Thursday, October 6, 2016

Methuselah and New Research on Human Lifespan

Source: NYPL
The Bible records a remarkable list of patriarchs with lives that spanned centuries. Among the men listed in the genealogy of Genesis 5, we find the oldest person mentioned in the Bible:
When Methuselah had lived 187 years, he fathered Lamech. Methuselah lived after he fathered Lamech 782 years and had other sons and daughters. Thus all the days of Methuselah were 969 years, and he died. (Gen. 5:25-27).
Methuselah is mentioned only twice outside of Genesis, both of which merely recap the Genesis genealogy.  It's also important to note that the numbers given in Genesis for Methuselah's ages differ in different manuscript sources.  The Masoretic text, which is the basis of most modern English Bibles, is translated above (in the ESV).  A version of the Septuagint, an ancient Greek translation of the Old Testament, gives his age as 167 at the birth of Lamech but still has him living to be 969.  Another ancient source, the Samaritan Pentateuch, lists his age as 67 when he fathered Lamech and only 720 years at his death.

Young-age creationists have taken these references to be accurate historical records of extreme longevity in the ancient patriarchs.  After the Flood, the lifespans of the patriarchs listed in Gen. 11 drop off precipitously, which implies that something happened to change our lifespans to the pitiful century or so that we survive today.

There are many different issues related to these genealogies and the Ancient Near East, but today I just want to focus on one: the feasibility of living 900+ years.  Think for a moment about the "wonders" of getting older.  Teeth fall out.  Hair falls out.  Organs stop working.  Joints wear out.  Do you really want that to go on for 900 years?  Is that even possible?

Some creationists claim that something in the environment changed our lifespan, perhaps radiation or something in our diet (like widespread meat consumption).  Other creationists argue that it's more likely to be a genetic change.  In other words, we're programmed to die when we do.  A genetic change could help explain why we undergo senescence, all those unpleasant changes to our bodies as we age.

New research published this week in Nature relates directly to this question.  A study of mortality data by Dong and colleagues suggests that human lifespans may have a natural limit of about 115 years.  We've known for a long time that human life expectancy has been going up steadily since we've been keeping careful track of such things.  In 1900, the average life expectancy for men and women was below 50, but today men and women can expect to live into their 70s.  That's a dramatic change over the course of just 117 years, and much of it can be attributed to advances in medicine.  We know more about how to live healthy lifestyles, and modern medicine really can cure what ails us.

By looking at the fraction of people surviving to old age (defined >70 years old), the researchers found that the greatest changes occurred for people more than 80 years old.  In other words, there was a steep increase in the number of people surviving beyond 80 years old over the last century, but that sharp increase was not seen in people living beyond 100.  Longevity hasn't changed much at all for people who live to see their 110th birthday.  Dong et al. interpret their findings as a natural limit to human lifespan of about 115 years.  They estimate that people who make it to 110 have about one chance in 10,000 of living to see their 125th birthday.

A superficial reading of this new research might suggest that it invalidates a straightforward reading of Genesis 5 and 11.  If humans can't live longer than 115 years, they surely can't live to be 969.  That would also make sense in light of our experience of aging and senescence.  Human bodies wear out as they age.

But let's think a little more carefully about this work.  Remember that one creationist suggestion is that a genetic change (or many genetic changes) brought about an alteration in longevity.  Aging involves constant and unavoidable senescence, and if someone was to live to 969, that entire sequence of senescence would have to change.  Otherwise, they'd be miserable.  They certainly wouldn't be having children at 187 years old like Methuselah!  Indeed, the entire idea of extreme longevity requires a change in senescence and aging.

Now we have more evidence from Dong et al. that there is a real limit to modern human lifespan.  It's not merely a matter of improving our environment.  With all the environmental improvements we've experienced over the past century, the extremely old individuals still don't make it much past 110 years old.  That would support the notion that human lifespan is determined internally rather than externally, which is the most likely explanation of how the patriarchal longevity could have changed so drastically.  So even though this research sounds like a slam dunk refutation of Genesis, it isn't nearly that simple.

There is much more to be said about longevity and life history, and there is a lot more to be said about the ages of the patriarchs as recorded in Genesis.  If you'd like more blog posts about this subject, shoot me an email.  I'd be happy to write more.

Dong et al. 2016. Evidence for a limit to human lifespanNature doi:10.1038/nature19793.

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