"How many generations have occurred since the Flood?
That depends on the usual age a woman was when she gave birth,
comprehensively averaged over the past 4,500 years. As an example, during that time were human mothers giving birth—on average (since many mothers have more than one child)—when they were 25 years old, or was it later when they were 33⅓?
In the first scenario, the new generation starts when the mother is 25, and in the second it starts when the mother is 33⅓.
A generation of 25 years equates to four generations per century, while 33⅓ years averages to three. If the standard generation is 25 years, there would be approximately 180 post-Flood generations. Likewise, if it’s 33⅓ years, only about 135 generations would result.
Consider a population replacement rate of 1.2, for example, as the average ratio of filial to parental population over 4,500 years. If one generation is 25 years, six reproducing adults would have one quadrillion descendants in the 180th generation because 6 × 1.2180 = 1,073,434,474,371,002.
Consider a population replacement rate of 1.2, for example, as the average ratio of filial to parental population over 4,500 years. If one generation is 25 years, six reproducing adults would have one quadrillion descendants in the 180th generation because 6 × 1.2180 = 1,073,434,474,371,002.
However, if one generation is 33⅓ years, six reproducing adults would have almost 300 billion descendants in the 135th generation because 6 × 1.2135 = 293,507,678,118. Obviously, Earth’s current population is not due to a ratio of 1.2 or higher.
Next, consider a smaller replacement rate—such as for every individual in a parental generation, there’s an average of 1.15 in the next generation. If one generation is 25 years, six reproducing adults would have half a quadrillion descendants in the 180th generation because 6 × 1.15180 = 505,548,136,684. (Still too many!)
Next, consider a smaller replacement rate—such as for every individual in a parental generation, there’s an average of 1.15 in the next generation. If one generation is 25 years, six reproducing adults would have half a quadrillion descendants in the 180th generation because 6 × 1.15180 = 505,548,136,684. (Still too many!)
However, if one generation is 33⅓ years, six reproducing adults would reproduce less than a billion descendants in the 135th generation, because 6 × 1.15135 = 938,338,851. (That’s not enough!) This means our planet’s current population resulted from a rate somewhere between these two averages.
Therefore, if the number of people on Earth came from generations averaging somewhere between 25 and 33⅓ years (for childbearing), a population replacement rate near 1.15 is about right. Such a modest rate yields no excuse for scoffers to reject Genesis by claiming that 4,500 years “isn’t enough time” for Earth to repopulate from only eight people to about eight billion today.
Therefore, if the number of people on Earth came from generations averaging somewhere between 25 and 33⅓ years (for childbearing), a population replacement rate near 1.15 is about right. Such a modest rate yields no excuse for scoffers to reject Genesis by claiming that 4,500 years “isn’t enough time” for Earth to repopulate from only eight people to about eight billion today.
As always, the Bible gets it right, and that’s what counts."
ICR