That could be the partial exception that proves the rule (partial because there seems to be no "great(N+1) grandmother effect" as great grandmothers would start

That could be the partial exception that proves the rule (partial because there seems to be no "great(N+1) grandmother effect" as great grandmothers would start to compete with grandmothers, with low to none returns to human species). Are there other examples, besides high level primates? Moreover, that precise example hints that it shouldn't be so difficult to tweak the human substrate to improve the lifespan since Nature was able to do it in such a short time.