The rapid decline in biblical lifespans
Mathematics tells us the numbers are not made up
Published: 5 October 2021 (GMT+10)
The dramatic decline in human lifespan after the Flood has been studied by many scholars. However, most studies only focus on the chronogenealogies of Genesis 5 and 11, which go from Adam to Terah, the father of Abraham. Yet, it is possible to add multiple additional generations by considering the details given to us in the rest of the Old Testament. The remaining data not only support the Genesis narrative, but they argue strongly that the lifespans in Genesis were not a creative invention of some early scribe.
The drop in lifespan is profound after the Flood. Noah and his sons lived for centuries, but by the time of David, people were living ‘normal’ lifespans (Psalm 90:10). What caused this is a matter of speculation, but we lean toward a genetic or genetic/environmental answer and we generally reject the older idea that a ‘vapor canopy’ once shielded the earth and protected and preserved people so that they could live for very long times. An additional issue is the phenomenon of patriarchal drive, whereby very old men fathering children in a small but growing population will cause bursts of mutations in select lineages.
Skeptics have often derided the great ages of the antediluvian and early post-Flood Patriarchs. We have contended with them more than once, defending a straightforward reading of Scripture as best we could. One important point, often overlooked, is that the data are not just found in Genesis 5 and 11. Instead, when you examine the rest of the Bible, we see that the declining trend spans the entire biblical period. Initially, the post-Flood people were living for several centuries. Ten or more generations later, Abraham, Isaac, and Jacob also lived for very long times, but not nearly as long as their ancestors. A few generations after this, the siblings Moses, Aaron, and Miriam died right at the upper edge of the modern human lifespan. By the time we get to king David, we are essentially in the ‘normal’ range of human lifespan. Yet, when combined, the ages fall into a beautiful mathematical continuum. Had someone invented those numbers, perhaps in a scenario where Genesis was written much later than conservative scholars assert, would they have thought to go through the rest of Scripture, teasing out the minutiae that are often buried in inconsequential locations and making sure they also fit the pattern? Consider that ancient people did not have the mathematical tools we have today. Nobody had ever made a graph, and they had only a vague sense of a timeline. They did not have the tools required to fit exponential decay curves to consecutive data points and, since their contemporaries would not have rejected the thought of long lifespans, little reason even to try.
For the sake of simplicity, in this discussion I am using the Masoretic Hebrew Bible and assuming a ‘short’ Sojourn of 215 years for the Israelites in Egypt. A further discussion of these topics is outside the scope of this article. Yet, using a long Sojourn of 430 years or an extended Septuagint timeline would not change the conclusions overmuch. Once the data (table 1, at end of article) are all in one place, we can present a visual representation. Figure 1 shows the ages of every person in the Bible for whom we have sufficient lifespan data and the number of generations that had passed since the Flood (with Noah = generation 1).
Fitting a power function to the biblical data (figure 1), we can see that each generation lives, on average, about 88% as long as the generation prior. Amazingly, the data are very consistent, with an “R-squared” value of 0.94. In other words, the line encompasses about 94% of the variation in the data set. A perfect fit would equal 1.0. I’ve run many experiments where I expected a similar relationship and yet got worse results than presented to us in the Bible! The thought that someone made up the numbers in Genesis 11 and then changed all the other data points in the Bible to make sure they fit a power function is preposterous.
There are some assumptions in the data, however. For example, in figure 2 we can see that Levi was both Moses’ grandfather (through his mother) and great-grandfather (through his father; yes, Moses’ father married his own aunt). I picked the paternal lineage to calculate the number of generations for Moses. Also, what are we supposed to do with Jacob’s father Isaac? His parents, Abraham and Sarah, were half-siblings (Genesis 20:12). In the end, he was genetically as far away from his grandfather as were his parents. Thus, Abraham and Sarah effectively gave birth to their own genetic brother! Then again, the reproductive cells went through an entire extra generation, so it really does not matter that Abraham, Sarah, and Isaac were all about 50% identical to Terah. The reproductive process would have added extra mutations (a small percentage) to Isaac’s genome, changed telomere length, and possibly affected other genetic factors that are associated with reproduction.
There is also something strange happening with Joshua and David (figure 2, bottom left). Joshua was born before the Israelites left Egypt. David was born some 450 to 500 years later, yet Joshua is 25 generations removed from Noah while David is only 24. Are there ‘missing generations’ in David’s lineage? This is unlikely. The original source for David’s genealogy during the period of the Judges is found at the end of the book of Ruth. Yet, it is repeated verbatim in 1 Chronicles 2, Matthew 1, and Luke 3. Matthew goes as far as to say that Salmon fathered Boaz by Rahab1 and that Boaz fathered Obed by Ruth. Thus, he is directly connecting David’s genealogy to other events in the Bible. There is little wiggle room here.
The solution to the Joshua vs David question comes from the fact that in any population you will have overlapping generations. At any given time, a long line of eldest sons (with the shortest possible average generation time) will be living alongside a short line of youngest sons (with the longest possible average generation time). Consider the only recorded question Pharaoh asked Jacob when he arrived in Egypt, “How old are you?” (Genesis 47:8, paraphrased with added emphasis). Jacob’s grandfather, Abraham, had visited Egypt some 200 years prior (Genesis 12). Pharaoh, due to the laws of primogeniture, was the oldest son of an oldest son going as far back as anyone could imagine, or at least to the start of his dynastic line. Abraham may have met a pharaoh from ten generations earlier. There are many records of important old men having children late in life in the Bible, including Abraham (Genesis 25:1–6) and Hezron (1 Chronicles 2:21). Consider that David is specifically listed as the youngest of the eight sons of Jesse (1 Samuel 10–13). It would only take a few generations like this to span a considerable period of time. Consider also that a grandson of President John Tyler (1790–1862) is still alive.2 Overlapping generations are a fact of life (see Patriarchal drive in the early post-Flood population, figure 8), so the fact that the number of generations that separate Joshua and David from Jacob are so similar is not entirely unexpected, given what we know about human genealogy.
Figure 3 shows the same data but graphed according to birth year. “AM” means anno mundi, or ‘year of the world’. Using a straightforward addition of the ages in the Masoretic text of Genesis 5, Noah would have been born about 1,056 AM. Notice that the data fit a power function about as well as in Figure 1, yet the curve does not seem to fit nearly as well in the first several generations. This is due to the long gaps of time between those first several generations compared to the rest. Graphing according to birth year is not the best representation.
Since several of the sons in the list lived longer than their father, there does not seem to be a significant relationship between the age of the father and the drop in lifespan in the next generation. One might also expect cumulative effects, but since there is such a wide difference in the ages at which these fathers had children,3 it is very difficult to see anything other than that the lifespans decline over time, which we already know. Even though one can estimate the number of cell divisions4 and the number of germline mutations5 from one generation to the next, this approximates the age of the father at paternity, so the calculations do not seem very promising.
In the end, the Bible provides a beautiful decay curve. This would be completely unexpected if the data are not real. Appeals to a misreading of biblical numbering schemes or to faulty translation from a sexagesimal counting system (i.e., base-60, like that found in multiple cuneiform writing systems) to a decimal system (base-10, like the system we use today) do not work. First, the opposite is more likely. Second, the rest of the biblical data fit too perfectly with the lifespans given to us in Genesis 5 and 11. Are the ages of the biblical Patriarchs outside the modern experience? Yes, they are. Should we doubt that the numbers are real? No, we should not. At least, biology does not preclude people living for centuries (see Living for 900 years), math tells us there is a real trend in the data, and logic tells us that nobody made up those numbers out of whole cloth.
Table 1: Genealogical data for various people in the Bible. “AM” = anno mundi, or year of the world. These dates are generated by simply summing the ages of the fathers when the child is born. This almost certainly induces uncertainties. For example, from one generation to the next, we are not given dates in reference to the age of the earth but to the age of the father. To convert to a calendar year, you would have to factor in that about half the time a son is born before a father’s birthday. Thus, over the 20 generations between Adam and Abraham, about 10 additional calendar years should be added. In the end, these dates are only approximate. See How long were the Israelites in Egypt?. BC dates prior to Abraham were calculated by simply subtracting the age of each father at paternity and have the same caveats as the AM dates. There are some contentions about the specific dates for some of the kings of Judah, but I took the conservative position in each case. I also included Anna, the prophetess who, at 84 years old, had lived long enough to see the Messiah (Luke 2:36–38), although she does not appear in either figure. We do not know when she actually died. Dates in red are reasonable approximations.
|Person||Birth (AM)||Birth (BC)||Generation||Lifespan|
References and notes
- Rahab is the Canaanite prostitute that famously rescued the Israelites spies when they went to reconnoiter Jericho prior to the Israelite invasion. See Joshua 2 and Joshua 6:22–25. Return to text.
- Brockell, G., The 10th president’s last surviving grandson: A bridge to the nation’s complicated past, The Washington Post, 29 Nov 2020; washingtonpost.com/history/2020/11/29/president-john-tyler-grandson-harrison. Return to text.
- Consider that there are seven generations in a row (from Salah to Terah) where the father is only about 30 years old. Is this a list of eldest sons? In other words, would Abraham, or perhaps his nephew Lot, have been in the line of succession to be the chieftain of his Patriarchal tribe? See Genesis 14:13. Also note that the word “Hebrew” is spelled the same as “Eberite”. See The forging of the Israelite nation. Return to text.
- See Crow, J.F., The origins, patterns and implications of human spontaneous mutation. Nature Reviews Genetics 1:40–47, 2000. His general formula for the number of cell divisions in the male lineage from one generation to the next is 35 + (age at paternity – age of puberty) x 23. Return to text.
- See also Kong, A. et al., Rate of de novo mutations, father’s age, and disease risk. Nature 488(7412):471–475, 2012. Their general formula for the number of germline mutations from one generation to the next = age at paternity x 1.98 + 4.79. Note that it might not be valid to extrapolate this beyond the study group, i.e., modern Icelandic males. Return to text.