Need or demand will dictate the event. We may not understand the stressor responsible for specific chromosomal differences but cause will create the effect.
The decreased chance for procreation may in fact be another part of the selection process. The females remaining without progeny as they are unsuitable to carry the blueprint for the chromosomal change correctly.
It may be that the carrier of the chromosomal change is selecting for identical alleles.
Bit over my head, but thought provoking which I always appreciate.
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The question is, however - how is this point reached, and why has it happened so often during the course of evolution?
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How is the point of the trait being homozygous met? Perhaps through the above selection criteria?
Why has it happened so often during nature? I assume it is to do with neccessity. As plants develop better defenses (say tougher seeds) animals develop better beaks/claws/teeth which calls for better predators or they might get pecked to death... Everything affects everything, in some manner, a change promotes more change.
The reappearance of the sabre tooth several times in the fossil record denotes emerging populations of large herbivores around the time of the emergence of the tigers. Supply and demand. Nothing more. Species may differentiate according to the attributes deemed neccesary.
Why would the human form/make-up change now?
The desire to fly. Pollution filtration or even utilisation. Dietary adjustments. Plus plus plus.
Sorry if I'm not in the right ball park, point it out if so.
And the different humans - australian aboriginals?
