Wednesday, September 8, 2010

I’m Gonna Live Forever, Part 2

In an earlier post, I discussed people in their 20s and 30s today who dreamed of living to 200 years old. My arguments against the likelihood of this actually occurring were based on assumptions that life expectancy at birth is converging to 80 years old and that there is a maximum attainable age at approximately 120 years. I concluded admitting that there hasn’t been enough time to observe the aging process of those born after the great strides were made in health and sanitation. However, as I will discuss below, we can evaluate additional data on life expectancies that I believe support the convergence view.


In Figure 1 (above), we can see that most of the gains in men’s average lifespan are in the earlier years. For example, a man born in 1990 is expected to live nearly twice as long as the average man born in 1850. However, comparing two septuagenarians, the expected difference in years left dwindles down to less than four:

So, after a century and a half, all we have to show for a doubled life expectancy at birth is that the much of the advantage disappears after you’ve reached the age of 5. I don’t mean to trivialize the gains made combating infant and child mortality. However, the predictions are that old men fifty years from now aren’t expected to live any longer than old men born in the 1800s. Figure 2 (below) shows a similar pattern for women:


While a woman born in 1990 is expected to live twice as long as the average woman born in 1850, this advantage also shrinks later on in life. A thirty-nine-year difference at birth becomes a six-year difference at age 70:

Thanks to modern medicine, improved nutrition, and better sanitation, the average baby today doesn’t have to face the hostile environment that was responsible for killing millions of infants in history. He or she can expect to live decades longer than babies in the previous century. However, the elderly of the future aren’t predicted to live more than a few years longer than the average elderly person of the past. Adults who fancy themselves invincible should take note: The definition of “old” hasn’t changed. They put their trust in a scientific miracle being repeated when it never even occurred in the past.

*FIGURES 1 and 2: Data series constructed from “Table Ab656-703: Expectation of life at specified ages, by sex and race: 1850-1998,” Historical Statistics of the United States Millennial Edition Online (2006). Cohorts: Individuals grouped by birth year (14 groups). Horizontal axis: Specified age. Vertical axis: Life expectancy in years.