hootmon writes:
In another thread”
Message 93”onfire stated the usual perception of how biological evolution occurs:
onfire writes:
There is no difference between micro and macro if you take into account transitional fossils.
There is no great leap from micro to macro, the whole arguement is wrong, transitional fossils, like that of the whales, shows
descent with modification. There is no need, in respect to the whale(and all other species), to have a micro/macro discusion. We classify them as different species giving them the appearence of a micro/macro change but they don't just change from one species to the next. The micro/macro debate is old, many transitional fossils have been found and the debate should have been put to rest, I see it hasn't.
But is "descent with modification" the only way biological evolution proceeds? Or can there be huge leaps of change occurring in biological evolution that do not follow the decent-with-modification rule? Could the former case be called "microevolution" and the latter "macroevolution"? And why does there always need to be a transitional fossil?
Of course, there does not always need to be a transitional fossil as so few species are ever represented by fossils at all. But descent with modification does require transitions, whether or not any were fossilized.
Thus, we have need to debate: "descent with modification" v. "larval hybridization." The former is well known for its role in the evolution of Darwin's finches, for example. The latter would engage more robustly the role of
horizontal gene transfer."
I am not sure I follow this. Horizontal gene transfer is a phenomenon well known among bacteria, but not frequent among eukaryotes. Is the hypothesis of larval hybridization intended to provide a mechanism of horizontal gene transfer in animals?
As a way to focus this discussion, I'll suggest that
the genetically free-wheeling affairs of larvae may account for incredible evolutionary leaps between taxa, leaving no evidence behind of descent with modification by way of transitional fossils.
I am not sure why this would be. We might approach the issue by asking first why does descent with modification require a period of transition.
Answer: because it takes time for a useful mutation to move from the one organism in which it originally occurs to every organism in the whole species.
How would horizontal gene transfer avoid this? Larval hybridization would only affect the individuals participating in the hybrid mating and their immediate offspring.
What comes next? Can these offspring still mate with their un-hybridized cousins? Is this the way they pass on their unique genetic pattern to other members of the species?
If this is the proposal, the only difference between normal descent with modification and larval hybridization is that ordinarily the modification begins as a change in the organisms own DNA, while with larval hybridization the modification is accomplished by the acquisition of DNA from another organism.
This sort of thing already happens in the cases of endogenous retroviral insertions. The new DNA is introduced by a retrovirus, but is then transmitted by inheritance in the usual way exactly as a mutation to the organisms own DNA is.
So how does this really differ from descent with modification? It seems it offers only an alternate mode of modification. It still relies on the transmission of that modification via descent. So it still falls within the category of descent with modification.
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