Speciation and "punctuated Equilibria"
A major evolutionary problem has been how the continuous process of evolution produces groups of individuals, labeled species, whose adult members look extraordinarily similar, and distinctively different from the members of other species. Lions and leopards are, for instance, both large carnivores inhabiting the same general environment, and hunting much the same prey, in much the same way, but they look extraordinarily different, and would not be confused one for the other even by the most unsophisticated observer. There would seem to be no obvious evolutionary reason which suggests that lion-leopard intermediates are likely to be less successful hunters than either of the two distinct species that inhabit the African savanna today. Why then do they not exist? What evolutionary force drives these intermediate forms to extinction, leaving only highly uniform and distinctive lions on the one hand and highly uniform and distinctive leopards on the other?
This is, however, only one aspect of what is almost certainly a two-dimensional problem. The "horizontal" dimension refers to the almost complete absence of transitional, or intermediate forms between present-day species (e.g. between lions, leopards, cheetahs and lynxes). The "vertical" dimension concerns the fossil record. Fossil species are frequently remarkably stable over extremely long periods of geological time, despite continental drift, major climate changes, and mass extinctions. When a change in appearance or form does occur, it tends to be abrupt in geological terms, again producing phenotypic gaps (i.e. an absence of intermediate forms), but now between successive species, which then often co-exist for considerable periods of time. Thus the fossil record, though open to different interpretations, suggests that evolution occurs in bursts, interspersed by long periods of evolutionary stagnation (i.e. by means of punctuated equilibria). Why this is so, has been one of evolution's great mysteries.
Koinophilia could explain both the horizontal and vertical manifestations of speciation, and why it usually involves the entire external appearance of the creatures concerned. If sexual creatures prefer mates sporting predominantly common features, and avoid mates with unusual, unfamiliar, fringe, or extreme attributes, then common features will tend to become more common still, and at a rate and to an extent that natural selection on its own is unlikely to achieve. Since koinophilia affects the entire external appearance, the members of an interbreeding group will soon all begin to look astoundingly alike, both with regard to important or essential features (e.g. the jaws, dentition, and claws of a lion) and trivial features (e.g. the black furry tuft at the tip of the lion’s tail, or the lion's “beard”). It is almost inevitable that each interbreeding group will, in this way, very quickly develop its own characteristic appearance. An individual from one group who wanders into another group will consequently be recognized as being different, and will, therefore, be discriminated against during the mating season. This koinophilia-induced reproductive isolation might thus be the first crucial step in the development of, ultimately, physiological, anatomical and behavioral barriers to hybridization, and thus, ultimately, full specieshood. Koinophilia will thereafter defend that species' appearance and behavior against invasion by unusual or unfamiliar forms (which might arise by immigration or mutation), and thus be a paradigm of punctuated equilibria (or the "vertical" aspect of the speciation problem), and stabilizing selection.
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