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How Humans Evolved Textbook Notes: Part 1 Chapter 1,2,3,4

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ANTH 203
Michael Bisson

How Humans Evolved Textbook Notes How Evolution Works PART 1Chapter 1 Animals and plants are adapted to their conditions Organisms are more than just suited to their environments they are complex machines made up of many exquisitely constructed components or adaptations that interact to help the organism survive and reproduceDarwins theory of adaptation o Follow 3 postulates 1 the struggle for existence 2 variation in fitness and 3 the inheritance of variation 1 The ability of a population to expand is infinite but the ability of an environment to support populations is always finite a Populations grow until they are checked by the dwindling supply of resources in the environmentb the struggle for existence 2 Organisms within populations vary and this variation affects the ability to survive and reproduce a Some individuals will posses traits that allow them to survive and reproduce more successfully3 This variation is transmitted from parents to offspring a If the advantageous traits are inherited by offspring then these traits will become more common in succeeding generationsNatural selection traits that confer advantages in survival and reproduction are retained in the population and traits that are disadvantageous disappear Darwins finches o Example of how natural selection produces adaptationso They were able to directly document how Darwins 3 postulates lead to evolutionary change Supply of food on the island was not sufficient to feed the entire population and many finches did not survive the drought population declinedBeak depth varied among the birds and affected the birds survivalObserved that birds with deeper beaks were able to process large seeds better than those with a shallow beakDuring the drought the relative abundance of small seeds decreased forcing shallow beaked birds to shift to large hard seedsAverage beak depth increased after the drought The average morphology of the bird population changed so that birds became better adapted to their environment Selection preserves the status quo when the most common type is the best adaptedEvolutionary theory predicts that over time selection will increase the average break depth in the population until the costs of larger than average beak size exceed the benefits o Finches with the average beak size are more likely to survive and reproduceo When beak size does not change we say that an equilibrium existso The process that produces this equilibrium state is called stabilizing selection Selection is required to change a population and required to keep a population the same Darwin a species is a dynamic population of individualsThe characteristics of a particular species will be static over a long period of time only if the most common type of individual is consistently favoured stabilizing selectionIndividual Selection Adaptation results from the competition among individuals not between entire populations or speciesSelection leads to changes in behaviour or morphology that increase the reproductive success of individuals but decrease the average reproductive success of the group population and speciesThe Evolution of Complex AdaptationsWhy Small Variations are Important Continuous Variation The distribution of heights in peopleDiscontinuous Variation A number of distinct types exist without any intermediatesComplex adaptations can arise through the accumulation of small random variations by natural selection Selection is a cumulative process because it can give rise to great complexity starting with small random variations Why Intermediate Steps are favoured by Selection Convergence the evolution of similar adaptations in unrelated groups of animals o Ex in South America a marsupial sabertoothed cat and the eyeChapter 2
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