Examples for the evidence for evolution often stems from direct observation of natural selection in the field and the laboratory. Scientists have observed and documented a multitude of events where natural selection is in action. The most well known examples are antibiotic resistance in the medical field along with better-known laboratory experiments documenting evolution's occurrence. Natural selection is tantamount to common descent in the fact that long-term occurrence and selection pressures can lead to the diversity of life on earth as found today. All adaptations—documented and undocumented changes concerned—are caused by natural selection (and a few other minor processes). The examples below are only a small fraction of the actual experiments and observations.
Antibiotic and pesticide resistance
The development and spread of antibiotic resistant bacteria, like the spread of pesticide resistant forms of plants and insects is evidence for evolution of species, and of change within species. Thus the appearance of vancomycin resistant Staphylococcus aureus, and the danger it poses to hospital patients is a direct result of evolution through natural selection. The rise of Shigella strains resistant to the synthetic antibiotic class of sulfonamides also demonstrates the generation of new information as an evolutionary process. Similarly, the appearance of DDT resistance in various forms of Anopheles mosquitoes, and the appearance of myxomatosis resistance in breeding rabbit populations in Australia, are all evidence of the existence of evolution in situations of evolutionary selection pressure in species in which generations occur rapidly.
E. coli long-term evolution experiment
Experimental evolution uses controlled experiments to test hypotheses and theories of evolution. In one early example, William Dallinger set up an experiment shortly before 1880, subjecting microbes to heat with the aim of forcing adaptive changes. His experiment ran for around seven years, and his published results were acclaimed, but he did not resume the experiment after the apparatus failed.
The E. coli long-term evolution experiment that began in 1988 under the leadership of Richard Lenski is still in progress, and has shown adaptations including the evolution of a strain of E. coli that was able to grow on citric acid in the growth media—a trait absent in all other known forms of E. Coli, including the initial strain.
Natural selection is observed in contemporary human populations, with recent findings demonstrating that the population at risk of the severe debilitating disease kuru has significant over-representation of an immune variant of the prion protein gene G127V versus non-immune alleles. Scientists postulate one of the reasons for the rapid selection of this genetic variant is the lethality of the disease in non-immune persons. Other reported evolutionary trends in other populations include a lengthening of the reproductive period, reduction in cholesterol levels, blood glucose and blood pressure.
Lactose intolerance in humans
Lactose intolerance is the inability to metabolize lactose, because of a lack of the required enzyme lactase in the digestive system. The normal mammalian condition is for the young of a species to experience reduced lactase production at the end of the weaning period (a species-specific length of time). In humans, in non-dairy consuming societies, lactase production usually drops about 90% during the first four years of life, although the exact drop over time varies widely. However, certain human populations have a mutation on chromosome 2 that eliminates the shutdown in lactase production, making it possible for members of these populations to continue consumption of raw milk and other fresh and fermented dairy products throughout their lives without difficulty. This appears to be an evolutionarily recent adaptation to dairy consumption, and has occurred independently in both northern Europe and east Africa in populations with a historically pastoral lifestyle
Nylon-eating bacteria are a strain of Flavobacterium that is capable of digesting certain byproducts of nylon 6 manufacture. There is scientific consensus that the capacity to synthesize nylonase most probably developed as a single-step mutation that survived because it improved the fitness of the bacteria possessing the mutation. This is seen as a good example of evolution through mutation and natural selection that has been observed as it occurs.
After General Electric dumped polychlorinated biphenyls (PCBs) in the Hudson River from 1947 through 1976, tomcods living in the river were found to have evolved an increased resistance to the compound's toxic effects. At first the tomcod population was devastated, but it recovered. Scientists identified the genetic mutation that conferred the resistance. The mutated form was present in 99 per cent of the surviving tomcods in the river, compared to fewer than 10 percent of the tomcods from other waters.
One classic example of adaptation in response to selection pressure is the case of the peppered moth. The color of the moth has gone from light to dark to light again over the course of a few hundred years due to the appearance and later disappearance of pollution from the Industrial Revolution in England.
Radiotrophic fungi are fungi that appear to use the pigment melanin to convert gamma radiation into chemical energy for growth and were first discovered in 2007 as black molds growing inside and around the Chernobyl Nuclear Power Plant. Research at the Albert Einstein College of Medicine showed that three melanin-containing fungi, Cladosporium sphaerospermum, Wangiella dermatitidis, and Cryptococcus neoformans, increased in biomass and accumulated acetate faster in an environment in which the radiation level was 500 times higher than in the normal environment.
Urban wildlife is wildlife that is able to live or thrive in urban environments. These types of environments can exert selection pressures on organism, often leading to new adaptations. For example, the weed Crepis sancta, found in France, has two types of seed, heavy and fluffy. The heavy ones land nearby to the parent plant, whereas fluffy seeds float further away on the wind. In urban environments, seeds that float far often land on infertile concrete. Within about 5–12 generations, the weed evolves to produce significantly heavier seeds than its rural relatives. Other examples of urban wildlife are rock pigeons and species of crows adapting to city environments around the world; African penguins in Simons Town; baboons in South Africa; and a variety of insects living in human habitations
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