Chapter 2&3 Notes.pdf

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University of Toronto Scarborough
Zachariah Campbell

PSYB65Chapter 23 NotesChapter 2 Origins of the Human Brain and BehaviourCladogram a 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 Hominids our humanlike ancestors diverged from this ancestral ape lineage by acquiring characteristics that distinguished them from other apes Hominids were taller and there was less difference in height between males and females They were bipedal had long legs and were such great travelers that their descendants have populated every habitable continent Genes are the functional units that control the transmission and expression of traits from one generation to the next According to Claudia Hetzer Egger and coworkers a gene called Pax is responsible for eye development in all seeing animals demonstrating a much closer relationship among very diverse kinds of animals than had been suspected previously Similar genes called homeobox genes dictate body segmentation in both fruit flies and humans Thus segmentation of the human nervous system into the spinal cord brainstem and forebrain is produced by genes first discovered in fruit flies The differences in the structure of the eye and the nervous system in different animal species are the products of slight alterations called mutations in genes such as Pax and in the way in which the products of those genes interact with the products of other genes Parkinsons disease is associated with aging in humans and can affect as many as 1 of the population older than 65 years of age The symptoms include rigidity that impedes voluntary movement balance problems and tremors of the head hands and limbs The cause of Parkinsons disease is unknown however and there is no cure Quasi evolutionary sequence a hypothetical sequence of animals that represent consecutive stages in evolutionary history In some cases an animal can be chosen because it is the living descendant of an extinct ancestor The three general lines of research through which scientists attempt to reconstruct the story of human evolution are archaeological biochemical and genetic and behavioural The relatedness of different species can also be determined by comparing their deoxyribonucleic acid DNA the genetic material in the nucleus of the cell Genes are segments of DNA that specify what proteins a cell should make Each gene is a long chain of four kinds of nucleotide bases Through mutations the sequence of bases can change to some extent and still leave a functional gene As progress in describing the genome the full set of genes of a species improves an ideal description of human evolution would include information on what genetic modifications led to the evolution of modern humans Investigators agree that four general steps led from a chimpanzee like common ancestor to modern humans These steps were the evolution in hominids of1 An upright posture in which the hands were free2 Extensive tool use3 A traveling life style and4 An elaborate culture Two versions of how the evolution of hominids took place vie for prominence The down from trees hypothesis proposes that the trees being farther apart required apes to adopt bipedal locomotion The accompanying change in posture reduced the area of the body exposed to the sun and permitted the loss of body hair The water baby hypothesis proposed by Alister Hardy suggests a different order of events beginning with a hypothetical naked ape swimming and foraging on ocean beaches and later forced to abandon its semiaquatic habitat when the ocean receded In this scenario the animal is described as finding bipedalism and lack of body hair advantageous in swimming it then retains these features when it adapts to the land the Encephalization quotientEQ for mammals the ratio of actual brain size to expected brain size Expected brain size is based on an average for living mammals that takes body size into account This increase in brain size was due to two changes1 member species in the hominid lineage were becoming larger and2 their brains were becoming larger Neoteny the rate of maturation slows down enough that some juvenile features of predecessor species become the adult features of descendant species Many features of the human anatomy resemble juvenile stages of other primates a small face a vaulted cranium and a large brain to body size ratio an unrotated big toe upright posture and primary distribution of hair on the head armpits and pubic areas The typical mammalian cortex can be divided into areas that are specialized for movement body senses audition vision and olfaction In general the frontal movement parietal body senses temporalaudition and occipitalvision lobes subserve these functions in humans At least three factors determine cortical size absolute increases in size the addition of new skills and the relative changes in sensory and motor abilities Nineteenth century investigators attempted to correlate gross human brain size and behaviour with three questions in mind They asked whether brain size was related to1 a persons intelligence2 intelligence differences between sexes3 intelligence differences among nationalities and races
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