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PSY 814 (1)
Chapter 2

PSY295 - Chapter 2.doc

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Ryerson University
PSY 814
Shavin Malhotra

PSY295 Chapter 2: Origins of the Human Brain and Behaviour - Kanzi, bonobo/pygmy chimpanzee learned symbolic language (Yerkish) and understood complex human speech - humans belong to the primate order along with lemurs, tarsiers, monkeys and apes, all diverging from same common ancestor - cladogram: graph that shows the relative time of origin of various closely related groups - each branch point in a cladogram distinguishes animals positioned before that time point from animals positioned after it by one or more physical or behavioural traits (ex. apes can swing through trees, no primate preceding ape can do so) - in past 5-8 million years, hominids, humanlike ancestors, diverged from ancestral ape lineage by acquiring characteristics that distinguish them from other apes - hominids were taller, bipedal, long legs and great travellers - changes in hominid hand structure = skilled use of tools - changes in tooth structure and massive reduction of jaw size = more varied diet - brain greatly evolved in size, increasing to more than 3 times its original volume Species Comparison - Descartes: human mind is special and separate from body and brain - Dualists: also rely on observation that human behaviour is more complex than other animals - Dualists believe human neuroanatomy and cognitive processes differ fundamentally from those of other animals Why Study Nonhuman Animals? - comparative studies show human brain and behaviour are different from other animals, but there are many similarities as well that can help shed light on human evolution - ex. similarities between humans and chimps- physical stature, facial features and expressions, brain similar in appearance and structure (humans is bigger), and have behavioural traits in common (social living, tool use and omnivorous foraging) - even comparisons with distantly related species (rats, cats & fruit flies) is informative - rat brain is like human brain and cortical functions in lab rats is remarkably similar to that of humans - slugs useful for studying how neurons interconnect to produce behaviour b/c their nervous system is relatively simple - fruit flies useful for studying genetic basis of behaviour b/c many generations of flies with nervous system alterations can be bred quickly in labs - genes: functional units that control the transmission and expression of traits from one generation to the next - studying other species makes important contribution to human brain-behaviour relations - brain-behaviour comparisons across species provide info that is difficult to obtain from studying a single species, even one as interesting as humans - differences between brains and behaviours of different species are as informative as similarities - ex. brains of birds is similar to mammals but arrangement of structures is different, they have no cerebral cortex - rodents closest order to primates but their brain has large olfactory bulbs and small cerebral cortex, opposite of primate brain PSY295 Chapter 2: Origins of the Human Brain and Behaviour Questions Addressed by Studying Nonhuman Animals 3 primary lines of research drive neuropsychological investigations with animals: 1) Understanding Brain Mechanisms - cross-species comparisons in neuropsychology are designed to arrive at an understanding of basic mechanisms of brain function- ex. vision - fruit flies and mammals have eyes with little in common and difference taken as evidence that eye evolved a number of times - but results from studies of genes responsible for encoding info about how eye will develop in various species show that same genes are implicated in all species - gene, Pax responsible for eye development in all seeing animals, demonstrating a much closer relation among diverse animals than previously thought - homeobox genes dictate body segment formation in both fruit flies and humans - difference in structure of eye and nervous system in different species are products of slight alterations called mutations, in genes and in the way they interact with the products of other genes 2) Designing Animal Models nd - 2 goal of comparative research is to design animal models of human neurological disorders - researchers want to produce disorder in animals, manipulate multiple variables to understand its cause and ultimately formulate a treatment - ex. Parkinson’s disease associated with aging in humans, whose symptoms are: rigidity that impedes voluntary movement, balance problems and tremors of head, hands and limbs - cause of disease is unknown and there is no cure - 3 goals in finding treatments: prevent disease, slow its progression once it has developed and treat symptoms as disease progresses - Parkinson models developed in rats, mouse and monkeys - major symptomatic treatment is drug, L-dopa, developed by studying rats 3) Describing Evolutionary Adaptations - study of evolutionary development of human brain is important to understanding what humans are - comparative research on how mammalian brain and behaviour evolved progresses in 3 ways: 1. Experiments mammals permit inferences about how environment in which species lived shaped its evolution, brain and behaviour. All mammal species evolved independently from some common ancestor 2. B/c mammalian species are related, commonalities tell us what humans inherited in common with other mammals, especially with species in our own primate lineage 3. differences in brains and behaviours of different species are insight into how species and individual differences arose - evolution & elaboration of human cerebellum associated with development of tool use PSY295 Chapter 2: Origins of the Human Brain and Behaviour Use of a Quasi-evolutionary Sequence - to conduct comparative investigations from a phylogenetic perspective, researchers choose species that constitute what Hodos and Campbell term a quasi-evolutionary sequence, a hypothetical sequence of animals that represent consecutive stages in evolutionary history - some cases animal chosen b/c it is the living descendant of extinct ancestor - evolutionarily older present- day animals resemble a common ancestor closely enough to stand for it - ex. present-day chimp close enough to common ancestor of chimps and humans to stand for that common ancestor - in quasi-evolutionary sequence for primate lineage, comparison of the brains and behaviours of the animals in the sequence reveals correspondence between new structural development and new behaviours - trees shrews’ striate cortex(primary visual cortex) = inherit our massive striate cortex - large temporal lobe in bush baby = excellent human memory - large frontal lobe in rhesus monkey = complex social life of humans - large parietal lobe in humans correlated with our ability to perform skilled movements required in tool making - evolution of new brain features in living primates explains evolution of brain and behaviour in humans Human Origins - knowledge of human origins began with Darwin’s publication of On the Origin of Species by Means of Natural Selection and The Descent of Man - speciation occurred rapidly in hominid lineage Hominid Evolution - evolution of humans from an ape ancestor to Homo sapiens is not linear - hominid family tree is a bush: for most of its history, many family members were alive at the same time - our species only surviving member, sitting alone on last living hominid branch - 3 lines of research through which scientists attempt to reconstruct story of human evolution are: 1) Archaeological Research - using ages of sediments within which bones of different hominids are found, archaeologists have created a lineage of hominid species that includes their approximate time of origin - skull casts sources of insight into brain structure - examination of habitat in which hominids lived and tools they used can be sources of insight into their behaviour - by using morphological reconstruction, for example investigators can approximate appearance of a hominid body, often from only skeletal remains, to reveal similarities and differences between hominids and us - Neanderthal, hominid species related to modern humans, lived in Europe, but disappeared 40,000 years ago PSY295 Chapter 2: Origins of the Human Brain and Behaviour - Neanderthals= same tool use, lived in family groups, made music & buried dead 2) Biochemical and Genetic Research - amino acid sequence of a cellular protein in one species can be compared with amino acid sequence of same protein in another species - change in one amino acid occur on average once every million years, and so differences between proteins provide a molecular clock that can be used to compare ages of different species - relatedness of different species can be determined by comparing DNA (deoxyribonucleic acid), the genetic material in the nucleus of the cell - genes are segments of DNA that specify what proteins a cell should make - gene is long chain of 4 kinds of nucleotide bases - through mutations, sequence of bases change to some extent and still leave a functional gene humans and chimps have 99% genes in common, each others closest living relatives - as progress in describing genome, full set of genes of a species, improves, an ideal description of human evolution would include information on w
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