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- analogous to artificial selection in which breeder selects:
which individuals to reproduce
which individuals to die prematurely
- Darwin hypothesized a similar natural process, in which
some individuals have greater probability of reproduction
some individuals have lesser probability of surviving
- variation must exist in population
- variation must be genetically inherited
- variation must confer differences in fitness
predicted event if natural selection were to occur
- initially there is some frequency of mutant in population
- selection for mutant → frequency of mutant increases over time
- selection for wild-type → frequency of mutant decreases over time
- either way, relative frequencies of variants changes with time
- description of species changes! [called micro-evolution]
- data: there are cases where such changes have been observed
and probable selection mechanism has been identified
- therefore: micro-evolution occurs.
When sufficient changes occur between two populations, and a reproductive barrier develops
between the two populations, speciation, or the development of
a new species, should occur.
We do not hae any confirmation of this hypothesis, although several instances of
putative incipient speciation are being monitored with the
expectation that we will confirm it.
Some texts also use the term macro-evolution to describe evolution above the
species level. As you will learn in Principes of Biology 2, the taxa above the species
level are artificial, so it is less clear how contempory evolution theory should apply
to the taxa.
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