[DouglasKC]

Fascinating. What is the physical mechanism that defines the limits that cannot be crossed?

Self correcting DNA. From Molecular Biology of the Cell

[From many - one.]

Not an a answer since you accept heritable, intraspecific adaptation.

[Thatcherite]

Fascinating. What is the physical mechanism that defines the limits that cannot be crossed?

Self correcting DNA. From Molecular Biology of the Cell

Yes, the copying fidelity of DNA is extraordinary. However copying errors do occur, You and I both have several mutations from our parents, just like every other living thing on earth. At some loci in the human genome there are more than 100 alleles. Yet Adam and Eve had 2 each. Noah's sons and their wives had 2 each (and Noah's sons presumably shared half their genetic material with each other). All other species sequenced have similar genetic variation that cannot have arisen from a single pair c. 5000 years ago. The copying fidelity of DNA does not represent a limit to change, just a limit on the pace of change.