4. Population Growth – How Many Died in Noah’s Flood?

Noah, the Movie graphically portrays the devastation of Noah’s Flood, but it ignores a very intriguing question: How many people died in Noah’s Flood?

Forty-five hundred years ago Noah’s Flood wiped out the entire human population except for eight people: Noah and his wife and Noah’s three sons and their wives. Today’s
7 billion people are Noah’s descendants through 6 people — his sons Japheth, Shem, and Ham and their three wives (Genesis 9:18-19).
(See Tower of Babel – Origin of People Groups for information on the dispersal of Noah’s descendants across the globe.)

How Many People Died in Noah’s Flood?
Answer: Everybody outside the Ark

Population Growth Before the Flood

How many people died in Noah’s Flood?
The shortest and most accurate answer is “all but eight.” But how many does “all” include?

Prior to Noah’s Flood, population growth was much, much more rapid than today’s growth, because people lived much longer and had many more children. One can make calculations similar to those of previous posts to estimate the number of people who died in the Flood. However, this will be more speculative than the previous calculations, because we must estimate population growth parameters based on sparse data in Genesis.

From Adam to Noah’s Flood was 1656 years. If we assume for this period an average population doubling time of 74 years corresponding to 1804 to 2012 when humanity grew from 1 billion to 7 billion, then the world’s population would have been 10.9 million people at the Flood.

But this is surely far too low an estimate due to the much longer life spans, greater vitality and fertility, and far more children before the Flood. Let’s see if we can make a better estimate based on Biblical data.

I will need to estimate lifespans, the average number of children per family, and generation lengths for the pre-Flood years.

1. Lifespans

The lifespans of nine pre-Flood patriarchs Adam through Noah listed in Genesis 5 ranged from 777 years for Lamech to 969 years for Methuselah with an average of 912 years. This excludes the outlier Enoch, Noah’s great-grandfather whom God took to heaven prematurely at age 365 (Genesis 5:23-24).

Thus I will use 900 for the average pre-Flood lifespan.

2. Children

Each of the 10 patriarchs in Genesis 5 except for Noah is described as having “other sons and daughters” in addition to the named son. So each of them had at least 5 children and likely many more.

The age at which the patriarch’s named son was born ranged from 65 for Mahalalel to 500 for Noah. This named son was not necessarily the oldest or the youngest; for example, Adam’s named son Seth in the Genesis 5 genealogy had at least 2 older brothers (Cain and Abel). The average age of the Genesis 5 patriarchs at which the named son was born was 155. So clearly the pre-Flood patriarchs were continuing to have children at much greater ages than people sire children today.

The Jewish historian Josephus of the first century A.D. reports that Adam and Eve had 56 children — 33 sons and 23 daughters.
(Flavius Josephus, Antiquities of the Jews, Book 1, Chapter 2, Paragraph 2, Endnote 8.)

Josephus also reports that Lamech had 77 children by two wives. Lamech was the sixth generation after Adam through Cain; this was a different Lamech from the father of Noah through Cain’s brother Seth (Genesis 4:17-19).
(Flavius Josephus, Antiquities of the Jews, Book 1, Chapter 2, Paragraph 2.)

Scripture records data on the children of 10 families immediately after the Flood which can be useful for estimating pre-Flood practices. Noah’s three sons had at least 16 sons among them. Seven of those 16 grandsons of Noah had at least 38 sons among them. The progeny of the other 9 grandsons is not recorded. Thus 10 families immediately following the Flood had at least 54 sons and presumably about the same number of daughters, thereby averaging at least 10.8 children per family. (Genesis 10; 11:10-13)

Based on all this data, I will assume for estimation purposes that the average pre-Flood family had 10 children. This is probably a low estimate because men lived for so long and could have children at least through 500 years of age. If a family started at age 20 and had a child every 2 or 3 years to age 500, they could easily have over 200 children.

3. Generations

How long was a pre-Flood generation? Today a generation is about 35 years, because on average families complete child-bearing by about age 35. Only 400 years after the Flood, Sarah was considered too old to bear a child at age 90 (Genesis 17:17; 18:11).

I will use 90 years to be the average length of a generation before the Flood. Then the number of generations before the Flood averaged 18.4 (1656/90 = 18.4), and the number of generations in a lifespan averaged 10 (900/90 = 10).

Genesis 5 lists 10 generations for the line from Adam to Noah covering the 1656 years before the Flood. However, many lines probably had many more generations. A family line for which offspring were born starting around 20 could have produced over 80 generations in this period. So 18 is again a conservative estimate for the average number of generations in family lines before the Flood. It was probably much higher.

Similarly, the number of generations in a lifespan probably averaged much more than 10. But I will use these very conservative estimates in order to compute a conservative estimate of the population at the Flood.

4. Population at the Flood

I’m now ready to calculate an estimate of how much the population grew from Adam and Eve to the Flood in 1656 years. I assume an average lifespan of 900 years, an average of 10 children per family averaging 5 boys and 5 girls that grow to adulthood and marry, 18 generations on average in family lines, and 10 generations in an average life span. Most of these estimates are probably pretty good except for the average number of children in a family which I think was probably much higher. But these estimates will enable me to calculate a conservative lower bound for the Flood population.

Using the third population formula included below (in bold), these parameters (P=2, c=5, g=18, k=10) yield a population of 9,536,742,187,500. To this must be added the unmarried childless people who were alive at the time. A very conservative estimate for this is 8% of the reproducing population. This gives a total estimated population at the Flood of 10,299,681,562,500. This is over 10 trillion people! It corresponds to a growth rate of 1.783%. And I believe this estimate is low, since I used conservative estimates for the parameters.

This estimated pre-Flood population of 10 trillion is another indication that the Flood was worldwide. The Flood would have to be global to destroy such a huge number of people.

This estimated pre-Flood population of 10 trillion people is well over 1,000 times today’s world population of 7.1 billion people. How could this be possible? Is 10 Trillion a Reasonable Estimate for the Population at the Flood? This is the topic of the next blog post.

Population Growth Formulas

For those interested in checking the math, here are the relevant Population Growth formulas:
The population doubling time (length of time it takes a population to double) in years is
= T/d where T is the population’s elapsed time in years and d is the # of doublings.
= (log 2) / log(1+r) where r is the annual growth rate.

Starting with population P, the new population is
= P x 2^d after d doublings.
= P x (1+r)ⁿ after n years at an annual growth rate r.
= P x (c^g+1 – c^g-k+1) / (c-1) after g generations, where 2c is the average number of children per family who marry and have children (c boys, c girls), and k is the number of generations in a lifespan.

This last formula is derived as follows. Starting with an initial population P (consisting of P/2 men and P/2 women), the first subsequent generation would have 2c children in each of P/2 families for a total world population of
P + (P/2) x 2c = P(1+c).
The next generation would have 2c children in each of Pc/2 families for a total world population of
P(1+c) + (Pc/2) x 2c = P(1 + c + c²).
Similarly, after g generations with no deaths, the population will be
P(1 + c + c² +…+ c^g) = P x (c^g+1 – 1) / (c-1) upon summing the geometric series.

To get the actual population after g generations, we need to reduce this by the number who have died. If the average lifespan is k generations (with k<g), then those who had died by the g^th generation are those in the (g-k)^th generation or earlier. By the same argument as above, this is P x (c^g-k+1 – 1) / (c-1).

Subtracting those who had died in the first (g-k) generations from the total in the first g generations gives those alive after g generations: P x (c^g+1 – c^g-k+1) / (c-1).

This model assumes that on average in each generation families produce c boys and c girls who marry and themselves produce 2c children. Childless people are not counted in this model. This does not affect the growth rate, but an estimate of the living childless should be added to the formula if the intent is to use it to estimate the total population alive at some specific point.

Questions to Ponder

1. Do you think 10 trillion people is a reasonable or unreasonable estimate for the world’s population at the Great Flood? Why?
2. What would you estimate the world population to be at Noah’s Flood? Why?

Share your thoughts on these questions in the comments below. It could encourage or help another reader.

Soli Deo Gloria.

Read the prequels in this series on Population Growth:
1. Population Growth – Could Noah Fill the Earth?
2. Population Growth – Israel in Egypt
3. Population Growth – Challenge to Evolution

Read the sequel:
5. Population Growth – Is 10 Trillion Flood Deaths Reasonable?

See these related articles I’ve written on Noah, the Ark, and the Flood:
Noah’s Flood—Key to the Past
Noah’s Flood—A Global Event
Noah’s Ark Replicas
Noah’s Ark Found?
Earthquakes, Tsunamis, Volcanoes, & Noah’s Flood
Rebuilding Noah’s Ark
Ark Encounter Park
Noah’s Ark Model in Holland
Noah’s Ark
Noah’s Ark Found? (with video)
1. Rebuilding Noah’s Ark – Intro
2. Rebuilding Noah’s Ark – Kentucky Governor (with YouTube videos)
3. Rebuilding Noah’s Ark – How Big?
4. Rebuilding Noah’s Ark – Ark Encounter video
5. Rebuilding Noah’s Ark – Ark Encounter Park
6. Rebuilding Noah’s Ark – Location (with maps)
7. Rebuilding Noah’s Ark – Funding
8. Rebuilding Noah’s Ark – Facing Opposition
9. Rebuilding Noah’s Ark – Ham Debates Lynn (with video)
10. Rebuilding Noah’s Ark – What Would Noah Think?
11. Rebuilding Noah’s Ark – Tour the Dutch Ark (with video)
Dinosaurs on the Ark?
Tsunami Videos and Noah’s Flood
Earthquakes, Tsunamis, Volcanoes, & Noah’s Flood
USA TODAY features Noah’s Ark
Marilyn Monroe and the Age of the Earth
Wallenda, Niagara, & Noah’s Flood (with video)
Mystery of Noah’s Flood (with videos)
Leftover from Noah’s Flood?
Noah, the Movie (with videos)
The Truth about Noah
Meet the Real Noah (with video)
Could Noah Fill the Earth?

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©William T. Pelletier, Ph.D.
“contending earnestly for the faith”
“destroying speculations against the knowledge of God”
(Jude 1:3; 2 Cor 10:4)
Wednesday June 18, 2014 A.D.

In the six hundredth year of Noah’s life, in the second month, on the seventeenth day of the month, on the same day all the fountains of the great deep burst open, and the floodgates of the sky were opened. And the rain fell upon the earth for forty days and forty nights. On the very same day Noah and Shem and Ham and Japheth, the sons of Noah, and Noah’s wife and the three wives of his sons with them, entered the ark, they and every beast after its kind, and all the cattle after their kind, and every creeping thing that creeps on the earth after its kind, and every bird after its kind, all sorts of birds. So they went into the ark to Noah, by twos of all flesh in which was the breath of life. And those that entered, male and female of all flesh, entered as God had commanded him; and the LORD closed it behind him. Then the flood came upon the earth for forty days; and the water increased and lifted up the ark, so that it rose above the earth. And the water prevailed and increased greatly upon the earth; and the ark floated on the surface of the water. And the water prevailed more and more upon the earth, so that all the high mountains everywhere under the heavens were covered. The water prevailed fifteen cubits higher, and the mountains were covered. And all flesh that moved on the earth perished, birds and cattle and beasts and every swarming thing that swarms upon the earth, and all mankind; of all that was on the dry land, all in whose nostrils was the breath of the spirit of life, died. Thus He blotted out every living thing that was upon the face of the land, from man to animals to creeping things and to birds of the sky, and they were blotted out from the earth; and only Noah was left, together with those that were with him in the ark. And the water prevailed upon the earth one hundred and fifty days. (Genesis 7:11-24)