Download 10.3 Natural Selection Variation of similar

10.3 Natural Selection
Variation of similar species among islands, fossil evidence, and geologic events convinced Darwin that evolution occurs. BUT he had yet to determine HOW evolution could happen.
Darwin spent 20 years conducting research, after his voyage, in attempt to understand HOW evolution occurs.
One of his biggest influences was the work of farmers and breeders.
­He noticed that domesticated species showed variations in their traits that did not show in their wild relatives.
Artificial Selection­ the process by which humans change a species by breeding it for certain traits.
­This makes use of the genetic variation in plants/animals
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To explore the idea of natural selection, Darwin turned to the hobby of breeding pidgeons. (He had no knowledge of genetics.)
­He realized that in order for artifical or natural selection to occur, traits had to be heritable.
Heritability ­ ability of a trait to be passed down from one generation to the next.
Darwin determined that in nature the environment creates the selective pressure, rather than humans, and that determines if a trait is passed down or not.
Natural Selection­ a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than other individuals. (a mechanism for change in a population)
­In nature characteristics are selected only if they give advantages or benefits to the organism.
­He also realized that 'perfect' individuals did not happen in one generation­­it took many generations to produce the variety.
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Thomas Malthus­ had previously proposed that resources such as food, water, and shelter were natural limits to population growth in humans.
­Darwin reasoned that a similar struggle took place in nature.
Population­ all the individuals of a species that live in a given area.
*Darwin also noted that on the Galapagos Islands some species were very well­suited to their environment but he figured that it had probably taken several generations to get to that point so he called this 'decent with modification'
­Charles Darwin and Alfred Russel Wallace both independently developed a theory to explain how evolution took place.
­Both had studied plants/animals in the tropics and the fossil recond
­Wallace wrote to Darwin and later they co­presented their ideas to a groups of scientists.
­Darwin is credited with the theory of natural selection because he was the first one to publish his ideas in his book, "The Origin of Species by Means of Natural Selection"
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4 Principles to the Theory of Natural Selection
1. VARIATION­ there is variety among individuals of the same species either inherited or from genetic mutations
2. OVERPRODUCTION­ lots of offspring gives greater chance that some will survive and it creates competition for resources.
3. ADAPTATION­ certain variations allow individuals to survive better thus 'naturally selecting them to live longer and produce more offspring
4. DESCENT WITH MODIFICATION­ over time natural selection results in species with adaptions that are well­
suited for survival and reproduction in an environment. fitness­ a measure of the ability to survive and produce more offspring relative to other members of the population in a given environment.
Natural selection acts on phenotypes ­ can only act on traits that already exist
­can not change the genetic material that can only change by genetic mutations
­As the environment changes, different traits become beneficial
Adaptive characteristics that are passed down over the generations does not mean that individuals will necessarily become perfectly suited to their environment ­some structures take on new functions.
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