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Author Topic:   Homologies versus Novelties, a false dichotomy?
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Message 1 of 2 (104591)
05-01-2004 5:03 PM

The basic question I have is if you can create two logically distinct categories about traits that have emerged as either an alteration of an existing trait (idea behind homologous traits) or emergence of strikingly novel adaptations?

I know at root every trait that has evolved is essentially an alteration of another trait but there seems to be, at least on the surface, a difference between how an arm and hand evolved from previous structures and the appearance of say feathers which were a truly novel adaptation.

The novel end of things comes out when the start of a trait first appears. The evolution of the nervous system from simple radial system to giant CNS system with a big brain while spectacular in its own right is essentially modification of a system that is in existence. To me this is different than the creation of the nervous system itself. I have seen it argued several times that the conservation of traits in the nervous system of animals suggest that it initially arose in a very small or even a single species which then diversified. This chance development of a system to send information between cells through electrical impulses obviously was a highly successful approach but is the development of this novel system able to be reduced to alterations of existing structures? Is the initial creation of the nervous system the same basic process as the evolutionary alterations and development of the existing nervous system into the range we see today?

There seems to be some sense of arbitrariness to the initial development of a trait as if a bunch of stuff is sort of thrown out, natural selection rids anything with a negative input and you are left with a range of traits that then evolve into the specific functions for the environment the organism is in. To say this in terms of my nervous system example, the way in which cells could choose to communicate could be nearly infinite. But a given species happened to develop a specific way that worked, since this species can then take over the niches that this communication system allowed it an advantage in it drives out any other arbitrary systems that developed after it. Since it was the only system left that was what natural selection “worked” with and what all animals with a nervous system developed from.

The same idea could be applied to any range of evolutionary “problems.” As organisms try to enter new environments they are faced with new challenges the solution to these problems could be infinite and the one chosen is basically arbitrary in the sense that what ever developed first and worked took over the new niche. Once the trait was there it would be altered for specific function.

So do you think there is something different going on between these two types of trait development or is this a false dichotomy?

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Message 2 of 2 (104650)
05-01-2004 10:01 PM

Thread moved here from the Proposed New Topics forum.

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