Population Growth

(from Musings and Rants 1985-2016, Marcus Everett 2017, CKCPC3 Publishing, p173, written in 2007)

Several years ago a friend was telling me about a book she had read about the Blue Crab. The life cycle of the Blue Crab begins in bays and marshes along the East Coast from the Mid-Atlantic States to the Gulf States. The mature female can only mate during a 'shed', when she discards an old shell and before the new shell hardens. If she is fertilized during this event, under her 'apron' she will grow a large egg mass, which looks like a big orange sponge. She will then make her way to the inlet of the bay where she has been living to release her eggs into the outgoing tide.

The eggs hatch and the baby crabs spend the first half of their life at sea. When they reach about half of their adult size, they return to the bays to mature and mate. The question of interest, then, is what percentage on average of the thousands of eggs released by a female make it back to successfully mate?

Most people would guess that the percentage is small, and they would be right. But it is possible to be more precise. For a stable population, each successfully breeding female must, on average, produce exactly one successfully breeding female. If the average success rate is greater than 1, the population will grow exponentially; if the rate is less than 1 it will decrease exponentially. An average success rate of 2 would result in the population doubling every generation, a success rate of 0.5 would result in it halving every generation.

One might ask about the poor males, but as long as the survival rate of males is sufficient to fertilize a sufficient number of females, the population growth rates depend almost entirely on the success rates of the females.

The above consideration holds for any sexually reproducing species, whether it's crabs, birds, whales or humans. If the average female success rate differs from 1, the population will either grow or decay exponentially. This fact has rather profound implications for modern humanity.

For most of known human history, the long-term female success rate has been greater than 1, but only barely. Estimates of population growth over the 10,000 years before about 1700 put the average success rate, assuming 20 years for a generation, at about 1.01. This rate of success implies that each generation was about 1% larger than the previous, and that the population doubled about every 1500 years. Wars had little effect, since as was pointed out above only a sufficient number of males are required. (This fact is borne out by the baby boom after WWII - losing a half million males didn't even keep the growth rate flat!) Disasters that affect both sexes cause a short-term stutter, but usually this just makes it easier for the next generation or so to make up lost ground.

The problem is that, over the last 200 years, the industrial revolution together with modern medicine and agriculture has greatly increased the survival rate and therefore the potential female success rate. I say potential rate, since some cultures have voluntarily reduced the rate even below 1. China, in fact, has recently implemented a one child per couple rule which, together with a cultural bias against female offspring, has apparently resulted in an effective female success rate of something like 0.4. This is a drastically low rate, and will result in economic and social chaos in even one generation if not eased. A more reasonable target might be one female child per couple.

Unfortunately, much of the third world is reproducing at a rate significantly greater than one. The world population growth rate is currently such that the population has been doubling about every 35 years. If we assume a 20-year generation, this is an average success rate of about 1.5, or in other words each generation is about 50% larger than the previous. The third world rate must be considerably higher than this since the industrial nations (minus certain minority groups) now have rates lower than 1. If the human density on the planet were still insignificantly small, this might be a good thing. However, we are already depleting our natural resources such as fossil fuels, water, oceanic fish stocks and everything else you can think of. Our waterways are polluted, our air is polluted, and there MAY be some increase in global warming over and above the interglacial effect due to human activity such as deforestation and production of excess carbon dioxide and methane.

What is depressing is that, although there seem to be unlimited cries for more laws against SUVs, coal fired power plants, etc., there is never a discussion or even a suggestion about reducing the human population. Doing so would not only help solve all these problems, but may well be the only long-term solution. No laws and no amount of technology can long compensate for the current rate of exponential growth of the human population on Earth. We must control our numbers or face the inevitable catastrophic reduction that reality will impose upon us. This fact especially must become a part of any intelligent discussions about subjects such as global warming, as well as contraception and abortion.

It should also be noted that, although the human female success rate is considerably greater than 1, the blue crab is obviously suffering a current female success rate significantly below 1. The friend that I referred to above recently paid over $60 a DOZEN for jumbo crabs at a restaurant near Baltimore. H. L. Mencken would be aghast.