# Noah and repopulating the earth **URL:** \ **Category:** Factual Questions\ **Created:** [July 27, 2001, 3:16pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974 "2001-07-27T15:16:08Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![jharding](https://avatars.discourse-cdn.com/v4/letter/j/e480ec/32.png) [@jharding](https://boards.straightdope.com/u/jharding)\ **Post date:** [July 27, 2001, 3:16pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974/1 "2001-07-27T15:16:08Z")
My question is one of mathematical probability rather than a debate on the veracity of the Noah’s Ark story. However, I recognize the immense overlap here and should this question be more appropriate in GD, then my apologies beforehand. I lifted the following statement from a Creationist website and something seems sketchy about the math used. Any help on how this is wrong or at least improbable? > [@](#): > > \*\*The world’s present population of approximately five billion people, likewise, could easily have been developed in approximately 4000 years. An average annual growth rate of 1 2% (only one-fourth the present rate), or an average family size of only 2.5 children per family, could easily accomplish this. \*\* ---
**Author:** ![The\_Hamster\_King](https://avatars.discourse-cdn.com/v4/letter/t/8edcca/32.png) [@The\_Hamster\_King](https://boards.straightdope.com/u/The_Hamster_King)\ **Post date:** [July 27, 2001, 3:55pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974/2 "2001-07-27T15:55:06Z")
Nope, the math is okay. An annual growth rate of just 1.0% means that you’ll double your population every 70 years or so. 4000 / 70 = 57 doublings. 2^57 is way more than 5 billion. The average family size is a little harder to work with. You also need to know the average age that people are having children to calculate growth rates. An average family size of 2.5 means that you’ll double your population every three generations. Even with the very conservative estimate of three generations a century, you still get 40 doublings. 2^40 is still way more than 5 billion. Of course, all this does is prove that it’s theoretically possible to repopulate the globe in a few thousand years. It’s not like the archeological evidence supports a wave of new human settlements radiating out from the Holy Land 4000 years ago. It also doesn’t address the question of whether 4000 years is enough time to create all the genetic diversity that we witness in the world today. If the world really was repopulated by a small group of survivors 4000 years ago we should all look a lot more alike than we do. ---
**Author:** ![Ike\_Witt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ike_witt/32/283_2.png) [@Ike\_Witt](https://boards.straightdope.com/u/Ike_Witt)\ **Post date:** [July 27, 2001, 4:03pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974/3 "2001-07-27T16:03:04Z")
If the Earth is only 6000 years old +/- as the bible claims, than in the 2000 years before the flood there must have been 2.5-3 billion people on the planet (going by the logic of the creationists). So, out of 2-3 billion people, Moses was the only good one? Too me, it looks like God killed a bunch of innocent people. ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [July 27, 2001, 4:14pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974/4 "2001-07-27T16:14:13Z")
From a population of eight to a population of 6 billion in the space of 4,400 years requires an annual net growth rate of only 0.47%. (8×1.0047[sup]4000[/sup]=6×10[sup]9[/sup]) The current net growth rate is somewhere around 2% per year. However, what with disease and starvation and such, the actual growth rate in ancient times was much, much, lower. Ther net growth rate between A.D. 1 and A.D. 1650 was only 0.005%, an order of magnitude lower than that which would be necessary for Noah to be the ancestor of us all. ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [July 27, 2001, 4:30pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974/5 "2001-07-27T16:30:24Z")
I meant: 8×1.0047[sup]4400[/sup]=6×10[sup]9[/sup] I should note that when there are a lot of resources and few people (as presumably would be the case with Noah after the flood), pre-modern populations could grow very fast. For example, the population of Europe recovered from the Black Death much faster than long-term growth rates would predict. ---
**Author:** ![toadspittle](https://avatars.discourse-cdn.com/v4/letter/t/c0e974/32.png) [@toadspittle](https://boards.straightdope.com/u/toadspittle)\ **Post date:** [July 27, 2001, 5:32pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974/6 "2001-07-27T17:32:36Z")
> [@](#): > > \*Originally posted by bibliophage \* > I should note that when there are **a lot of resources** and few people (as presumably would be the case with Noah after the flood) I was about to dispute this “lot of resources” comment (assuming they don’t decide to slaughter most of the ark’s menagerie for food)–after all, everything has been under water and flood- and storm-ravaged for a long time. All of the plants should be dead, too = no crops. But then I remembered the fish. I guess there would be plenty of them to catch (and many that might be trapped in newly-created inland water bodies by receding waters, etc.). Oh well. ---
**Author:** ![Lucky](https://avatars.discourse-cdn.com/v4/letter/l/e9c0ed/32.png) [@Lucky](https://boards.straightdope.com/u/Lucky)\ **Post date:** [July 27, 2001, 6:15pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974/7 "2001-07-27T18:15:30Z")
Which fish? The salt water or the fresh water? ---
**Author:** ![manhattan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/manhattan/32/7_2.png) [@manhattan](https://boards.straightdope.com/u/manhattan)\ **Post date:** [July 27, 2001, 6:33pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974/8 "2001-07-27T18:33:15Z")
So **adam yax** and **Lucky** , was there some part of the OP’s statement that “(m)y question is one of mathematical probability rather than a debate on the veracity of the Noah’s Ark story.” that you missed? ---
**Author:** ![xizor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/xizor/32/102_2.png) [@xizor](https://boards.straightdope.com/u/xizor)\ **Post date:** [July 27, 2001, 6:39pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974/9 "2001-07-27T18:39:14Z")
> [@](#): > > \*Originally posted by adam yax \* > **So, out of 2-3 billion people, Moses was the only good one?** Just to clarify, **Noah** was the one with the arc and the flood, **Moses** did the 10 commandments. ---
**Author:** ![Max\_Torque](https://avatars.discourse-cdn.com/v4/letter/m/e9bcb4/32.png) [@Max\_Torque](https://boards.straightdope.com/u/Max_Torque)\ **Post date:** [July 27, 2001, 7:15pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974/10 "2001-07-27T19:15:50Z")
Something to consider in an old article from my collection, which as I recall comes from the book _In The Beginning_ by Dr. Chris McGowan: > [@](#): > > ``` > "Creationists, having been so critical of radiometric dating, would surely have some rigorous method for arriving at their young age for the earth. How do they do it? They use such infallible methods as assessing how long it has taken for our [world] population to grow from the original nuclear family of Adam and Eve! Dr. Morris calculated that if Adam and Eve, and subsequent couples arising from their union, had only between two and three offspring, the present world population could have been reached in only one hundred generations. Assuming a generation time of forty years, which is very reasonable, this represents only four thousand years. Applying similar logic to the evolutionists' 1-million-year estimate for the history of man (which is probably very conservative), he arrives at a number of such astronomic size that it exceeds the number of electrons in the universe. Impressive stuff! > > There is nothing wrong with Dr. Morris's arithmetic, but his biology is off base. Now flies, as we all know, lay thousands of eggs and their generation time is measured in weeks, not years. We should therefore expect to be over our heads in the things by now, but we are not, and the same is true for other animals. The reason is that populations are kept in close check by competition, especially for food; by disease; by adverse climactic conditions; and, it has been suggested, by internal regulatory mechanisms. Population numbers do get out of order at times, and then we see population explosions - swarms of locusts, flocks of lemmings, and the like - but over the long term, animal populations remain fairly constant. The notable exception is our own species, and the reason we are experiencing a population explosion, a fairly recent phenomenon, is that we have learned to eliminate competition and to overcome disease. We do not share our crops with any of the other species, not with rabbits (we all but wiped them out with myxomatosis in the fifties), or with insects (our new pesticides are notoriously deadly), and we do not allow other plants (weeds) to compete with them. This, of course, is true only in the 'developed and developing world'; primitive cultures are nowhere near as successful in competing with nature. This reflects in their small population sizes and also in the numbers of tribes that have become extinct. While many of these extinctions have probably been caused by interference from 'civilized' peoples, the fact that they did occur reflects such tribes' precarious tenure on the earth. Consider for example, the Fuegians, living in isolation on the bleak island of Tierra del Fuego, off the southern tip of Argentina. When Darwin visited the island in 1832 they numbered in the hundreds, but by the end of that century they were all but extinct." > > ``` ---
**Author:** ![jharding](https://avatars.discourse-cdn.com/v4/letter/j/e480ec/32.png) [@jharding](https://boards.straightdope.com/u/jharding)\ **Post date:** [July 27, 2001, 7:37pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974/11 "2001-07-27T19:37:42Z")
To bibliophage and Pochacco, that’s the kind of info I was looking for–thanks. Also, thanks to manhattan for keeping a tight reign on what I hope is a pretty short and simple thread. ---
**Author:** ![KeithB](https://avatars.discourse-cdn.com/v4/letter/k/48db29/32.png) [@KeithB](https://boards.straightdope.com/u/KeithB)\ **Post date:** [July 27, 2001, 9:56pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974/12 "2001-07-27T21:56:47Z")
Here is an interesting quote from talk.origins: Quote: 7. Human population growth Many species have had their populations measured over time. While the short-term growth rate can vary wildly (due to environmental factors), the long-term growth rate is always very close to zero. Usually a limited food supply keeps populations at equilibrium. Until humans invented agriculture (which breaks that constraint), there is reason to expect that we were subject to the same limiting forces as other animals. Still, let’s check the implications of Bob’s 6000 years @ 0.36% growth: Start with 2 people at 4000 BC. By 2500 BC, the population is 440. Let’s place half the earth’s population in Egypt, and discount the elderly, women, and children. The Great Pyramid must have been built by about 40 men, who quarried and moved 2,300,000 blocks (up to 50 tons in weight) in under 40 years’ time. (4 blocks/man-day. Must be non-union labor.) About 20 men must have built the first pyramid some 200 years earlier, while the other 20 able-bodied men on Earth were constructing fortified cities in Mesopotamia. In 3700 BC, both able-bodied men on Earth must have been quite busy constructing impressive civilizations in Crete, Mesopotamia, the Indus River valley, and other sites. Obviously, Bob’s uniform approximation doesn’t work. To account for the population in 3700 BC, he will have to drop his rate to 0.16%. The rate from 3700 BC to 1 AD will be about 0.06%. Bob will have to admit to a rate over 2/3 of recorded history that is 96% of the way to equilibrium from the measured 1971-1975 values. I don’t understand how he can find equilibrium to be “unjustified” when he is suggesting rates about the same distance from the measured ones for his own scenario. The growth rate is known to vary greatly over short periods of time; it is noticeably influenced by factors missing from Bob’s oversimplification; and it is not that far from equilibrium. Bob should have known this method was unreliable when he plugged in current growth rates and “proved” Last Wednesdayism. I don’t understand why he felt justified in pulling a lower rate out of a hat; I’d have discarded the method as unreliable. Bob thought this method wouldn’t support long histories when applied to other creatures. I approximated houseflies, and calculated their origin to be in 1982 with similar growth rates (probably too low). Bacteria must have been created no earlier than 1988. Clearly, these “simple” assumptions can vastly underestimate how long a species has been around. End Quote This is plucked from the middle of a debate. Ask your creationist friend to calculate how many people were around for the Exodus, and how that agrees with the Bible. (To find this quote go to the index in [http://www.talkorigins.org](http://www.talkorigins.org) and look for “population”.) ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [July 27, 2001, 10:00pm UTC](https://boards.straightdope.com/t/noah-and-repopulating-the-earth/73974/13 "2001-07-27T22:00:44Z")
> [@](#): > > The world’s present population of approximately five billion people, likewise, could easily have been developed in approximately 4000 years. An average annual growth rate of 1 2% (only one-fourth the present rate), or an average family size of only 2.5 children per family, could easily accomplish this. Sure, _with simplistic assumptions_ this is possible. But, amongst other things, it turns on the fact that you’re relying on an exponetial increase and, while such increases become _very_ fast, they start off slow. You wind up claiming that about two dozen people completed the pyramids in Egypt by themselves. And built Stonehenge on their weekends.