In Genesis 17:15–16, God tells Abraham that he is not to call his wife Sarai (my princess) any longer but Sarah (a princess), as she will have a son by Abraham and will become the ancestral mother of nations and kings. Then Abraham laughs and asks himself whether he (who would be 100 by the time a child was born to him) can even have a child and how could a then 90-year-old Sarah bear a child.
Some have alleged that there is a contradiction here because even Abraham’s own father, Terah, was 130 when Abram/Abraham was born.1 And another ancestor recorded in Genesis 11 (Shem) had his first son at 100 years of age. But Abraham is not basing his inward skepticism on his ancestry; rather, he is honestly reckoning with his own vitality and the infertility of his wife. It is perhaps the nature of those looking for a contradiction here that they conveniently forget the timeline of events and Sarah’s (up to this point) barrenness.
Genesis 16:16 says Abram was 86 years old when Hagar bore Ishmael to him. Then Genesis 17:1–2 tells us that 13 years have passed: because Abraham was now 99 years old. God then reiterates his covenant with Abraham (previously given in Genesis 12:2–3, 13:14–17, 15:5–6, and 15:18–21): “I am God Almighty; walk before Me and be blameless. And I will make My covenant between Me and you, and will multiply you exceedingly” (Genesis 17:1-2 NKJV ). It is at this time that God changes the name of Abram (great father) to Abraham (father of multitudes).
We know that Abram and Sarai (as they were then called, but hereafter called Abraham and Sarah in this article) had been married for several years and had no children. Knowing that Abraham was 10 years older than Sarah (based on Genesis 17:17) and assuming that Sarah had married at the average age of the time (about 16), then by the time Ishmael was born, Abram and Sarai had possibly been married 60 years and still had no children. Sarah was definitely barren . . . and there’s no doubt from reading Scripture that it wasn’t for lack of love between them nor for lack of trying as Abraham was a righteous man and believed God’s promise (Genesis 15:6). Furthermore, Sarah was considered beautiful (perhaps even youthful) as she aged (for example Genesis 12:10–20): in Genesis 20 we read that King Abimelech attempted to take 90-year-old Sarah as his wife.
But since the birth of his first child, Ishmael, with Sarah’s maid Hagar, another 13 years went by, and there were still no children with Sarah. So any hope that Abraham would ever have children with Sarah (humanly speaking) seems to be foolishness. And Abraham realizes he’s another 13 years older and may even begin to doubt that he could have any more children even with another concubine . . . which of course he would not even want to consider, realizing how much pain one time inflicted upon Sarah.
This was no small or bare promise by God: this was something so magnanimous that Abraham could not even fully grasp it.
Then God had told Abraham, not just that he would have one child, but God had told him he would make Abraham exceedingly fruitful, and “will make you into nations, and kings shall come from you” (Genesis 17:6). This was no small or bare promise by God: this was something so magnanimous that Abraham could not even fully grasp it. So in light of all that, Abraham says, “Shall a child be born to a man who is one hundred years old? And shall Sarah, who is ninety years old, bear a child?” By this time Abraham and Sarah have now potentially been married over 70 years and still had produced no children.
Abraham may have been thinking of his forefathers: after Shem, who had his first son at 100, nobody in his family line is recorded as having their firstborn son after the age of 70 (see Genesis 11:12–26). Even assuming that the men had five-to-ten-year–younger wives, it is obvious that both men and women post-flood were getting past peak fertility times by the time they were 70 for men and 60 for women (assuming that the child was born to the first wife), with the “best case scenario” being 100 for men. We are not told what the upper age limit of childbearing was for women, but Sarah’s being 90 at the birth of Isaac had to be an outlier (if not unheard of) by this time. If the husband and wife hadn’t had their first child by then, based on the genealogies of Genesis 11, it seems the odds were that they wouldn’t have any. If the couple had children before that age, it seems that the men could have children until maybe 130–140 years of age at the outer edge (as his father Terah did with both him and Sarah, e.g., Genesis 20:12). But it may have been a younger wife for Abraham’s birth after Terah’s first wife had died, and that almost certainly was the case with Sarah since she was Terah’s daughter by a different mother than Abraham’s. Plus, one very important point to make here: since both Abraham and Sarah were to be in the line of the Messiah, God quite likely providentially kept Terah fertile in his older years long past the normal years of fertility.2
By contrast, Abram’s first child was at 86. By the time of Genesis 17, he was 99 and had to be wondering if he would be more fertile than Shem. That seems impossible seeing how all Shem’s subsequent children had seen a drop in lifespan and fertility lifespan.3 And Sarah, at 90, had yet to prove that she could ever have children. And even if by some miracle she could get pregnant, could her body handle childbirth at this age, and would she live through it? As far as Abraham was concerned, she was barren and seemingly would always be barren as she perhaps (and most likely) had hit menopause (as she indicated later in Genesis 18). As an example, consider that the average age of menopause in US women is 51 years4 and the average lifespan is 81 years.5 Taking that “maximum fertility percentage” of 62.9% of life and extrapolating it to Sarah’s 127 years, we get a “maximum age for fertility” of 80 years old. If it was the case that Sarah had gone through menopause already, then Abraham knew that humanly speaking, it was game over! He might as well ask God to just make Ishmael the child of promise and move forward (which he did in Genesis 17:18).
It has everything to do with Sarah’s barrenness and Abraham’s age at the birth of his firstborn, and perhaps Abraham was beginning to notice his vigor wasn’t as strong as it was 13 years prior.
When viewed this way, from the likely perspective of the actual people involved, this has nothing to do with supposed “evidence for shorter lifespans.” It has everything to do with Sarah’s barrenness and Abraham’s age at the birth of his firstborn, and perhaps Abraham was beginning to notice his vigor wasn’t as strong as it was 13 years prior. Other concerns were for Sarah being able to actually take a baby to term even if she did get pregnant. And again, humanly speaking, Sarah almost certainly had already hit menopause, and Abraham knew that it was “impossible” for Sarah to have children. But even if she hadn’t yet (in Genesis 17), within the next few months she definitely had, as Genesis 18:11 makes clear.
If Abraham did stop to think about his ancestors, he realized that everyone after Shem had their firstborn by the time they were 70 years old. Plus he was aware that most of his ancestors had lived longer lives and that lifespans, and consequently fertility lifespans, were dropping.
But what is impossible humanly speaking is very possible with God (Genesis 18:14; Matthew 19:26; Luke 18:27). God had promised Abraham over and over that he would be the father of many nations. In Genesis 17:15–16, God had specifically promised that Sarah would bear Abraham a son. But both Abraham and Sarah struggled to see how God would accomplish this with their failing mortal bodies.
We know that Abraham trusted God, and lest we be too harsh on Sarah, she knew full well that she was physically beyond the age and ability to bear children naturally (Genesis 18:11–12). And although she did laugh, but then denied she had done so (Genesis 18:15), it may be that it was more out of despair with her own body and fear of having her innermost thoughts known than because of a skeptical mistrust. She knew she was past childbearing years, and her statement in Genesis 18:12 may also hint that Abraham was “past his prime” as well.6 One year later however, God’s supernatural restoration of Sarah’s womb and Abraham’s vitality resulted in the promised son, Isaac. Abraham and Sarah’s moment of too much inward focus and not enough focus on God’s ability to do the impossible was a brief interlude to an otherwise trusting and believing relationship, as the author of Hebrews attests.
By faith Sarah herself received power to conceive, even when she was past the age, since she considered him faithful who had promised. Therefore from one man, and him as good as dead, were born descendants as many as the stars of heaven and as many as the innumerable grains of sand by the seashore. (Hebrews 11:11–12)
There is no contradiction between Genesis 11 and Genesis 17:17 through chapter 18. Lifespans and fertility were decreasing. Since Babel, mutation and genetic drift had begun to affect people in the smaller populations that had migrated away based on newly acquired languages. Loss of technology, agricultural, medical, and herbal knowledge, etc., for some groups meant a dramatic decrease in age. Abraham, at 175, died in a good old age but did not live to be as old as his forefathers and ironically did not live to be as old as his son Isaac (Genesis 35:28). But Abraham’s father, Terah, and son, Isaac, were the two outliers in an otherwise steady decline from Eber to Joseph with few exceptions for the rest of Old Testament history.
There is no contradiction between Genesis 11 and Genesis 17:17 through chapter 18. Lifespans and fertility were decreasing.
When the data from Genesis 11 is examined, it shows that the human lifespans of those born after the flood follow an exponential decay curve. Abraham, like Jacob after him (Genesis 47:9) recognized that his lifespan did not match his forefathers, but God’s supernatural revitalization of Sarah’s womb and his own vitality meant that his slightly myopic outlook would be swept aside, not just with the birth of Isaac but with several sons with his next wife Keturah, after Sarah died (Genesis 25:2). God’s promise to Abraham of nations coming from his loins was vindicated, and most importantly, it was through Isaac and Jacob that the Messianic line would be established and through which Christ would come.