BL1006 DISCUSSION: study of natural selection

BL1006 DISCUSSION: study of natural selection
In this module, we continue our study of natural selection, the process by which the enormous diversity of life on Earth has evolved to become so wonderfully suited to the diverse number of roles available to living forms. Read through the entire post as students have found this additional information supportive of their understanding. Directions for your engagement are located at the end of the content.

In general, natural selection depends upon two assumptions: 1. A genetically diverse population. 2. A struggle for survival and mating in which the reproductive success of individual organisms depends on their genetic makeup.

If we assume these conditions hold, then we are considering a population in which the reproductive success of individuals is at least in part based on the genetic makeup of its individuals. This then implies the genetic makeup of a population will change over time. When the genetic pool of a population changes over time, then the population is evolving. Notice assumption #1 is pretty much guaranteed due to mutation.

Consider this simplified cartoon. In it, you can see how not only would tree height potentially select for taller giraffes but how giraffes would (over time) would select for more towering trees. Because individual giraffes realize they would do better to grow a longer neck and can do so, or because trees recognize they will survive better if taller, natural selection works on population genetics from generation to generation. Giraffes drive tree populations to become taller because they kill off the shorter trees. It is more difficult for short-necked giraffes to feed which leads to longer necked giraffes reproducing more and their genes spreading in the population. Incidentally, this is an example of coevolution. In general, evolution usually involves interactions between one or more species co-evolving together over evolutionary time.

BL1006 DISCUSSION: study of natural selection
Sometimes critics of Evolutionary Theory will suggest evolution is a random process and, therefore, could not possibly account for the extraordinary diversity and complexity of the living world. However, evolution via natural selection is not a random process, although it does have a relatively random component, mutation.

The random component of evolution is mutation. We know of many things that will increase the likelihood of a mutation occurring in a life form (mutagenic chemicals, exposure to UV and X-Ray radiation, etc.). We can never predict with certainty if a given organism will or will not have a mutation or what kind of a mutation it will have. For instance, there is a lot of strong evidence demonstrating smoking tobacco regularly will increase a person\’s likelihood of developing mutations and potentially cancer in lung tissues. However, we cannot say for sure if any given smoker or non-smoker develops such lung cancer. This aspect of evolution is thought of as random.

However, as you read this week, evolution is more about how mutations get either promoted or rejected in a population over time. Those mutations provide an individual with an advantage translating to more viable offspring becoming prevalent in a population. Those mutations inhibit reducing the likelihood an organism will have successful offspring becoming less popular in a population. Over time the population will evolve as a result.

An analogy might be a TV news show featuring a gambler for Las Vegas. If the gambler was not successful, they would not likely be featured in the new show. However, if the gambler just won a jackpot, the chances of being featured in the new show are much more significant. Thus, the actual gambling process (like mutation) might be entirely random (say with slots), but who gets featured in the news (like who is reproductively successful) is not at all unexpected. Does this make sense? Other thoughts or questions?

Other thoughts on this? Can you imagine a population in which reproductive success does not, at least in part, depend upon genetics? What would be necessary to have a population that does not evolve under the action of natural selection?

Please do respond after you have reviewed some of the material. What are your thoughts on evolution? Does any of this information create further interest for you? Be sure to comment on one or more of the topics.

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