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However, you've changed the terms of my argument somewhat, from Vertical Evolution (A into B) to Horizontal Evolution (A coexisting with B). That's not actually what I was talking about, but I can dig it.

Ah, well that is the standard model for speciation.

Let us say that you continually sub-divide the Species into less-survivable sub-groups of the Core Species.

What you end up with is a bunch of Genetic Variants which are relatively more vulnerable to Local Extinction Events (since their overall range of Adaptation is absolutely reduced) and a Genetic Core Species which is as vulnerable as ever to a Mass Extinction Event...

That's an interesting way of looking at it! But the problem is, we're talking about your hypothetical scenario: One species originally suited to "biomes" A, B, C, & D, splits into the original plus the second suited for C, D, & E. Why not postulate the offshoot being suited for B, C, D, & E? Or indeed why not A, B, C, D, & E? I've never heard of any evidence or biological/ecological principle that says that a breakaway subspecies or species has to be adapted to fewer environments than the original population was. It could just as easily be more.

Why not postulate the offshoot being suited for B, C, D, & E? Or indeed why not A, B, C, D, & E? I've never heard of any evidence or biological/ecological principle that says that a breakaway subspecies or species has to be adapted to fewer environments than the original population was. It could just as easily be more.

Well, that's sorta what I am asking. If you have evidence of either a horizontally-evolved sub-species, or a vertically-evolved successor-species, enjoying inherent genetic adaptability to more "environments than the original population was" (that is, an ABSOLUTE increase in genetic survivability), that's what I would be interested in seeing.

Because otherwise, given Local and Mass Extinction Events, Relative increases in Genetic Survivability won't cut it... we ultimately end up reading an Agatha Christie novel. "And Then There Were None."

I've never heard of any evidence or biological/ecological principle that says that a breakaway subspecies or species has to be adapted to fewer environments than the original population was. It could just as easily be more.

Actually the principle is quite simple. The biological diversity of 1,000,000 individuals will always be larger than that of 100,000 of its members. When you split a group you therefore get less biological diversity any way you cut it. If in addition the cut off group has been selected for a specific trait then the traits being selected against will be lost. Such traits might have been useful at a future time when circumstances change again (as they always do).