page_title: Koinophilia
section_title: Speciation and punctuated equilibria
hierarchical_section_title: Koinophilia / Speciation and punctuated equilibria
caption_attribution_description: English: Part of a herd of Springbok in the Kgalagadi Transfrontier Park, South Africa.
context_page_description: Koinophilia is an evolutionary hypothesis proposing that during sexual selection, animals preferentially seek mates with a minimum of unusual or mutant features, including functionality, appearance and behavior. Koinophilia intends to explain the clustering of sexual organisms into species and other issues described by Darwin's Dilemma. The term derives from the Greek, koinos, "common", "that which is shared", and philia, "fondness".
  Natural selection causes beneficial inherited features to become more common at the expense of their disadvantageous counterparts. The koinophilia hypothesis proposes that a sexually-reproducing animal would therefore be expected to avoid individuals with rare or unusual features, and to prefer to mate with individuals displaying a predominance of common or average features. Mutants with strange, odd or peculiar features would be avoided because most mutations that manifest themselves as changes in appearance, functionality or behavior are disadvantageous. Because it is impossible to judge whether a new mutation is beneficial or not, koinophilic animals avoid them all, at the cost of avoiding the very occasional potentially beneficial mutation.
context_section_description: Biologists from Darwin onwards  have puzzled over how evolution produces species whose adult members look extraordinarily alike, and distinctively different from the members of other species. Lions and leopards are, for instance, both large carnivores that inhabit the same general environment, and hunt much the same prey, but look quite different. The question is why intermediates do not exist.
  This is the "horizontal" dimension of a two-dimensional problem,  referring to the almost complete absence of transitional or intermediate forms between present-day species (e.g. between lions, leopards, and cheetahs).
  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 form occurs, 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 long periods of time. Thus the fossil record suggests that evolution occurs in bursts, interspersed by long periods of evolutionary stagnation in so-called punctuated equilibria. Why this is so has been an evolutionary enigma ever since Darwin first recognized the problem.
  Koinophilia could explain both the horizontal and vertical manifestations of speciation, and why it, as a general rule, involves the entire external appearance of the animals concerned. Since koinophilia affects the entire external appearance, the members of an interbreeding group are driven to look alike in every detail. Each interbreeding group will rapidly develop its own characteristic appearance. An individual from one group which wanders into another group will consequently be recognized as different, and will be discriminated against during the mating season. Reproductive isolation induced by koinophilia 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).
caption: The overwhelming impression of strict uniformity, involving all the external features of the adult members of a species, is illustrated by this herd of Springbok, Antidorcas marsupialis, in the Kalahari Desert. This homogeneity in appearance is typical, and virtually diagnostic, of almost all species,[25] and a great evolutionary mystery.[7][24] Darwin emphasized individual variation, which is unquestionably present in any herd such as this, but is extraordinarily difficult to discern, even after long-term familiarity with the herd. Each individual needs to be uniquely and prominently tagged to follow its life history and interactions with the other (tagged) members of the population.[26][27]
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