Professor:

Your statement was:

"if one survived infancy you stood a very good chance of attaining your three score and ten."

The article says (emphasis mine):

The early years from infancy through to about 15 was perilous, due to risks posed by disease, injuries, and accidents. But those who survived this hazardous period of life could well make it into old age.

COULD well. But didn't necessarily.

And also:

scientists have compared the life span of adults in contemporary hunter-gatherer tribes

We're not talking about "contemporary hunter-gatherer tribes", but of pre-industrial populations in the 18th and 19th centuries.

Guess again.