In the Chapter "What about now?" Mr. Coyne brings up how lactose intolerance has arisen in different human populations. He cites this trait as evidence of "gene-culture coevolution" (218). In other words, a cultural change influences the development of an evolutionary trait. In this case, the raising of cows (cultural change) produced the new evolutionary opportunity to adapt the lactose tolerance gene and obtain a new source of food. Can you think of other examples of gene culture coevolution in a human population? Consult outside sources for guidance. Also, how does the concept of gene-culture coevolution relate to the theme of evolution or the theme of continuity and change?
Furthermore, reflecting back to past units on gene mutations and its relation to evolution, would you say that we are still evolving in a useful way? In other words, are we still influenced by natural selection to adapt in a way that allows for the prolongation of the human species? Or has the proliferation of human technology/influence eliminated the need for natural selection?
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One example of gene-culture coevolution is the development of advanced vocal cords in early human species. In the populations of other non-human primates, speech and facial communication wasn’t nearly as important as it was to early humans. According to this source(http://www.umass.edu/preferen/gintis/GeneCulture.pdf), “communication in other primates, lacking as they are in cumulative culture, goes little beyond simple calling and gesturing capacities”. So, as the culture of humans began to change and speech and communication became more important, humans changed genetically in order to communicate better. Evidence suggests that in early humans, more nerves and muscles developed in the mouth, and both the larynx and the tongue became more advanced. These changes better adapt humans for speech. Moreover, current humans have a low laryngeal placement, which “allows the throat to serve as a resonating chamber capable of a great number of sounds”. The lower laryngeal placement was first seen in the Homo heidelbergensis, an early hominid; Early hominids also developed a short oral cavity which helps in the production of consonants, whereas primates have long oral cavities. There are numerous other adaptations that illustrate my point, such as the muscles attaching to the face to allow the face to show emotions. (All of the above info comes from that link above). Clearly, as the culture of early hominids changed, humans adapted and were better able to communicate. This gene-culture coevolution relates to the theme of structure and function. The structural makeup of the throat and face evolution so as to function better in society(in this case, talk and make facial expressions). Gene-culture coevolution obviously relates to the theme of evolution because the development of these adaptations increased the evolutionary success of humans. Gene-culture coevolution can also relate to the biological theme of continuity and change because while early humans underwent drastic changes, there were still plenty of species of primates whose genes weren’t affected because there wasn’t really a need for these primates to gain more advanced ways of communication.
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ReplyDeleteTo answer the question of are we still evolving, Coyne notes on page 218 that there isn’t exactly a definitive answer. In general, I would say that we are not evolving in a way that would prolong the life of the human race. Clearly, technology has certainly counteracted natural selection in some ways. For example, in human societies thousands of years ago, having bad eyes might have drastically decreased one’s chance for survival. Those with the bad eye genes would die, and the amount of organisms with bad eyes would decrease because the bad eye genes become less and less common. Now, that entire process can be stopped by merely wearing a pair of glasses. Coyne’s most important point on this topic is that, as long as humans die before they stop reproducing, natural selection may be able to improve us. He also notes that diseases that kill after a human stops reproducing(such as diabetes and heart disease) might not be influenced by natural selection because the changes natural selection would make would not increase the humans’ reproduction rates. In the U.S., the reasons that people would die before finishing reproduction are not natural causes. Natural selection can’t do anything about the fact that guns kill millions each year. No genetic mutation is going to develop that would somehow make humans resistant to bullets. Given that natural selection of humans must mostly occur because of death that occurs before the finishing of reproduction, and that most causes of death before the finishing of reproduction(such as violence) cannot be changed by natural selection, then humans in the U.S. are evolving very little, if at all. The situation is different in Africa because there is a high rate of child mortality due to various diseases. Unlike guns, natural selection can work against diseases. For example, On page 219 Coyne mentions the CCR5-(delta)32 gene that protects against AIDS. That mutated gene will then be spread to offspring of the people with the gene, and then hopefully AIDS won’t be as deadly. So overall, evolution is probably helping to prolong the human species in places like Africa, but in more developed areas(i.e. The rest of the world), I think evolution isn’t occurring like as often as it has in the past.