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Evolution
Evolution in Action
Divergent Evolution
Divergent Evolution
Peccaries (the Tayasuidae) diverged from the true pigs (the Suidae) about 40 million years ago. Since then the peccary line has split twice more, giving the collared peccary (Tayassu tajacu) of Argentina and the American southwest and two close relatives, the chacoan peccary and the white-lipped peccary of isolated, more tropical areas.

Such divisions are termed divergent evolution.

A macrotrend in phylogenetic diagrams over the last 225 million years has been one of increasing diversity and number of species. An ancestral pre-pig/peccary becomes two species, pigs and peccaries. The peccaries then diverge to become three types of peccaries. Nowhere in any phylogenetic diagram does a peccary reverse its evolution and devolve back into a pre-pig or pre-peccary.

Evolution is an irreversible phenomenon.

There is no going back. Genetic change followed by natural selection cannot reverse itself or exactly repeat itself. Precisely the same species can never form again after it has vanished and become extinct.

Each species, once it has been shaped and formed, is adapted to the immediate environment and uses what variation it has in its gene pool as the raw material for all subsequent changes. This imposes major limitations on what is possible and what is not possible for the next species that evolves from it.

Organisms follow evolutionary paths that are primarily exploitive. Feathers may have originally been adaptations to prevent heat loss on a small type of dinosaur, but when "flapped" they become airfoils that make flight possible.

Again and again an adaptation used in one context becomes the raw material for a completely new exploitation and evolutionary direction.

Figure legend: Divergent Evolution. A macrotrend in phylogenetic diagrams is for increasing diversity.

As shown for the horse, a fan-shaped diagram evolves as more and more species arise with the passage of time.

Beginning 54 million years ago with Hyracotherium, many different species of Old World and New World animals eventually gave rise to the modern horse species, Equus.


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© 2001, Professor John Blamire