sentences:  He points to studies of the demographic data in large-scale fruit fly experiments and actuarial data for humans which he believes support the hypothesis that acceleration in death rates can halt in later life.According to Rose, mortality-rate plateaus have not often been noticed in humans because they are only seen in specific-age cohorts of the very old.His proposed explanation is that at a stage of life beyond the potential to reproduce, the effect of natural selection is no longer falling as it has 'bottomed out'.