[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Who says dromaeosaurs can't fly?

At 11:31 PM -0400 9/12/02, Ronald Orenstein wrote:

Umm - I still don't see this. All cladistics does is produce a phylogenetic tree based on coded characters. It says absolutely nothing about when, or how many times, flight evolved. I don't see why you need to change the cladistically-derived tree at all based on flight or non-flight, as long as you are willing to assume that flight evolved within the maniraptorian complex more than once, or that it evolved more basally on the tree and was lost several times in the various cladistic branches. Where is the contradiction?

I think the problem may be that cladistics implicitly assumes that a character should have evolved only once -- not many times as you suggest. As I understand it, this is the base of creating a "most parsimonious" tree that is considered the most plausible one.

It's a problem because developmental genetics is showing that a lot of major traits are controlled by two genetic switches. One gene turns on a second gene -- that is, one gene controls whether or not a second gene will be expressed, and that second gene controls (for example) limb development. We have only a very primitive understanding of that process at present, but it's central the emerging discipline of Evo-Devo -- evolutionary development.

I don't understand the details, and I suspect a LOT remains to be learned. But just as it makes genetics a lot more complicated than the simple mendelian model, it also suggests evolutionary lineages can be very complex. -- Jeff Hecht