- #36
jim mcnamara
Mentor
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This is the definition of an isolated population, the basic "unit" of the process of speciation. Isolation can be one many things, some examples:Long term isolation of a group of individuals
physical - ex: season or time of day for flowering, incompatible pollen/stigma, change in estrus pheromones, coloration.
geographic - ex: on an island, surrounded by glaciers in a valley, in a dry zone surrounded by a swamp.
behavioral - male displays, mating calls,
genetic - polyploidy (different numbers of chromosomes), parthenogenesis
For all of these speciation is also a function of generation time - hours like a mayfly, 18 years like humans.
And the most important point: our definition of species is largely arbitrary. Lots of exceptions and edge cases. It is an idea with great convenience for us humans cubbyholes to classify things. Nature doesn't give a darn about convenience.
Normally we think of species as unable to interbreed and produce fertile offspring - like mules = horse interbred with ass
Example exception: modern European humans have a tiny part of the Neanderthal genome, Asian humans a tiny part of the Denisovan genome. So, if those earlier humans were truly separate species, then why did mating with modern humans create viable offspring? Were they truly separate species or not, is the crux of the matter. Part of the answer is that evolution of the genus Homo is "bushy", not linear at all.
Really good article:
https://www.learner.org/courses/biology/units/humev/experts/tattersall.html