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Psychology (9,545)
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Chapter 3

Psych. Ch. 3

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University of Toronto Scarborough
Steve Joordens

Chapter 3 - Evolution, Heredity, and Behaviour Evolution Theory Darwin proposed the idea of biological evolution … the notion that populations of organisms change over time in a manner that ends up making them more suited to their environment. This has lead scientists in many areas (but especially biology and psychology) to consider the adaptive significance of the physical and behavioural characteristics of their subjects A distinction is often drawn between: (1) ultimate causes - events and conditions which, over generations, have shaped the behaviour of our species, versus (2) proximate causes - immediate environmental variables that effect behaviour Brief History of Darwin Collected many species of animals during his voyage on the “Beagle” and sent many of the specimens back to England for later study Was fascinated by how well animals and plants seemed adapted to their environment. Also became interested in artificial selection … a procedure by which certain animals are mated to produce offspring with desirable characteristics. Wondered if a similar process might also occur in nature … a natural selection Began collecting data to support his theory of natural selection … but did not publish his ideas or data for 20 years … until prompted by finding out that somebody named Wallace had a similar theory Published his ideas in a book called “Origin of the Species” … a best seller then, and now Premises of Evolution The 4 basic premises of Darwin’s theory of evolution 1) The plant and animal communities of the world are dynamic, constantly changing the physical and behavioural characteristics 2) Evolution is gradual. Changes arise through slow and steady environmental changes. Sudden changes challenge a species’ ability to adapt 3) All organisms descended from a single common ancestor. Over time, different species evolved, each adapted to their own ecological surroundings 4) Natural selection not only causes changes during changing environments, it also prevents changes during static environmental conditions Process of Natural Selection While “survival of the fittest” is part of evolution theory … fit does not mean physically fit. Rather fitness is defined in terms of reproductive success which is measured as the number of viable offspring an organism can produce relative to the organisms that it competes for resources with. Two processes affect changes to a species 1) Variation - individuals vary in terms of their physical and behavioural characteristics. This variation is often discussed in terms of differences in genotypes (an individuals genetic make-up) and phenotypes (an individuals physical characteristics and behaviour phenotypes are the result of the interaction between an organisms genotype and its environment 2) Competition - competition for food and mates is critical for insuring natural selection. If there were no competition, fitness would not matter Natural Selection in Human Evolution Does natural selection apply to humans as well as to other animals? There is now strong genetic evidence that we have a common with the gorillas and chimpanzees As a species we are somewhat “out of control”. Our strong evolutionary success can be linked to two events in our past: 1) Development of Bipedialism - thereby freeing up the hands for all sorts of mischief (e.g., tool making, weapons, building in general) 2) Encephalization of the Brain - The larger brain allowed more brain area to be expended on cognitive operations like thinking, reasoning, and decision making another important things it allows is planning … the ability to plan for and predict future events … oh, and language too! Genetics and Heredity -Darwin’s work lead the way to new fields of research including genetics, the examination of the structure and function of genes, including the manner in which genes are passed between generations -Included in this is the study of how genes affect an organisms physical and behavioural makeup -Related to this is the issue of heredity, the sum of the traits and
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