MrDarwin

Well, here's a little problem right here: are these assumptions valid? Has the average age at which people produce a new generation really been 35 years old, in the recent or distant past? I rather doubt it.

Has anybody tried plugging in figures with a slightly different average generation length or number of children produced per couple? (The figure that's actually important is how many children a couple produces in a given amount of time who go on to grow up and reproduce, so fecundity and infant mortality play major roles.)

Doubting Didymus

A larger question: Are ANY of the assumtions in that article valid? A single solitary one?

Strawberry

Thomas R. Malthus did indeed put forth a theory on population growth. His theory is that unchecked population has a tendency to 1) grow exponentially and 2) exceed its food source.

According to the "real" Malthus himself, those numbers are bunk. (Again, doubling at equal increments of time? ROTFL!)

Silent Acorns

Another obvious mistake: the rate of population growth is a function of average lifespan and the average number of children who reach child bearing age per woman. The "average generation length" is irrelevant.

Mageth

This page has some nice graphs of (estimated) world population from @10000 BCE.

Note that from 4000 BCE-1000 BCE the population is estimated to have doubled @ every 1000 years.

The estimated population then doubled from 500 BCE (100m) to 600 CE (200m). (1100 years)

It took another 650 years for the population to double again (1250 CE) to 400m.

And then 550 years for the population to double again (1800 CE) to @813m.

And about 100 years to double again to 1750m (1900).

60 years to double again (to @3b), and then 40 years to reach today's estimated population of 6b.

The facts don't fit too well with the assertions made in the article, do they?

Mageth

Another problem with the geometric doubling. Approximately 30 doublings between 3500BCE-2000CE would make "T" @183 years.

Assuming you started with 2 people at 3500 BCE, world population today with 30 doublings would be 2^30 = @1.073 billion. So you need a couple of more doublings in there...(32.5 doublings would give @6billion in 2000 CE).

Overlooking that, 3500/183 = @19 doublings from 3500 BCE to 0 CE. 2^19 is only 524,288! Even if you allow 32.5 doublings, that would still only be @1.7 million total population at 0 CE.

Not to mention the fact that world pop would have hit 3 billion in the early 19th century, rather than 1960...

MrDarwin

I don't have time to do it myself right now, but could somebody please plug some different numbers (e.g., average generation time and average number of children surviving to reproduce per couple) into the starting formula of 3 couples (Noah's 3 sons and their wives) at the time the flood supposedly started the world's human population growth from scratch? I'm willing to bet you get wildly different projections of what the world's population should be today, depending on what numbers you pick and choose.

Mageth

Well, if you started out with 8 people 4500 years ago, assuming geometric doubling that would put the doubling time T at @140 years, and world pop at 0 CE at @244k.

Note that with the 5500 year/start with two/double every 183 years, it would have taken @1200 years for the world pop to break 100, and @1800 years for the world pop to break 1000!

Silent Acorns

If we assume an average life span of L years and that the average woman has n children who reach child bearing age then:

death rate = 1/L
birth rate = n/2L

growth rate = birth rate - death rate = (n/2 - 1)/L
doubling time = log(2)/log(1+growth rate)

Note: this assumes a large population and ignores infant mortality.

starting with a reproductive population of 6 in 3500 BC:

if L = 70 years and n = 3 kids then current pop = 600 000 trillion
if L = 50 years and n = 3 kids then current pop = 5 trillion trillion
if L =136 years and n = 3 kids then current pop = 6 billion
if L = 70 years and n = 2.525 kids then current pop = 6 billion

Note the incredible sensitivity to "n" and "L". There is no reason to believe that these values have stayed the same for 5000+ years.

Hope this answers your question MrDarwin.

<edited to note that the above model also assumes that the disribution of ages is even. In a growing population it will be skewed towards the young and as a result the death rate will be lower than 1/L and the birth rate could be higher or lower than n/2L.>

SanDiegoAtheist

And of course, it would result in the Pyramids having been constructed by ~20-30 people, give or take a doubling or so.

Boy those were some hard workers.

Cheers,

The San Diego Atheist