Cladogenesis

∞ generated and posted on 2015.12.28 ∞

Branching evolution.

With cladogenesis a single lineage gives rise, through speciation, to more than one lineage. In terms of lineages traced through time, there thus is a branch point where one lineage splits into two or more lineages (though, with splits not necessarily occurring exactly simultaneously if more than two new lineages form). Cladogenesis is the only means by which the number of species in the world can increase. See also clade and cladogram. Consider in addition the concept of adaptive radiation.

Whenever you compare two species in terms of their similarities – particularly homologies – you are implicitly looking at the products either of past cladogenesis events or potential future cladogenesis. That is, cladogenesis implies the existence of a common ancestor among two or more species, which is another way of saying that, through speciation, one species, sometime in the past, had given rise to more than one additional species (or, at least, one species gave rise to a new species and, meanwhile, this ancestor species has not yet gone extinct).

The easiest way to picture cladogenesis is to consider one population (i.e., one species) that has split into two separate gene pools, with both gene pools diverging evolutionarily from each other. The result in not just two distinct populations (i.e., two distinct species) but indeed two phenotypically as well as genotypically distinct populations. Thus, cladogenesis looks more or less like this (where sp = 1 species and spp = more than one species):

     1 sp → 2 distinct gene pools → speciation → 2 distinct spp

With slightly more detail:

     1 sp → 2 gene pools → speciation → 2 subspecies → 2 spp

In both cases, feel free to substitute "lineage" for "sp" and "lineages" for "spp".

"Clado" means branch, as derived from Greek, whereas "genesis" means "origin" or "beginning". Cladogenesis thus literally means "branched beginnings", though a perhaps better way of thinking of cladogenesis, the word, is as more than one beginning. That is, more than one branch or, more specifically, more than one lineage generated from a single species. One species, in other words, giving rise to more than one successful speciation event.

Of interest, anagenesis works more or less the same way, but where the multiple branches were extremely short – multiple attempts at speciation but in effect only one success – or either from the fossil record or among extant organisms we only know about one of the successes. In addition, with cladogenesis, the parent species has gone extinct, though this latter point is more or less a given since, in reality, all species after a relatively brief stay on planet Earth in fact go extinct (though the same, lucky for life on Earth, cannot also be said for all lineages).