Coyne mentions as a little aside note on page 51 that the evolution of whales from land to water, as well as our evolution from the common ancestor with chimpanzees to humans today were 'remarkably fast.'
What do you think accounts for the speed of evolution? Why do some animals change and evolve faster than others? What factors could contribute to this? Is a quick reproduction rate the only reason for fast evolution to occur quickly? (Like in bacteria and flies, or flowers)
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A short generation does account for a factor of why some evolution is fast. For example, bacteria is the life time of a human can be seen evolving into a more resistant form to certain drugs and antibiotics. Aside from generation length, the environment also has some impact on evolution. As noted on p.132, the strength of the selection contributes to the rate of evolution. Jerry Coyne states that "if we are to see natural selection at all, it must be a strong selection, causing rapid change" (132). What this means is that if there is an environmental factor that immediately causes those who are not evolved/mutated to die, than the only survivors would be the new evolved versions. On the other hand, when the environmental stress is not directly preventing the unevolved version of a species from surviving, than those that are mutated/evolved would gain advantage and slowly beat out the regular ones in reproduction. In the case of bacteria, antibiotics are an immediate threat to the survival of the species, so we quickly prune out the regular versions and leave the mutated antibacterial resistant forms to survive and reproduce.
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ReplyDeleteI agree with Frank, in that the length of a generation is important in the speed of evolution. A number of factors contribute to how fast an organism changes, not in the least time or environmental pressure. I want to disagree partly with Michael's statement that environmental pressure is the strongest catalyst for rapid evolution - even if a lot of environmental pressure is exerted on a certain species, the species won't be able to evolve that quickly unless the lifespan of the species is fairly short. If the lifespan is not short enough for enough change to happen over a given amount of time, then the species will not evolve quickly, but instead be forced to move or die out, and possibly go extinct. This happened with several species, especially with the new arrival of more adaptable organisms. These foreign species out-competed native species, and some of the native species were unable to adapt or move out fast enough. On the other hand, environmental pressure is an important part of evolution, in addition to reproduction rate.
ReplyDeleteAnother factor would be how much the organism needs to change in order to be able to survive, or in order to progress. The more similarities two species share with each other, the more likely it is that these two species share a much closer common ancestor than two species that physically look very different. That's not to say that there aren't exceptions (just look at the monotremes - the echidna and the platypus certainly don't look too similar at a glance. Similarly, species that look similar could be separated by millions of years - convergent traits show this), but this method can usually be used in addition to more conclusive methods. As seen in Fig. 2 on page 8, humans and chimapnzees share many similar traits. Humans and chimpanzees are much closer in evolutionary terms than, say, salamanders and humans.
Environmental pressure is the strongest catalyst for rapid evolution. In the case of humans and whales, there was a lot of environmental pressure on their ancestors, and this caused rapid evolution. With regards to bacteria, antibiotics, an environmental pressure, force E. coli to evolve in order to combat the bacteria. Camouflage is also a defense mechanism that evolved in many mantid species. Campbell writes, "Related species of the insects called mantids have diverse shapes and colors that evolved in different environments" (Campbell 459). This camouflage clearly shows how environmental pressure forces organisms, in this case mantids, to evolve. Also, when looking at figure 22.12 in Campbell, one can clearly see how different species of mantids evolved to their specific environments. We studied defense mechanisms in the ecology and behavior unit this year. One of the defense mechanisms we looked was cryptic coloration, where an organism colors itself the same as their environment, such as the canyon tree frog (Campbell 1201). However, natural selection doesn't only occur when there is environmental pressure. During times of no environmental pressure, natural selection occurs in the form of stabilizing selection. Stabilizing selection prevents against extreme values of a trait, such as abnormally large or small babies. Also, I believe that fast reproduction isn't a reason for fast evolution, rather it is an advantage that allows an organism to evolve quickly. E. coli can reproduce very quickly. Campbell writes, "In a favorable environment, an E. coli cell can copy all [its] DNA and divide to form two genetically identical daughter cells in less than an hour" (Campbell 313). Because E. coli can reproduce so quickly, it can evolve quickly. As Frank mentioned earlier, bacteria evolve in order to develop resistance to antibiotics. However, quick reproduction is a means for quick evolution, not a reason for quick evolution. The idea of natural selection relates to the theme of continuity and change. Page 16 of the course outline book explains an example of continuity and change when it says "Changes in gene pools over time can be explained in part by natural selection for the fittest genotypes" (COB 16). Natural selection is a great example of continuity and change from an evolutionary standpoint.
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