Monday, March 9, 2009
Huxley vs. Darwin - Natural Selection
Biologist Thomas Huxley believed that natural selection took place on a bloc-by-bloc basis, essentially that evolution took place involving large discontinuous differences among individuals. How does this differ with natural selection proposed by Darwin? Which type of selection is correct? Why?
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Darwin's beliefs radiated from a central idea that evolution is a slow moving, gradual event. Huxley, on the other hand, had beliefs centered around the idea that evolution was a much more rapid process. Huxley's ideas were supported by the fact that there is a lack of fossil evidence that displays transitions of one form of an organism, to another. Instead of transitional forms, there seems to be fossils of only new species an old species of that same organism. Evidence for Darwin lies in the simple notion of the great amount of time that has taken place between us and our ancestors. It is this time that allows for a slow/gradual evolutionary process to take place. The matter over which type of evolutionary process is correct is subjective. I personally believe that Darwin's theory is more tangible in that that why there is such a huge variety of organisms today.
ReplyDeleteI think that Karthik makes a good point, but a clearer distinction exists. Huxley believed that change could only occur in large packages, like Mendelian Inheritance's idea of wrinkled versus round peas. However, Darwin's belief stated that there could be many intermediate steps between two states of being, as proved by the hooded mouse experiment. There were not two states (black-head only and full black-body) but several intermediate steps in between the latter and the former, thus proving that Evolution works through a gradient, and not through leaps and bounds.
ReplyDeleteI agree with the two former posts in saying that I think Darwin's theory seems to make more sense based on what we see in the amount of diversity in our world today.
ReplyDeleteHuxley's evidence of “rapid evolution" is only "proven" through his observation of extra digits on humans and animals that fully arose in one generation (45).
Meanwhile, Darwin was able to prove his theory of natural selection and the idea of gradual change through his study with breeding pigeons (44). Also the graph on page 53 shows the gradual change of the color of moths due to the improvement of air quality. When the conditions changed, the "favored" trait went from a dark color to the lighter color but the "evolution" of this trait occurred over 95 years, a long period of time, not over one generation.
Huxley's belief that natural selection acted on "Saltations" attempted to address to issues which can be resolved by Darwinian evolution: structural complexity and the quickness of evolution (45).
ReplyDeleteHuxley's ideas served as an expedient in answering the question of complexity, however it supported by little evidence. On the other hand, experimentally supported Darwinian evolution shows that complexity can arise in a gradual process since all organisms inherit a genetic organ building “tool kit” from their ancestors (194). For example, all organisms with eyes have the gene Pax-9 (italics) which is integral to the development of eyes.
Darwinian evolution also addresses the issue of how traits can evolve and be displayed by the majority of a population so quickly through the concept of compounding natural selection. As Carroll states, even if a trait provides a small advantage such that organisms with that trait produce 101 viable offspring compared to the 100 viable offspring of organisms without the trait, this advantage can quickly allow the trait to propagate through a large population. Indeed if the trait happened to be dominant, then it would increase in frequency from less than 1% of a population to greater than 90% in 3000 generations. 3000 generations isn’t very long relative to geological time, especially in the many species with generation times less than year long.
Darwinism is clearly more accurate the Huxley’s views because not only is Darwinism backed by evidence but Darwin’s ideas also address the issues with natural selection Huxley’s views set out to solve.