Tuesday, March 23, 2010

Adaptive changes Vs. Random changes

Coyne states that "natural selection is the cause of all adaptive evolution." (143) It is certain that most people believe that natural selection is the driving force of evolution. However, other drivers such as genetic drift, can also change the course of evolution. According to the reading and any biological thoughts, in what situations would the force of natural selection prevail? What situations would give an advantage to genetic drift? If there was a specie that can survive perfectly in any, and all environments, would genetic drift help that being in anyway or is selectively and artificially preserving genetic code the way to be?

1 comment:

  1. Natural selection is the process by which species adapt to their environment and in effect lead to evolutionary change. It occurs when individuals with certain characteristics have a greater survival or reproductive rate than other individuals in a population and hence they pass on these inheritable genetic characteristics to their offspring (actionbioscience.org). Putting it simply, it occurs when “the ‘good’ genes that lead to higher survival and reproduction will have relatively more copies than the ‘not so good’ genes”, and the weaker individuals are weeded out (Coyne 11). On the other hand, genetic drift is a change in the gene pool of a small population or organism that take strictly by chance. It can result in genetic traits being lost or widespread in a population without respect to the survival or reproductive value of the alleles involved. It “refers to the expected population dynamics of neutral alleles (those defined as having no positive or negative impact on reproductive fitness), which are predicted to eventually become fixed at zero or 100% frequency” (Sciencedaily.com).
    Genetic drift has to do with evolutionary change that is completely random and has nothing to do with adaptation. When compared to natural selection, it plays a minor role in the evolutionary theory because “it does not have the molding power of natural selection.” Natural selection, on the other hand, “always gets rid of harmful alleles and raises the frequencies of beneficial ones” (Coyne 123). Because of this, it is quite obvious that natural selection prevails in nearly all scenarios. Not only is it more common, but it also helps the individual survive and be more successful in its future generations. Genetic drift, however, can have the ability to overpower natural selection. For instance, especially in smaller populations, the sampling effect can be so large that it raises the frequency of harmful genes although natural selection is working in the opposite direction. This is the reason why there is a high incidence of genetically based diseased in isolated human communities, including Gaucher’s disease in northern Swedes, Tay-Sachs in the Cajuns of Louisiana, and retinitis pigmentosa in the inhabitants of the island of Trisitan da Cunha (Coyne 124). Nonetheless, genetic drift is referred to as “neutral” because it doesn’t intentionally do anything to help or hurt the individual. Overall, the relative importance of natural selection versus genetic drift in evolution remains a hot topic among biologists. Regardless of what role each play, one thing is for sure- they are the necessary forces that drive evolution forward.