Why are such long lives recorded in Genesis?Adam, the first man, lived to be 930 years old (Genesis 5:5). Seth was 912. Five generations later, God took Enoch when he was 365 (Genesis 5:24). Enoch's son, Methuselah, died at 969 (Genesis 5:27). Methuselah's grandson Noah, ten generations after Adam, lived to be 950 (Genesis 9:29).
All of these men were born and, excepting Noah, lived their entire lives before the Flood. After the Flood, life spans dropped quickly. Noah's son Shem lived to be 600 (Genesis 11:10-11). The next three generations died in their 400s (Genesis 11:12-19). But six generations later, Abraham died at 175. So, Adam was 930; ten generations later, Noah was 950; ten generations later, Abraham was 175 (Genesis 25:7).
Why did people live so long in Genesis? And why the big difference after the Flood? We can only speculate. Adam was the genetically perfect creation of God. He had no physical or genetic faults. He would have passed on this incredible health to his children. Most of the patriarchs from Adam to Noah lived over 900 years. The exceptions were Mahalalel, who only made it to 895, Enoch, who was taken early by God, and Lamech who, at 777, had to die before the Flood. Each of these men inherited most of Adam's genetic perfection.
The sudden decline in lifespan after the Flood was probably environmental. Cultivated fields were wiped out. Animals were both more leery and more aggressive. Before the Flood, the land had been a perfect creation cursed. Now it was completely obliterated. In addition, something changed in the human body to benefit from eating meat instead of just plants—whether this was because natural human mutation after the Flood required a different set of nutrients or if God used meat to shorten lives, the Bible doesn't say.
The second major event that seemed to affect life spans is the Tower of Babel. We don't know exactly when the Tower of Babel was built except it was in the days of Peleg (Genesis 10:25). It's interesting to note that Peleg and all the generations after him saw their life spans cut in half, at least. In fact, Noah's son Shem and his next three descendants outlived the next five generations. Shem, Noah's son, outlived Terah, Abraham's father. Apparently, the dispersion of people groups from a central, civilized location did nearly as much damage as the Flood had done.
Our shortened lifespan today is a blessing. A good man could accomplish great things in 900 years, but Genesis 6 illustrates that long life doesn't equate to a good heart. An evil man with 900 years to scheme can do an incredible amount of damage—so much so that God saw fit to destroy the entire world. As God protected fallen man from living forever in Genesis 3:22, He protected us from living long enough to sin as badly as the generations in Genesis had.
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Truth about Humanity