My cursory understanding is that actuarial senescence (the increase in mortality rates for older populations) is not the primary driver of life span in most mam

My cursory understanding is that actuarial senescence (the increase in mortality rates for older populations) is not the primary driver of life span in most mammals.[1] Particularly small mammals, like lab rats. Whereas for first-world humans, it's the primary driver. Actuarial senescence makes it devilishly difficult to achieve significant life expectancy gains. Because mortality rates increase with age, life expectancy gains only scale O(sqrt(N)) with mortality reductions. Paradoxically a 40% reduction in all-cause mortality across all ages only adds 5 years of life expectancy.[2] The problem with life extension studies is small animals is that we may be measuring the wrong thing. A true breakthrough in human life spans will require slowing the rate of actuarial senescence. A wonder drug that only targets base rate mortality might double the mouse life span, but only add a few years to human life. [1] https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3000432 https://journals.plos.org/plosbiology/article?id=10.1371/jou... [2] https://joshmitteldorf.scienceblog.com/2012/11/10/mortality-and-life-expectancy/ https://joshmitteldorf.scienceblog.com/2012/11/10/mortality-...