Change "say" to "should say" and that was my entire point. I did not say all biologists are going crazy with suppositions.
Variances arise within a species. During fat times, all survive, so combinations of multiple mutations are possible...During lean times, natural selection gives some species an advantage. Barriers permit some populations to evolve separately from others, even when they may be initially the same populations.
I'm seeing no difference here from what I stated, other than that I hypothesized that some variations may be predisposed to occur in certain species. Those variations might or might not help survival.
It is hard to suppose how the Panda's restricted diet and less than efficient reproduction was ever a plus for survival, yet it is what it is, i.e. it survived. It might be rational to presume that bamboo was plentiful enough, and the reproduction plentiful enough, versus thinking about the Panda having any sort of advantage.
Imagine how tough it would be to be a predator who ate Pandas.
The Lodka Volterra equations relate predator-prey numbers (I used to be a programmer for Dr. Schaefer at Univ of Ariz).
First, there are never enough to support mutations that make predation on Pandas easier. Second, if such a mutation occurred, it would die out after Panda numbers got small.
What else eats bamboo? Little competition could be an advantage, bamboo grows quickly, and the sedentary nature and stored energy permits the Panda to survive periodic reductions in bamboo availability. It is doubtless a vulnerability. A bamboo killing fungus would probably kill the panda too.
By comparison, consider the hoofed rat (aka whitetail deer). It overbreeds, and then starves absent predation. Hunting rules change to adapt to wide variation in its numbers, in an attempt to reduce mass starvation incidents.