In an effort to prove that the Earth is not very old, creationist Henry M. Morris has devised a calculation that is based upon the human population explosion. Using the equation Pn = P(1+r)n, he shows that two individuals present on the Earth in 4300 BC (presumably Adam and Eve) could initiate sustained exponential population growth sufficient to produce the entire estimated global population of year 1800 AD.1 Values used by Morris in this equation are P = 2 (initial population of Earth), Pn = one billion (estimated population of the Earth in 1800 AD), and r = 0.0033 (1/3 of 1% increase per year; estimated per capita global growth rate, 1650 to 1800 AD). He solves for n, obtaining as an answer the value n = 6100 years (prior to 1800 AD). By this calculation, he shows that it is mathematically possible for two individuals who lived about 6300 years ago to have given rise to the entire modem population of the Earth. Although he says nothing about the age of the Earth in this derivation, he cites this calculation in other works as evidence that the Earth itself is not very old.2, 3, 4 Other creationists offer their own version of this calculation, using similar logic and slightly different numbers.6 Even Morris himself tries different numbers in another work.5
The second half of this particular creationist argument is that if humankind had been reproducing at even a minuscule rate (say, r = 0.0001) for a million years or more, the entire solar system would now be crammed with human bodies.5, 6 Therefore, say the creationists, population growth statistics support the view that human beings (and by implication the Earth itself) appeared only a few thousand years ago, while contradicting any possibility that people (and the Earth) have existed for much longer. This creationist argument depends upon the assumption that human numbers must necessarily have been increasing throughout all of a necessarily brief human history, while the evolutionary view assumes that populations of humans and their earlier ancestors have had a zero growth rate (i.e., r = 0) over most of their history.
To understand why the creationists are wrong, consider this example. Suppose that a creationist were studying snowshoe hares, somewhere in Canada in the early 1930's. At that time, the bunnies were multiplying at a per capita rate of about r = 0.57 (57% per year). If that was all that our biologist knew about the rabbits' history and biology, the Morris calculation would enable him to determine that the first two snowshoe hares of all time appeared on Earth in late 1885, during the Cleveland Administration.8 Not only that, but the Morris calculation applied to minks, muskrats, foxes, and lynxes (which were also multiplying at that time) would also place the date of the creation of the Earth and life in the late 1800's. If one accepts that the Cleveland Administration was not the perpetrator of it all, then where are the errors? Here, two major mistakes are involved. First, the creationist in this instance did not use all of the known facts in arriving at his conclusion. Second, he assumed that the entire rabbit history was similar to that of those last few years that he was able to observe. In fact, the hares (and their predators) are known to cycle in abundance. In 1933 their numbers were increasing, but only as the latest in a series of roller coaster ups and downs that can be traced clear back into the 1700's. Over the long haul, r = 0 for the bunnies, a fact that would not be evident to an observer who watched them only during the early 30's.
The Morris calculation using human population statistics contains both elements of the "bunny blunder." Facts are ignored, and the assumption is made that all of human history prior to 1650 was characterized by growth like that seen from 1650 to 1800.
Unlike the bunny situation, we have no real knowledge of the true global human population size in medieval and earlier times. Almost all estimates are based on measures of carrying capacities of agricultural land and hunter/gatherer ranges, estimates of labor forces needed to construct various public works, and other indirect measures of population sizes.9 These estimates, many of which give world populations of about 1/4 billion at the time of Christ, are among the facts ignored by Morris.1 Others include the fact that humans must be a glaring exception to the usual situation in nature, if humans have experienced a high positive value of r throughout Earth history while all other species have had growth rates of approximately zero. Plagues and famines, also ignored by creationists, have decimated human populations with dreadful regularity over the ages. Where they have exerted their effects, population growth could not possibly have been rapid or even positive. When bubonic plague entered Europe during the mid-1300's, for example, nearly a quarter of the entire population died within one year, and European population actually declined for a century or two thereafter.10 Such episodes have been so common throughout human history that they can be considered to be the rule, rather than exceptional occurrences.11
Finally, even the limited numerical data, which are not favorable to the creationists' argument, are ignored. In St. Botolph, a parish of London from which unusually complete burial and christening records have survived to the present day, the death rate slightly overshadowed the birth rate between 1558 and 1625 AD, and drastically overshadowed it during the plague years 1563, 1593, 1603 and 1625.12 Thus, r was always slightly negative during this period, and was drastically negative during the epidemic years.
Thus, although the "facts" in the human case are not as firm as in that of the snowshoe hares, nevertheless all of them point toward the same conclusion. That is, human population growth was probably negative, zero or near zero over much of times past. Only by ignoring these contrary indications and by assuming that the growth rate of the pre-Industrial Revolution years was somehow typical of all of human history can creationists arrive at the conclusion that two human individuals living in 4300 BC could in actual reality have produced the entire world population of today.
In addition to committing the "bunny blunder" in their calculation, creationists make other errors in their use of population statistics as an indicator of the age of the Earth. For example, there is no scientific evidence that world population once consisted of only two people (or even a very few). And even if it could be shown that there were only two (or a few) people present on the Earth a few thousand years ago, this is not the same as showing that these were the first people of all time. They could have been the survivors of a previous cycle (or a thousand previous cycles) of population boom followed by epidemic bust. And even if they were the first people of all time, this still says nothing about the age of the Earth. The Earth could not be younger than those individuals, but how much older it is, whether it be a few days or 4 billion years, must be demonstrated from other evidence.
As if these fatal flaws were not enough, Morris's calculation has ridiculous implications. For example, if we assume for the moment that human numbers really did grow exponentially at a per capita rate of r = 0.0033, starting with two people in 4300 BC, then we can calculate the world population of year 2500 BC. By Morris's calculation, that number is 750 individuals. If Egypt, with about 1% of the Earth's land surface area, also had 1% of its population, then about eight people must have lived in Egypt at that time. However, the Great Pyramid of the Egyptian king Cheops was built in about 2500 BC.13 If the creationists are right, then the Pyramid was built by eight people. In fact, suppose that the entire population of the Earth lived in Egypt at that time. Half of the 750 souls were women (who I don't think worked on the Pyramid); half of the males were children (ditto) and a few exalted characters (Cheops himself and his assorted advisors) undoubtedly convinced the others that nobility should not have to haul heavy limestone blocks. That leaves about 150 able-bodied men to quarry 2,300,000 blocks (ranging from 2.5 to 50 tons in weight), haul them to the construction site and raise the 480-foot Pyramid. Does anyone who has seen this colossal monument believe that 150 men could have built it? Yet that is what Morris, through the magic of his calculation, must boldly assert.
World history prior to 2500 BC, in the Morris scenario, becomes even more remarkable. Six pyramids, some comparable in size to the Great Pyramid, were built at nearby sites within the previous 200-year period (as were numerous accessory causeways, temples, etc.).14 The parents and grandparents of the 750 people at the Great Pyramid site must have built them, at the rate of one every 33 years. Their numbers (which, recall, constituted the entire human population of the Earth) were fewer then—only about 300-400 souls—and they were distracted by the need to perform a fast migratory quick-step over to Mesopotamia to build (and abandon) a number of fortified towns that appeared at about that time. The action was even more frenzied in earlier centuries. World population in 3600 BC, as calculated by the Morris equation, was 20 people. A century earlier, in 3700 BC, it was 14 people. And a century earlier than that, it was 10 people. So, in the Morris scenario, a world population of one or two dozen people must have rushed back and forth between Crete, Mesopotamia, the Indus River valley, and other sites of ancient civilization, energetically building and abandoning enough cities, irrigation works, monuments and other artifacts to leave us with the mistaken impression that millions of people populated the ancient world.
To summarize, then, the creationist calculation of the age of the Earth, based upon population statistics, has the following flaws:
- It ignores many indications that human per capita growth rates were zero or negative throughout much of human history;
- It assumes that growth rates characteristic of the later pre- and early-industrial world were characteristic of human populations throughout all of preceding history;
- It assumes, without evidence, that the entire world population once consisted of two (or a few) individuals;
- It assumes that the Earth is only as old as (or slightly older than) its human occupants;
- It predicts unrealistically small human population sizes for ancient historical times.
In conclusion, it seems appropriate to recall Morris's statement, "The burden of proof is altogether on evolutionists if they wish to promote some other population model."1 It would seem, however, that it is the creationists who need to explain why their model, based as it is upon erroneous or unsupportable assumptions and producing laughable perspectives on ancient history, should be accepted in preference to an evolutionary view that fits the facts.