On the Origins of New Forms of Life

9: On the Origin of Mammals

         
All that we see could be other than it seems. Indeed, anything we describe could be other than it seems. There is no a priori order of things.
—Ludwig Wittgenstein,
Tractatus Logico-Philosophicus

Section 9 is intended to illustrate how the alternative intellectual perspective provided by stabilization theory can enhance understanding of the evolutionary process. The case considered will be the origin of mammals. The typical biology text gives the following account of the origin of the various mammalian orders (usually referred to as the “mammalian radiation”):

  1. A "small, primitive, generalized" mammal living in the early Cretaceous was the common ancestor of marsupial mammals (in which the young are born at an early stage of development) and of placental mammals (in which the young are born at a later stage of development);
  2. By the end of the Cretaceous, some 60 million years later (approximately 70 million years ago), small, “primitive,” “generalized” marsupials and placentals existed;
  3. With the demise of the dinosaurs, placental mammals quickly “radiated” into the "adaptive niches" vacated by their former reptile overlords;
  4. Ever since, the various major categories of mammals (hoofed herbivores, insectivores, whales, bats, carnivores, edentates, monkeys, rodents, seals, etc.) have remained relatively stable.

Such is the usual account given of the genesis of mammals. But another story can be told, which is, in many ways, more consistent with available data. Section 9 reevaluates the origin of mammals from the standpoint of stabilization theory, and in so doing, reaches some radically different conclusions. Stabilization theory presumes the origin of new forms of life through stabilization processes is a typical, widespread phenomenon. There is therefore no reason to propose or to seek to identify a common ancestor of all mammals. Instead, the basic approach will be to seek similarity sets (see Section 8) of precursor forms that could give rise to each of the various major types of mammals.

         


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9: On the Origin of Mammals - © Macroevolution.net