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Chapter 2

PSYB65 Chapter 2.doc

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University of Toronto St. George
Zachariah Campbell

PSYB65 – Chapter 2 Species Comparison: - Cladogram – a graph that shows the relative time of origin of various closely related groups o Each branch point distinguishes animals positioned before that time point from animals positioned after it by one or more physical or behavioural traits. Why Study Nonhuman Animals? - Kanzi – revealed many similarities between humans and animals that can shed light on human evolution o The brains of both humans and chimpanzees are very similar in appearance and in structure, but chimpanzee brain is smaller o They both have behavioural traits in common, including social living, tool use and omnivorous foraging - Researchers also find comparisons with more distantly related species as well o Rat brains and their cortical function are similar to human brain o Slugs are useful for studying how neurons interconnect to produce behaviour because their nervous system is simple o Fruit flies are useful for studying the genetic basis of behaviour - Genes – the functional units that control the transmission and expression of traits from one generation to the next - Differences between the brains and behaviours of different animal species are as informative as their similarities o Cerebral cortex, is the most imposing feature of the mammalian brain o In terrestrial mammals, the cortical structures associated with the olfactory bulbs are the hippocampus in the temporal lobe, that takes part in memory Questions Addressed by Studying Nonhuman Animals: - 3 primary lines of research drive neuropsychological investigations with animals: o Understanding basic brain mechanisms o Designing animal models of human neurological disorders o Describing the phylogenetic (evolutionary) development of the brain Understanding Brain Mechanisms: - Cross-species comparisons in neuropsychology are designed to understanding the basic mechanisms of brain function - Claudia Hetzer-Egger – a gene called Pax, is responsible for eye development in all seeing animals, demonstrating a much closer relationship among very diverse kinds of animals - Homeobox genes – similar genes, dictate body segmentation in both fruit flies and humans - Mutations – slight alterations that produce, for example, differences in structure of the eye and nervous system in different animals Designing Animal Models: - Research animals substitute for humans because similar principles are assumed to underlie the emergence and treatment of a disorder in humans and nonhumans alike. o Ex. Parkinson’s disease – Symptoms include rigidity that impedes voluntary movement, balance problems, tremors of the head, hands and limbs. - Scientists have 3 goals in funding treatments: o To prevent the disease o Slow its progression once it has developed o Treat symptoms as the disease progresses - Parkinson models have been developed in the mouse, rat and monkey o A major symptomatic treatment developed by studying rats with a similar form of this disease was the drug, L-dopa Describing Evolutionary Adaptations: - Comparative research on how the mammalian brain and behaviour evolved progresses in 3 ways: o Experiments with other mammals permit inferences about how the environment shaped its evolution, brain and behaviour.  All mammalian species evolved independently from some common ancestor o Since mammalian species are related, commonalities tell us what humans inherited in common with other mammals o Differences in the brains and behaviours of different species are sources of insight into how species and individuals arose - A salient attribute of modern humans is tool use o Found both in living humans, extinct predecessors, and other species Use of a Quasi-evolutionary Sequence: - Quasi-evolutionary sequence – a hypothetical sequence of animals that represent consecutive stages in evolutionary history o When constructed for the primate lineage, a comparison of the brains and behaviours of the animals in the sequence reveals a correspondence between new structural developments and new behaviours  Ex. in tree shrews, presence of striate cortex (primary visual cortex) confers on shrews an ability to see branches, heights and insects.  This ability is not important to the grown-dwelling hedgehog, which represents an earlier stage in the sequence. - The evolution of new brain features in living primates explains the evolution of the brain and behaviour of humans - Michael Oldham and Daniel Geschwind – now using comparative genetic analysis of the quasi-evolutionary sequence of primates o To investigate the neural basis for the origins of language and other behaviours Human Origins: - Multi-cellular animals existed for 650 million years, mammals existed for 150 million years - Monkeylike mammals or primates existed for about 25 million years o Dozens of hominid species appeared and disappeared in the past 8 million years Hominid Evolution: - The evolution of humans from an ape ancestor to Homo sapiens is not linear o The hominid family tree is a bush, most of its history, family members were alive at the same time - 20,000-40,000 years ago, a number of human species coexisted, including modern humans, a new discovered species, Homo floresiensis - 3 general lines of research to reconstruct the story of human evolution are: o Archeological o Biochemical and genetic o Behavioural Archeological Research: - Archeologists have created a lineage of hominid species that includes their approximate time of origin o Skull casts are sources of insight into brain structure o Examination of the habitat in which these hominid species lived and the tools that they used can be sources of insight into their behaviour - By using morphological reconstruction, investigators can approximate the appearance of a hominid body o Often from only skeletal remains, to reveal similarities and differences between hominids and us - Neanderthal people used tools very similar to the tools used by Homo sapiens living at that time o They communicated by using language and held religious beliefs Biochemical and Genetic Research: - Evidence for rapid hominid speciation is supported by biochemical research o Amino acid sequence of a cellular protein in one species can be compared with the amino acid sequence of the same protein in another species o A change in amino acid may occur on average about once every million years  The differences between proteins provide a molecular clock that can be used to compare the ages of different species - Relatedness of different species can also be determined by comparing their DNA o Genes are segments of DNA that specify what proteins a cell should make  Through mutations, sequence of nucleotide bases can change o Genome – the full set of genes of a species  Improves an ideal description of human evolution Behavioural Research: - Comparative behavioural research yields evidence for theories about human evolution - Jane Goodall – Studies of chimpanzees paint a picture of a species very similar to humans o These animals have rich manual, facial and vocal communication capabilities, and they construct and use tools for defense and to obtain food and water Stages of Human Evolution: - Our family tree is bushy; representative species are shown disconnected rather than in a connected evolutionary sequence. o Behavioural changes in this sequence were associated with the increases in brain size - 4 general steps led from a chimpanzee-like common ancestor to modern humans, these steps were the evolution in hominids of: o An upright posture in which the hands were free o Extensive tool use o A traveling lifestyle o An elaborate culture Australopithecus: Upright Posture: - The ancestor of all hominids was an animal somewhat like Australopithecus (Southern ape) o These animals possessed a distinctly human characteristic: walking upright  Footprints feature a well-developed arch and big toe and point straight ahead, a pattern more like humans than apes o A reason for why the hominid lineage diverged from its ape ancestor could be due to climate change as an important evolutionary determinant - Yves Coppens – about 8 million years ago, a tectonic crisis (deformation of earth’s crust) left a wet jungle climate to the west and a much drier climate to the east o Caused no change to the apes in the west o Caused apes to evolve rapidly to survive in the mixture of trees and grass that formed their new brushwood habitat in the east. - Distinctive feature of the new hominids was a change in dentition that included a reduction in the size of the incisors and a flattening of the molars - Two versions of how the evolution of hominids took place o Down-from-trees hypothesis – proposes that the trees being farther apart required apes to adopt bipedal locomotion  Accompanying change in po
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