Comments

  1. Nerd of Redhead, Dances OM Trolls says

    The nerd in me wants to know why extra neck vertebrae causes cancer.

    If you were listening, PZ stated that the signals for the seven neck vertebrae were turned on at the same time as some anticancer genes. Either you have a seven vertebrae neck, or you are susceptible to cancer. For this to change, there needs to be a separation of timing of the turn on signals, which must also percolate through the general population, Not very likely. The evodevo genes must be very close and essentially intertwined.

  2. Bruce says

    Here’s my favorite analogy for this.
    Imagine photos of a busy city interstate highway with many lanes and cars completely filling it during rush hour.
    Now imagine some photos taken of it once every couple of minutes.
    When people who have never seen a city study these photos, they will see evidence of cars in lanes. But very rarely will they see any evidence of a transitional species of car going between two lanes. So a traffic creationist would suppose that god put all of those cars into their specific lanes, because they see no evidence of cars evolving to change lanes from one lane to another.
    The fossil record is like an instantaneous photo, where we are lucky to have similar views a few thousand years apart. It takes some sophisticated analysis for some to realize that cars can (and do) change lanes, and that, just because most cars are mostly staying in their lanes, that doesn’t prevent lane changing.
    So, how would we describe all of this.
    Cars are “in stasis” staying in their own lane. Then, in an instant relative to an hour-long drive, they are suddenly in a new lane, in stasis where they will stay in that lane for many miles. So punctuated equilibrium is a good description of cars driving in lanes and mostly staying in their lane, but every so often, one of them will change into a new lane, and then spend a long time staying in that lane. And with only fossils, like occasional photos, it is hard to see direct evidence of lane changing or punctuation or speciation as a new situation seems to suddenly develop, as the car in front of you seems to take tens of thousands of years to finish changing lanes.

  3. says

    PZ, as usual a very good summary of the evidence for punctuation as a pattern, and the developmental issues involved. When I taught about this I emphasized that there was a distinction between PE as a pattern and PE as an argument for separate processes. Your argument is fine for the issue of what the patterns are, and certainly the old view that evolution always shows us a slow smooth linear pattern of change was disposed of by Niles Eldredge and by Stephen Jay Gould (and Jack Sepkoski and David Raup and Steven Stanley) in the 1970s and 1980s.

    But I would point out that they also argued (as part of “PE”) that this showed that individual selection within species could not account for what was seen and that within-species individual selection was just doing uninteresting maintenance of stasis, and that the real mechanism of long-term change was species selection. Population geneticists and quantitative geneticists countered, in the 1980s, by giving examples of ways rapid individual selection could lead to the same pattern. Steve Gould waffled a bit after that, while Steve Stanley has remained hard-core. Things have been in relative stasis since then.

    There are really three arguments here: (1) what patterns do we see? (2) what levels of selection are involved? and (3) do we get to declare the Modern Synthesis dead and declare that we have come up with a new one? I’d prefer not to rename it but obviously that is mostly a matter of taste.

    (Sorry for the slow response, I hope I caught up with this thread in time),

  4. nomdeplume says

    Nice summary – so PE is much less than I thought it was. Seems to me the confusion has come from the general public’s idea of evolution as being “change in a population through time”. What is rarely considered is the other half of the process which is separation of populations geographically, that is the “origin of species”. If you have species in habitats which (a) change very little over time and (b) don’t provide geographical barriers, then they can remain essentially unchanging, apart from gradual drift or bottlenecks. If you have species in a varied and changing environment, with barriers which form and vanish frequently, then you will get a lot of new species and a lot of change. Is that all E & G were saying?

Leave a Reply