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Chapter 3

Chapter 3 – Evolution.docx

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Steve Joordens

Chapter 3 – Evolution, Heredity and Behaviour Case study: There was a pilot who transports sick patients to the hospital his name was Martin Hartwell. The plane crashed and two of the patients died but the pilot and a body named David (suffered from appendicitis) survived. However the pilot was unable to walk because he suffered multiple fractures. David helped the pilot survive by gathering food and such and died after 20 days. 12 days after David’s death the pilot was found and rescued. Charles Darwin  Darwin proposed the idea of biological evolution … the notion that populations of organisms change over time (physically and behaviourally) in a manner that ends up making them better adapted 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 (2) proximate causes - immediate environmental variables that effect behaviour Charles Darwin collected many species (finches and tortoise of Galapagos Islands) of animals during his voyage on the “Beagle” and sent many of the specimens back to England for later study he was fascinated by how well animals and plants seemed adapted to their environment and he also became interested in artificial selection … a procedure by which certain animals are mated to produce offspring with desirable characteristics (like breeding certain dogs) Natural selection 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 While “survival of the fittest” is part of evolution theory … fitness is defined in terms of reproductive success, which is measured by 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 As a species we are somewhat “out of control”. Our strong evolutionary success can be linked to two events: 1) Bipedialism - frees the hands so that he could hold things (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, and language too! Due to eating meat. 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 organism’s physical and behavioural makeup Related to this is the issue of heredity, the sum of the traits and tendencies inherited from one’s parents, grandparents, and so on DNA (deoxyribonucleic acid) is in the form of a twisted ladder (double bonded helix), with the sugar and phosphate forming the sides, and the four types of nucleotide (adenine, thymine, cytosine, and guanine) forming the rings Genes are located on chromosomes, and each chromosome contains a different sequence of genes We inherit 23 chromosomes from each of our parents, giving us 23 pairs. Different pairs control different things, for example one pair determines gender characteristics Sexual reproduction involves the union of a sperm and an ova … each of which are formed through a special form of cell division called meiosis Meiosis is a form of cell division by which sperm and ova are formed. The 23 pairs of
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