Evolution Case

Evolution can be defined as a genetic change in a population which can be the result of natural selection. The natural selection is determined by the individual organism that is born with characteristics that will enable them to survive and therefore produce more offspring than other individuals in their population (Phelan 2011). An example of evolution occurring within the past 200 years is the beak size of the medium ground finch which was documented between 1976-1978 by Peter and Rosemary Grant on the island of Daphne Major which is one of the Galapagos Islands on which Darwin also observed the finches (Weiner 1994). The finch has proven to be a very good example of natural selection leading to evolution. On the islands where the observations took place, there were 21 populations of finches with different sizes of beaks which made them exceptionally variable and meeting one of the conditions necessary for natural selection. The reason for natural selection occurring is that the size and shape of the birds' beaks had to mutate in order to eat larger seeds. This was documented by the Grants by the end of 1977 when a drought had finally ended on the island of Daphne Major. Meeting the condition of fitness is the fact that the beak size of the finches had increased after the drought. Since seeds had become scarce, the birds had to resort to eating the seeds of the caltrop, but they were hard to crack. The finches with the larger beaks were at an advantage and survived the drought because they were able to crack the seeds. Surprisingly, there were more male survivors after the drought because they are typically larger than females and have proportionately larger beaks. The result

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was an increase in beak size due to natural selection in favor of finches with larger beaks (Pond, Silvertown, and eta al 2008). It was noted later by the Grants that the smallest details of the birds, including the beak size and shape was passed on to the offsprings allowing them to pass the test of heritability – the last condition needed to meet the conditions for natural selection.

An example of human evolution taking place within the past 10,000 years is lactose tolerance. In the past, the human ability to digest lactose was turned off after weaning because the lactose enzyme was no longer needed. While many Americans take drinking milk for granted because it is so common, an interesting fact is that 10% of Americans, 50% of Spanish and 99% of Chinese are still lactose intolerant (Understanding Evolution 2012).

The genetic change for lactose tolerance in East Africans took place within the last 3000 years. The principal mutation is found in the ethnic groups of Kenya and Tanzania where archaeological evidence suggests the pastoral people lived 3000 to 7000 years ago (Wade 2012). The practice of raising dairy cattle eventually spread from Africa and the Middle East to Europe.