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Testing Natural Selection Orr 2009 presented the ways in which evolutionary genetics advancements solidified the validity of natural selection NS First looking into short life-span organisms is a must in enhancing ones knowledge about evolution by NS For example when a population of bacteria comprising of two genetic types was exposed to a sudden environmental change like an antibiotic the resistant and fitter type survived and reproduced more often whereas the non-resistant one was not as successful NS identifies the genetic types fitness differences and acts on the individual organisms level in this context the fitters genetic type frequency increased faster because its resistance was advantageous in this environment These and all other genetic types originate in mutations of DNA affecting organisms fitness which suggests the aforementioned adaptive evolution happened on the account of mutations and selection Furthermore molecular evolution could have resulted not only from adaptive but also neutral changes known as random genetic drift which is a key aspect in the neutral theory of molecular evolution Statistical tests determining the type of change and DNA sequence contribute greatly to illustrate the examination of gene divergence in two fruit fly species have supported the undeniable affective role of genetic drift but have found that NS overweighs all other probabilities responsible for the evolutionary divergence of most of the analyzed genes Additionally when large populations of small and fast procreating organisms were moved to a controlled environment and left to adapt biologists were able to examine the specific genes mutations increasing fitness on which NS acts and preserves Even though these tests cannot be used for simple organisms it is possible to apply them to higher organism found in their natural habitats The period of time for which they have diverged allows scientists to distinguish adaptive differences resulting from NS For instance a single gene UPI was found to be responsible for dissimilar colors and pollination in two related species of monkeyflowers Experimentation with hybrids
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