Answer:
a) individuals in a population vary
some traits are more favorable
more offspring are produced than can survive; (competition)
those individuals with favorable traits have an increased -reproduction rate which thereby increases the favorable traits in the population
b) Natural selection and the formation of insecticide-resistant insects or antibiotic-resistant bacteria :
bacteria are better fit to survive when compared to larger more complex organisms because they are quick to reproduce, thus allowing them to more quickly change and evolve. As antibiotics are released into the environment, mutations occurring in at least some bacteria within a population are likely to be resistant. Therefore, as the resistant bacteria survive and reproduce, the newly formed offspring will have acquired the resistant traits to the drug, thus making it no longer affective on the population.
Speciation and isolation :
During allopatric isolation, organisms of a species are separated into different populations (geographically separated) and gene flow is cut off, causing them to evolve to better fit their new niche. This evolution occurs over time, as the organisms better fit for the new environment survive and pass on their favored genes. Eventually, the changes in the DNA of the separated organisms will accumulate to form a new species, separate from the old one and better adapted to the environment. These new species will not be able to interbreed to form fertile offspring. In sympatric isolation, the organisms are "reproductively isolated", meaning the organisms still live in the same area but are still separated. Other forms of isolation are geographic isolation, ecological isolation, temporal isolation, behavioral isolation, mechanical isolation, and gametic isolation, which are all pre-zygotic. Post-zygotic isolations include reduced hybrid viability, reduced hybrid fertility, and hybrid breakdown. The two different types of rates of speciation are gradualism, which is a gradual accumulation of small changes over time, or punctuated equilibrium, which is rapid bursts of change mixed with long periods of little or no change.
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