The irony here, if I understand the thesis, is that the robust, pugnacious, resilient pioneer types whom Robert Heinlein idealized, are precisely the opposite of the actual subjects of a hypothetical Ira Howard Foundation project. Namely, that the heredity which is selected for in marginal and harsh environments - most of human existence prior to the late nineteenth century, in the formulation of the linked essay - is for fast-burners, short-lived members of the species who are capable of surviving deprivation, disease, stress and predation through their youth & long enough to reproduce. Supposedly the removal of such environmental stressors due to the onset of late modernity is allowing slow-burners to reproduce more effectively, thus increasing the average lifespan of the species.
Given that late modernity also presents an increasingly low birth rate to parallel the increase in average lifespan, I rather suspect that this theory is bollocks. I just was amused by the thought of Heinlein rolling over in his grave at the thought of a real world equivalent of his Lazarus Long being an uncoordinated, impractical, hollow-chested, introverted, under-sexed Last Man.