IIRC, and I'm old and forgetful so allow me some slack, there have been several studies on such founder effects. IIRC, one of the features supporting the multiple immigration events into the new world is the geographic distribution of blood types. As you move further south you find that the native populations consist of only one of the three possible blood types, while in north america, two of the blood types are found. This seems to indicate at least two migration events, one where the pilot population consisted of only one blood type, a later immigration that was either all of a second blood type or of a mixture of the two types.
There is alos the Cohen effect.
But neither of these points to speciation.
Aslan is not a Tame Lion
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