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One of the fundamental facts in the world today is that positive natural selection has been a critical force in shaping the human genome. According to Marks, Positive natural selection has been defined as the process by which advantageous traits become more common in a population (1995). In this sense, these traits help the survival mechanism of an organism by increases the chances of survival and reproduction. The process of identifying such genes and traits in organism is one of the major cornerstones in the current efforts to dissect the biological history of the human species. The human genome has been identified as one of the most significant places where positive natural selection leaves distinctive signals in terms of evolutional progress. Apparently, it was perceived that over a hundred genomic regions are subject to positive natural selection and evolutional change in humans. However, recent studies show that it is only a handful of these regions that experience precise genetic changes.
The method that was originally identified as evolution by Charles Darwin is as a result of the propagation of advantageous mutations through natural selection. “However, in the last half century there has been considerable debate as to whether evolutionary changes at the molecular level are largely driven by natural selection or random genetic drift” (Baur & Lenz, 1931). This has brought many scientific analysts to try and identify the forces that drive evolutionary changes. The great breakthroughs with respect to human health have particularly been triggered by the fact that it is now possible to identify specific regions in human genome that show evidence of adaptive evolution. There are various regions in human genome that show evidence of adaptive evolution including;
Disease genes: According to a research carried out by Bakewell in 2007, an estimated 9.7% of positively selected genes were seen to be associated with diseases. This explains why some diseases in modern world can be adaptive. According to Yang & Bielawski, an example of one such disease is schizophrenia has been linked with increased creativity perhaps a useful trait for obtaining food or attracting mates in Paleolithic times (2000) Some other adaptive mutations have been found responsible for the reduction of contraction of certain diseases. However, the second explanation for the reduction of contraction risk is seen as somehow inapplicable going by the fact that mutation rate in the human genome is relatively low hence selection would therefore be significantly weak.
Immune genes: There are over four hundred and seventeen genes that have been found to be selectively adapted. “One of the explanations behind this is that immune genes are somehow involved in co evolutionary arms race with bacteria and viruses” (Zhang & Lee, 2005). These pathogens have been found to evolve very quickly which implies that the selection pressures change in a very rapid manner hence are able to give more opportunities to adaptive evolution.
Testes genes: Over two hundred and forty seven genes in the testes showed significant evidence of adaptive evolution according to a study carried out by Nielson in 2005. The main reason behind this was found to be partly as a result of sexual antagonism. This is because, male female competition in most occurrences facilitate an arms race of adaptive selection. Going by this, it is expected that women have more adaptive selection activities in their sexual organs. However, this is not the case according to research. However, sperm competition seems to be the best possible explanation behind the behavior of these genes.
Olfactory genes: Genes that are involved in detecting smell have over the years showed evidence of adaptive evolution. This is perhaps due to the fact that the smells that are encountered by humans are slightly different form what was being encountered in the past. This is withstanding the factor that human sense of smell has played an important role in determining the safety of food sources.
Nutrition genes: Adaptive selection is commonly seen in genes involved in lactose metabolism. This implies that a mutation linked to lactase persistence would in one way or another show very strong evidences of adaptive evolution.
Other: there are various other genes that show various evidence of adaptive selection including both the x and the y chromosomes.
The rate of adaptive evolution in the human genetic mechanism has over the years been perceived to be constant. It was estimated that 35% of adaptive selection is responsible for one adaptive substitution in the human lineage every 200 years since human divergence from old-world monkeys. This is going by the fact that the human population has grown significantly over time. This moreover reflects the theory that an increase in human population will lead to more adaptive substitutions. According to some analytical experts, cultural evolution may soon be replaced by genetic evolution which will then slow the rate of adaptive evolution in years to come. However, cultural evolution is also seen to have an effect on the rate of genetic adaptation going by the fact that cultural evolution has significantly increased communication and contact between different populations which provides genetic admixture between different populations.
This topic of evolutionary changes in the human genome is significantly related to physical Anthropology course in the sense that physical anthropology is an anthropology branch that studies the physical development in human species. This studies the evolution of human in relation to their interactions and physiological changes due to both internal and external factors. “There have been various attempts to correlate human physique with psychological traits such as intelligence, criminality and personality type, many of which proved themselves mistaken and are now obsolete” (Marks, 1995).