Posted: Jun 20, 2010 4:22 am
@ susu.exp
Sorry, we seem to be discussing several things at once here. As I read it, Gould and Eldridge cam up with PE theory based on the fact that there are gaps in the fossil record. The traditional view was that the non-randomness of fossil preservation made it seem like there were gaps. Or that local extinctions were re-populated from refugia migrating into a region that had experienced some extinction event. Thus the transition seems "jerky"
Please bear with me, as I suspect I am being stupid. You defined PE as:
Surely the rates of morphological change are based on how when and where clades are able to adapt to environmental by playing with their [non-conserved] developmental gene complexes [or their upstream or downstream expression]. I think that this is highly germane to the discussion. An organism may look wildly different, but the underlying Bauplan is highly conservative. In mammals for example, the cervical vertebra number only seven, but humans and giraffes look very different. The genetic/molecular evidence thus has confirmed many homologies that anatomists have always known about, but by no means all. Thus you can have huge changes in morphology that is based on small [but important] changes in the Hox complexes. Thus fruit flies and humans look very different, yet at the genetic level, they share homologies.
So at the genetic level, it looks more like gradualism rather than PE. Further, these genetic changes seem to pre-date the appearance of morphological change as seen in the fossil record.
Many thanks for those, I have some reading to do!
Sorry, we seem to be discussing several things at once here. As I read it, Gould and Eldridge cam up with PE theory based on the fact that there are gaps in the fossil record. The traditional view was that the non-randomness of fossil preservation made it seem like there were gaps. Or that local extinctions were re-populated from refugia migrating into a region that had experienced some extinction event. Thus the transition seems "jerky"
Please bear with me, as I suspect I am being stupid. You defined PE as:
There are no "PE events". PE is a hypothesis about the distribution of rates of morphological change.
Surely the rates of morphological change are based on how when and where clades are able to adapt to environmental by playing with their [non-conserved] developmental gene complexes [or their upstream or downstream expression]. I think that this is highly germane to the discussion. An organism may look wildly different, but the underlying Bauplan is highly conservative. In mammals for example, the cervical vertebra number only seven, but humans and giraffes look very different. The genetic/molecular evidence thus has confirmed many homologies that anatomists have always known about, but by no means all. Thus you can have huge changes in morphology that is based on small [but important] changes in the Hox complexes. Thus fruit flies and humans look very different, yet at the genetic level, they share homologies.
So at the genetic level, it looks more like gradualism rather than PE. Further, these genetic changes seem to pre-date the appearance of morphological change as seen in the fossil record.
Citation for what? The MBL papers are
Raup et al. 1973 "Stochastic models of phylogeny and the evolution of diversity",The Journal of Geology, 81, 525-542.
Raup & Gould, 1974 "Stochastic Simulation and Evolution of Morphology-Towards a Nomothetic Paleontology" Systematic Zoology, 23, 305-322.
Schopf et al, 1975 "Genomic Versus Morphologic Rates of Evolution: Influence of Morphologic Complexity", Paleobiology, 1, 63-70.
Gould et al., 1975 "The Shape of Evolution: A Comparison of Real and Random Clades", Paleobiology, 3, 23-40.
If you want page numbers for the Structure, you´ll have to wait (don´t have it here, will check on Monday).
Many thanks for those, I have some reading to do!