It is an unprovable theory, since our records from the past mix truth and fiction so completely, but it is possible that modern humans differ significantly from pre-(H)istory humans. Oh we know our outward appearance is the same, and we definitely still have the same organs and all that, but some records we have of supposed "top tier" athletic individuals from pre-(H)istory times are shockingly unimpressive.
Our modern records easily show that, for instance, a weight lifter who focused on training each day can steadily increase their the amount they lift year over year. Although there is slowdown over time, it is also always possible for them to increase the weight that they can manage. Age eventually does diminish strength, but only past the age of 70 to eighty years old. Pre-(H)istory weightlifters often topped out at a bit under 500 lbs.
Perhaps we are simply fitter and have less toxins in our body to account for this difference.
Or perhaps this is yet another forgotten gift from a long departed God.
I know what I believe.
-Theories on modern biology, by the Head Priest