Obviously cloning from a perfect genetic specimen you don’t have inbreeding issues, and even with marriage between identical perfect specimens you aren’t going to have problems with genetic defects.
Its interesting that even without access to the “tree of life” these perfect specimens were able to live nearly ten centuries. As did their offspring, even once they started marrying spouses from the surrounding tribes (with the subsequent dilution of the genetic code) their offspring still had very long life spans.
We note that the long life spans ended with the flood which causes some people to assume that something about the mantle protected us from radiation damage to the genetic code. Still, even centuries later, we find patriarch living a century and a half which, compared to their forbears is nothing but compared to us its still quite remarkable.
It gives an inkling of what the body was designed to be able to do.
Who were the forebears of those "surrounding tribes?