Has the Rate of Human Aging Already Been Modified?

In recent years, three hypotheses have been set forth positing variations on a common question-Has the rate of human aging already been modified? There is no disputing that people now live longer than ever before in history, and considerable variation in duration of life persists as a fundamental attribute of human longevity, but are these events caused by a measurable and verifiable difference in the rate at which people age, or are there other reasons why they occur? In this article, I explore the historical record involving changes in survival and life expectancy at older ages dating back to 1900, and examine what factors will likely contribute to changes in longevity in the United States through 2040. Evidence suggests that despite the absence of verifiable metrics of biological age, delayed aging is unlikely to be a cause of secular increases in life expectancy, but it could explain variation in survival among population subgroups, and it is the most likely explanation for why exceptionally long-lived people experience less disease and live longer than the rest of the population. If genetic heterogeneity explains any significant part of current variation in longevity, this opens the door to the development of therapeutic interventions that confer these advantages to the rest of the population.