Whether large bird and mammal brains arise from common descent or convergent evolution is uncertain

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From paleontologist R. Glenn Northcutt’s “Evolving Large and Complex Brains”(Science, 20 May 2011) we learn:

During the Mesozoic (~250 million to 65 million years ago), two distantly related groups of reptiles—the cynodont (or mammal-like) reptiles and the coelurosaurian theropod dinosaurs—gave rise to mammals and birds, respectively. Both mammals and birds evolved brains some 10 times as large, relative to a given body weight, as those of their ancestors (1). In both groups, these brains contributed to the evolution of the ability to control body temperature (endothermy) and complex social interactions, including parental care and a reliance on learning that even involves tool use (2, 3). The size of most parts of the brain increased in birds and mammals, but the cerebral hemispheres and cerebellum, both of which are involved in sensory and motor integration, underwent particularly spectacular development (see the figure).

Although mammals and birds evolved from distantly related groups of reptiles, the higher integrative centers and circuitry of their cerebral hemispheres are very similar, and comparative neurobiologists continue to vigorously debate whether these centers evolved from the same ancestral neural centers (4, 5) or from different ones (6–8). Speculation about the evolutionary steps leading to large and complex mammalian and avian brains is equally contentious and unresolved, in part because of the rarity of fossil skulls and, until recently, the need to destroy such skulls in order to expose the endocasts (casts molded by the cranial cavity). Typically, endocasts are the only record of the brain’s outward appearance in a transitional form, because brains themselves are rarely fossilized.

File this with “Snakes and limbless lizards evolved independently – researchers” Some progress can surely be seen in the fact that convergence is even being considered. This is certainly an area of evolution where convergence on a common tendency is highly  plausible because  both birds and mammals are warmblooded, and an increase in intelligence requires only a suitable brain platform, not a specific one.

3 Replies to “Whether large bird and mammal brains arise from common descent or convergent evolution is uncertain

  1. 1
    Mung says:

    OT: The rapture actually happened, and I am living proof!


  2. 2
    Mung says:

    It’s a known fact that brains can only get smaller through time.

    For brains to get larger would violate the first law of Genetic Entropy, the second law of Thermodynamics, the third law of Dollo, and the fourth law of conservation of small-brainedness.

    The interesting question is not descent vs. convergence, but rather why do brains get larger (when they do) and why do brains not get larger (when they don’t), and why do brains stop getting larger, and how is it that a single over-arching theory manages to explain each of these by recourse to the exact same “mechanism.”

    According to information theory, if you already know the answer, you’ve not gained any information.

    Thus Darwin’s theory is shown to not increase our information.

    Is that because Darwin’s theory violates the second law of thermodynamics?

  3. 3
    Robert Byers says:

    is brain size relative to intelligence or greater need for function? who says?
    Brain size could be, probably is, just relative to minor matters of practical needs like optics or this or that.
    its a presumption that brain size matters in animals.
    It doesn’t matter in people. The smartest folks.
    Bigger people have bigger brains. men over women etc.
    Anyways the bible says we think in our heart and not our mind. Our soul is our intelligence. Not our machine in our head.
    Once again evolutionists are forced to invoke convergence to explain like results in unlike groups.
    Yet in fact once again the common blueprint of nature explains why unrelated creatures have like results.
    There are no mammals or reptiles or inbetweens .
    they are unrelated kinds with like results for like needs from a like program from a creator.
    its been a glorious errot in classification of life.
    So endlessly they must invoke convergence in so much of biology. More to come.
    if there was a creator and a common blueprint for common needs then it would be that like results are in unlike life.
    So convergence would be very common and need to be explained.
    Therefore it would become a problem for a theory that sees happanchance on mutations as the creator.
    It might be that the great convergance known and recently and in the future discovered in biology will really put to the sword evolutionary biology.
    This article is a example.

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