occurred in predictable manner in strata of earth: more primitive forms occur in oldest version of strata of earth Lyell Chapter 12: Humans,Brains, and Evolution - studied volcanoes and erosion and argued length needed for these processes to occur was much longer than previously thought so earth older than previously thought - process shaped earth was still in effect: forces shaped earth as we know are still in effect 3. Thomas Maltus, philosopher of poverty on population during industrial revolution - food supply affect population - Malthus suggested population grew exponentially until surpassed food supply which leads to struggle for existence ( similar survival of fittest) Historical Theory of Evolution - summarized by variation, inheritance, differential reproduction variation: differences in morphology are characteristics of all individuals inheritance: passing differences in morphology from one generation to next differential reproduction: organisms that are best suited for environment will show enhanced survival and reproduce greater rate than those who are less suited - individuals vary which results in differences in morphology that can be passed down from one generation to the next - differences in morphology result in variations in success in environment, in terms of survival and reproduction - we all vary in height (variation), some of our heights similar to parents (inheritence) - If environment not nice to tall people than, short people have advantage and reproduce more (differential reproduction) - Evolutionary theory more short people than tall natural selection: all individuals are unique and characteristics give an animal reproductive advantage will result in magnification of these traits in population adaptation: when traits result in reproductive advantage - environment not static, natural selection continuously occurring (new species shapped now sexual selecton: form of selection where inheritence of gene is based on gene’s ability to help individual reproduce; 2 types: intersexual and intra sexual intersexual selection: members of one sex choose to mates from opposite sex based on specific traits ( man look for young and attractive women to mate) intrasexual selection: members of same sex compete with each other for partners of opposite sex ( man display wealth more often to impress women) genes: pieces of DNA pass from generation to generation mutation: spontaneous or random changes to gene or genes Chapter 12: Humans,Brains, and Evolution Modern Synthesis: based on DNA (deoxyribonucleic acid), chromosomes, and population biology -chromosomes: pairs of genes ( between 26,000 and 40,000 genes - when egg fertilized, sperm adds 23 chromosomes to egg’s 23 making 23 pairs - this is how variation - even if there is genetic variation, there are similarities - bipedal gait: walk up right vs. eye color - genotype: entire genetic composition; invariant towards exposure of certain chemicals - phenotype: interaction of environment with genotype - natural selection operates on phenotype but only genotype transmitted to generation - genes do not make traits they make proteins - allele: more than one form of given ( allele for eye color ) - find gene: mean we found allele which together with environment produces some of symptoms of Alzheimer Inheritance Pattern of Genes - described by Gregor Mendel in Experiment of Plant Hybridization - recessive: only expressed when there is no dominant - dominant: expressed regardless if it is with dominant or recessive gene - homozygous: both alleles are the same - heterozygous: two alleles are different - polygenic trait: trait controlled by multiple genes ( often on different chromosomes ) - polygenic traits like best friend (go everywhere together) = - Example: brown hair goes with blue eyes and blonde with blue - not just recessive and dominant; each trait plays small part of determining genotype Mutation occurs when there is change in genotype due to error - replication: DNA makes copies of itself - most mutations harmful (reduced ability to survive) to humans = results in different ability to adapt to environment - evolution works by selecting individuals who are better to survive and reproduce, passing genes to offspring Summary of Modern Hypothesis 1. Central Tenet: certain environment selects certain phenotype which are expressions of genotype and environment - environment cannot see genotype but can select phenotype; it can’t change genotype Chapter 12: Humans,Brains, and Evolution - environment affect mutation do not give direction for mutation to occur = it does not produce adaptation - mutation result in characteristics that are adaptive, neutral, adverse for organism in certain environment 2. genes occur at level of individual, evolutionary changes occur at level of population - population evolve changes in gene frequency brought by random genetic drift, natural selection, and gene flow - natural selection produce evolutionary change if gene provides slight fitness - small differences in gene result in large changes in genetic make up in short period if they provide reproductive advantage Gene Drift: tendency for isolated population to depart from original genetic composition ( another way to produce evolutionary change) Gene flow: movement of genes through population that results from mating Gene flow can be profound when there is extensive inbreeding environmental change over time, genes once adaptive become maladaptive and decrease frequency of population 3. species represent different gene pools, rather than fundamentally unique groups - species judged by genotype, not phenotype - if look at phenotype can be mislead: - example: chihuaha and great danes are phenotypically distinct they are both phenotype of dog (and could mate) - 98.4 overlap between chimpanzee and human beings - evolution gradual process but fossil records show periods of stasis and rapid change Differences between modern and historical theory of evolution - traits result of genes are inherited from parents and interact with environment - recognition that are mechanisms other natural selection can effect evolutionary change - species are only differences in gene pools of population, not distinct or new organisms that arrived formed from nowhere Neuropsychological Celebrity ( Children with PKU) - Phenylketonuria (PKU) is rare inherited (autosomal or nonsex chromosome, recessive) disease in metabolism results from deficiency of phenylalanine hydoxylase enzyme - characterized by mental retardation which depends on: - first factor: how early condition is detected: no need of blood test: condition leads to - light skin, light hair, and development of musty odor (excess phenylalanine in skin) - left untreated, PKU results in damage brain and other organs Chapter 12: Humans,Brains, and Evolution - if detected early, phenylalanine kept low dietary management and brain damage it causes can be kept to a minimum - second factor: degree of brain damage produced by PKU is diet - phenylalanine kept from building up by diet with low levels of protein - individual’s genes interact with his environment - genetic abnormality causes PKU can be controlled as long as environment controlled - how disease causing mutations survive: Woolf suggested advantage to PKU: people with one recessive gene protected against effects of Orchratoxin A (mycotoxin appears in stored grains and food) - 2 copies of recessive genes results in maladaptive PKU Evolution of Nervous System - brain tissue is soft and leaves not fossils - from skulls of fossil ancestors we can see increase in skull and brin size - caution against brain size with increased humanness - tend to have one of largest brains for our body (not largest brain) - our brains are 2.33% of body weight, tree shrew is 3.33 % of body weight - brain is 3.2 times amount of cortex in other species - over evolutionary species, increased brain size increase ability to perform complex behavior Endocast: make mold inside of skull - look like brain is covered with meninges, allowing for inspection of major sulci and gyri of brain - brian changes in organization: asymmetrical - degree of asymmetry not pronounced in endocast from austrolophithecines: very early ancestor who lived 4 to 1 million years - suggesting symmetry evolved in our time - Scientists believe placement of sulci on endocast associated with brain organization - frontal lobe associated with language - Homo erectus: demonstrate more human like cortex since Homo erectus lived in 1.6 to 400,000 years, relatively recent change - rudimentary forms of speech - Endocasts in australopithecines and home species do not preserve, so don’t know when feature occurred - Neanderthals are species lives from 250 000 to 30,000 from Europe - endocasts obtained from Neanderthals and from humans, so Neanderthals could use some language - few casts of fossil hominids, makes it difficult to know if change in sulcai position reflects actual evoluntionary change for entire species or just type of individual variation in brain organization Chapter 12: Humans,Brains, and Evolution - study of endocasts flawed but best way - increase size of frontal lobe in austrolopithecines and subsequent hominid brains - switch from olfactory to frontal regions = changes in behavior from olfactory analysis to comple
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