POPULATION RATES AND THE AGE OF THE EARTH
by Lenny Flank
(c) 1995
One argument for a young earth which is often repeated in creationist literature involves the rate of population growth. In this argument, the creationists propose to determine the age of the earth by calculating backwards from current human population levels, to determine how long it would take to get back to an original pair of humans (presumably Adam and Eve).
Morris presents his argument in mathematical form (so it sounds nice and scientific):
"Assume an initial population of two people, the first parents. Assume they produce a total of 2c offspring, c boys and c girls, who then unite to form c families. Each of these families also has 2c children, meaning there will be 2c^2 children in the second generation. These form c^2 families, and then 2c^3 children in the third generation, and so on. In the nth generation, there will be 2c^n individuals. If we assume, for simplicity, that only one generation is alive at any one time, then the world population at the nth generation will also be 2c^n people." (Morris, Scientific Creationism, 1974, p. 167)
Morris then assumes that there have been 100 generations since the first pair 40 years per generation for 4,000 years), and that therefore the average family size must have been 2.46 children. "In other words," says Morris, " an average population growth of 1/2 percent per year would give the present population in just 4000 years. This is only one-fourth the present rate." (Morris, Scientific Creationism, 1974, pp 167-168)
Thus, Morris concludes, modern population figures show that the earth had only two people approximately 4,000 years ago. On the other hand, Morris goes on to show, if we assume these same figures for a period of one million years, we would have more people alive today than the number of electrons in the universe. "It is obvious from the above analyses," concludes Morris, "that the creation model of human chronology fits the facts very well and is, in fact, quite conservative." (Morris, Scientific Creationism, 1974, p. 168) Thus, the world's population figures demonstrate that the earth is only 4,000 years old and cannot be even one million years old.
While Morris's mathematics are impeccable, the reasoning behind his argument is shoddy at best. There is no reason to "assume" that there have been 100 generations in human history, or that these generations were 40 years apart, or that the first pair of humans lived 4000 years ago--other than the creationist assumptions that the Biblical Adam and Eve lived around that time. The assumed growth rate of 1/2 percent per year also has no basis in reality and was merely pulled out of thin air to produce the desired "age". There is no reason to assume a constant population growth throughout human history, and plenty of reasons to assume otherwise. And Morris ignores completely the fact that a large proportion of humans would die before having any children at all--through disease, accident, war etc. Instead, he assumes (without any justification) that everyone lives to reproduce between two and three children per family.
Morris also seems to somehow forget that his "creation model" binds him to the conclusion that there was a global flood several thousand years after his "original couple", and that all current humans are descended, not from Adam and Eve, but from Noah and the seven people with him on the Ark. But for some reason, Morris's population model does not lead us back to a population of eight people in the second millenium BC.
However, let us accept Morris's figures for the moment, and approach this problem from the other end. If we assume that Adam and Eve lived 4000 years ago and that the average population growth per year was 1/2 percent, how many people would we have had after, say, 2000 years? A quick calculation shows that we would have fewer than 1,000 people, worldwide, by the time the pyramids were built in 2,000 BC. That means that the entire population of the earth, under Morris' model, would have been required to quarry and move the stones used to build the pyramids. But if all these people were constructing the pyramids, then who was living in all the cities whose ruins we find scattered all over the world? Who was populating China, the Indus Valley and North America in 2,000 BC?
Finally, let us apply Morris's logic to the population of another species, say, houseflies. Houseflies have a generation time of just a few weeks, and each female is capable of laying several hundred eggs per generation. At that rate, the current population of houseflies would be reached in less than a decade, if we assume that every female fly lived for one month and produced a clutch of 100 eggs, and that each resulting female also produced a clutch of 100 eggs. Thus, given the current population of houseflies, it is impossible for the earth to be more than ten years old. (Of course, we are assuming here that every housefly reaches maturity and reproduces before it dies--the same assumption that Morris makes regarding the human population.)
Contrary to Morris's fanciful assumptions, there is no reason to believe that the global human population has been increasing exponentially, and good reason to believe that it was in fact stabilized by environmental factors (just like the housefly population has been) throughout most of human history, right up until the agricultural and industrial revolutions which have allowed population growth rates to climb sharply. Morris's population argument is nothing more than an exercise in story-telling, and in it we see the basis for the other stories told by the creationists--selecting a short term trend and then projecting and extrapolating it backwards until it reaches the desired result.