Major evolutionary transitions

From: Keith B Miller (
Date: Thu Apr 19 2001 - 23:54:42 EDT

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    > Thanks for the update, Keith. You speak of the "range of environments" as if
    > it were an established fact. What are they? Wetlands? What else is there?
    > I would appreciate any references you have on these points. Moreover, so
    > what? If there were in fact a range of environments, would the animal not
    > stay in the one it was best adapted to and ignore the rest? Or are you
    > suggesting that these environments appeared sequentially and that the animal
    > was forced by necessity to adapt to the current one?

    Lets use the example of whale evolution. There are now 26 fossil species
    of primitive whales known that have been assigned to four families: the
    Pakicetidae, Ambuloceticae, Remingtonocetidae, and Protocetidae. These
    show a really amazing progression. Not only do the fossils occur in the
    correct chronological order, but they are found in progressively more
    marine settings. The most primitive group, the pakicetids, occur
    exclusively in river channel deposits. The ambulocetids and
    remingtonocetids are found in coastal and tidal deposits with freshwater
    influence. Early protocetids are associated with shallow nearshore
    environments. Not until the later fully marine-adapted protocetids are
    fossils found in clearly open marine deposits. These are also the first
    whales that would have been capable of worldwide dispersal, and they are
    indeed the first to be found outside Indo-Pakistan!

    The whales evolved after the extinction of the large marine reptiles. It
    is a repeated feature of the fossil record, that the extinction of animals
    occupying a particular ecological niche is followed by the radiation of
    another existing group into that vacated niche. This is the same pattern
    that is seen with the rapid radiation of placental mammal herbivores and
    carnivores following the extinction of the non-avian dinosaurs.

    Transitional aquatic/terrestrial environments provide settings for the
    evolution of features that are "preadapted for" either terrestrial or
    aquatic existence. The first limbs are now understood to have evolved as
    an adaptation for scrambling around in shallow water rather than as
    terrestrial adaptations. The first tetrapods had internal gills and were
    aquatic animals. However, once limbs appeared they provided a clear
    adaptation that enable their bearers to exploit a previously empty niche.

    > The flipper transition is only one of a whole host of others that had to be
    > coordinated to produce the whale from whatever its precursor was. You know
    > what these changes were and the magnitude of the problem of coordinating
    > them. But I don't believe you have addressed the problem. Do you really
    > believe that these coordinated changes were brought about by random mutations
    > (with respect to the future) selected by whatever environment, or genetic
    > drift, or any other undirected process?

    The whales are illustrative here. In addition to the reduction in limbs
    serval other skeletal changes occurred. For terrestrial animals the pelvis
    and shulder girdles must be firmly attached to the vertebral column in
    order to support the body against gravity. In water, the body is buoyant.
    In the fossil specimens the vertebral column is progressively detached from
    the limbs. In the early protocetids the pelvis was connected to the
    vertebral column by only a single vertebra. In later protocetids the
    pelvis was completely separated from the vertebral column. Associated with
    this is a progressive change in swimming from limb propulsion to tail

    For a similar account of turtle evolution see:

    Lee, M.S.Y., 1996, Correlated progression and the origin of turtles:
    Nature, vol. 379, p. 812-815.

    I find these changes to provide no particular unique challenge to
    evolutionary theory.

    Undirected in what sense? From within nature -that is, from a creaturely
    perspective - evolution is undirected. From a broader retrospective view -
    evolution does have direction. From a theological perspective - God is
    accomplishing His creative will in perfect accord with His goal to
    establish the Kingdom on Earth.

    > I have read before that you believe God is involved even in random events,
    > such as random mutations. I agree with that. But does that mean that (1)
    > God actually directs random events, i.e., chooses and brings about which ones
    > he/she wants to have effected, or (2) that God merely knows what the outcome
    > will be? If (1) then you have _directed_ evolution, and that's a far cry fro
    > m what the mainstream evolutionary biological community believes, if my
    > understanding of it is correct.

    God is continually active in Creation. If God were to withdraw His hand
    the universe would cease to exist. Thus, I do not believe that God ever
    intervenes in Creation because He never leaves it! How God works in and
    through the Creation to accomplish His creative will I do not know. A
    complete evolutionary explanation for the history of life changes God's
    continuing, personal, intentional creative action not a wit. Just as
    knowing how I developed from an unfertilized ovum changes my conviction
    that I am an individual creation of God not a wit.


    Buchholtz, E.A., 1998, Implications of vertebral morphology for locomoter
    evolution in early cetacea. IN, J.G.M. Thewissen (ed.), The Emergence of
    Whales, Plenum Press, New York, p. 325-351.

    Williams, E.M., 1998, Synopsis of the earliest cetaceans: Pakicetidae,
    Ambulocetidae, Remingtonocetidae, and Protocetidae. IN, J.G.M. Thewissen
    (ed.), The Emergence of Whales, Plenum Press, New York, p. 1-28.

    Thewissen, J.G.M., 1998, Cetacean origins: Evolutionary turmoil during the
    invasion of the oceans. IN, J.G.M. Thewissen (ed.), The Emergence of
    Whales, Plenum Press, New York, p. 451-464.

    Thewissen, J.G.M., Hussain, S.T., and Arif, M., 1994, Fossil evidence for
    the origin of aquatic locomotion in archaeocete whales: Science, vol. 263,

    Gingerich, P.D., Raza, S.M., Arif, M., Anwar, M., and Zhou, X., 1993,
    Partial skeletons of Indocetus ramani (Mammalia, Cetacea) from the lower
    middle Eocene Domanda Shale in the Sulaiman Range of Punjab (Pakistan):
    Contributions from the Museum of Paleontology, University of Michigan, vol.
    28, p. 393-416.

    Gingerich, P.D., Raza, S.M., Arif, M., Anwar, M., and Zhou, X., 1994, New
    whale from the Eocene of Pakistan and the origin of cetacean swimming:
    Nature, vol. 368, p. 844-847.


    Keith B. Miller
    Department of Geology
    Kansas State University
    Manhattan, KS 66506

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