chapter 7

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Charles Darwin published On the Origin of Species by Means of Natural Selection. --> this is where he introduced the concepts of evolution and natural selection.

Darwin was the first to propose a mechanism to explain how species could evolve.

two important points come from his book.

modern species have descended from common ancestors (evolution)

natural selection is the mechanism of evolution

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The Mechanism of Natural Selection

overproduction & limited resources result in competition, and if the individuals of a population have variation, then natural selection will occur. this can lead to evolution if the beneficial variations are heritable.

overproduction - more individuals are born than can be supported by the environment

limited resources - the resources stay relatively constant

competition - more offspring are born than can be supported by limited resources

variation - no two individuals are alike

natural selection - those individuals with variations make them best suited to their environment will be more likely to survive and reproduce

heritability - the traits of an organism are passed on to the next generation

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individuals don't evolve.

natural selection works with heritable traits.

evolution does not have a goal.

individuals that enhance survival and reproduction will have more offspring.

adaptation is the accumulation of these favorable traits in a population over time.

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Evidence for Evolution

fossil record - organisms die and are compressed into rock

radiometric dating - determine age of fossil or position in the rock

transitional forms - evidence of change in lineages

biogeography - the geographic distribution of species

comparative anatomy - comparison of modern organism's body structure

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populations are the units of evolution.

natural selection acts on individuals, but evolution is defined only in terms of changes in a population over time.

darwinian fitness - the fittest individual does not always the strongest

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Mechanisms of Natural Selection

in addition to natural selection, there are other mechanisms that can also contribute to evolution in gene pools.

genetic drift - the change in a genes pool due to chance

bottle neck effect - population is reduced drastically in size

founder effect - few individuals migrate to a new isolated habitat

gene flow - genetic exchange among populations due to migration

sexual selection - is a form of natural selection that depends on an individual ability to obtain a mate

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Reproductive Barriers Between Species

behavioral isolation - members of a species often identify each other through specific rituals

mating time differences - many species are able to reproduce only at specific times

habitat isolation - if species live in slightly different habitats, they may never meet

mechanical incompatibility - members of different species can not mate together because their anatomies are different

gametic incompatibility - the gametes (sperm & egg) of different species usually can not fertilize each other

hybrid weakness - offspring of two species may be unfit, or they may be sterile

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Taxonomic Hierarchy

domain

kingdom

phylum

class

order

family

genus

species

general -----> specific

*Dumb King Pigott Came Over For Good Soup*