Dennis Bradford

389 Posts



In terms of human population, it is not obvious why we are so lucky.

There are about 7 billion humans alive today. Although that may seem like far too many for the limited resources available, the future should not get much worse in the sense that, by the end of this century, it is supposed to level off at about 10 billion. In the sense that scientists may not understand it fully, that’s nothing except luck. Our immediate future could have been expected to be far worse.

One of the fundamental facts of modern history is this fact about population: humans tend to have smaller families as they become wealthier.

Why? Nobody knows!

Due largely to the consequences of the second agricultural revolution, Thomas Malthus’s well-known predictions about population disaster have not come true in the short run.

Will they come true in the long run? Apparently not.

This, though, seems not to make any biological sense. Typically, when their circumstances improve, species increase their reproductive rate rather than decreasing it. Why don’t humans?

Nobody knows the explanation for this human demographic transition.

The standard explanation is that humans shift to a different reproductive strategy.

The biological imperatives are to survive and reproduce. Ecologists distinguish two population strategies, namely, “r-selection” and “k-selection.”

Especially if a local environment is characterized by high infant mortality, r-selection is favored. This strategy is to be like trees: produce many offspring and invest few resources in each.

The other strategy, k-selection, is to produce fewer offspring and invest more resources in each. The idea is to produce better offspring by nurturing them so that those offspring will likely have more success when it comes to competition for survival and reproduction. This should actually produce a greater number of offspring over the generations compared to r-selection.

The standard explanation is that the population shifts as humans become wealthier and have smaller families because k-selection becomes preferred to r-selection. There should be, according to this explanation, an evolutionary advantage for k-selection compared to r-selection over the generations. This prediction is not only testable, but it also makes sense.

After all, imagine two families who are in similar circumstances except that one family has fewer offspring than the other. Presumably the family with fewer children will tend to produce offspring with greater competitive advantages compared to the offspring of the other family. Those offspring may, for example, get more help with their schoolwork and, so, get into better universities and, so, get better jobs and have higher lifetime incomes that will enable them, in turn, to spend more resources nurturing their own offspring. The advantages should multiply down the generations.

That seems to be true as far as it goes. However, Dr. Anna Goodman and her colleagues have recently found that these more favored offspring do not reproduce more offspring than those other offspring.

In fact, they tend to produce fewer offspring! The evolutionary advantage for k-selection disappears and becomes an evolutionary disadvantage in terms of the rate of reproduction. This is best explanation for the most important recent historical fact about human population.

It is also as initially puzzling as it is unanticipated. What could explain it?

Obviously, it is incomplete. There must be at least one missing factor.

It’s likely that some recent historical developments have been overlooked. For example, rates of child mortality have recently declined due to such factors as improved public health. Education has become freely available to more children. K-selected males are no longer encouraged to form harems.  Such developments may have diminished the disadvantages of being r-selected.

If so, this is very interesting. It suggests that there is a mismatch between our biological inheritance and our present circumstances.

An analogy is to the current epidemic of obesity (and related diseases). Nearly all of our genetic development occurred prior to the first agricultural revolution that began only about 12,000 years ago. Especially after the second agricultural revolution about a century ago, this has left us with a mismatch between our Stone Age bodies and our actual historical circumstances in the Anthropocene.

We have shifted from getting most of our energy from natural fats and proteins to getting most of our calories from carbohydrates, which, when digested, all become sugar. Had we continued to eat and to move more like our successful Stone Age ancestors we would not have become so obese.

(The cure for obesity is, therefore, easy to understand. Since we cannot change our genetic inheritance, the only sensible option is to return to eating and moving much more like our successful ancestors. For a lot more on this, see the posts in the Physical Well-Being category of this blog as well as my Real Overeating Help and lasting-weight-loss.)

Obesity is harmful to obese individuals. It diminishes their ability to survive and reproduce.

Smaller families, however, are not harmful to individuals. That is why we have been very lucky when it comes to population.

If smaller families had been harmful to individuals, instead of anticipating a leveling off of human population in the next few decades, we would have had to anticipate a continuing rise in human population leading to Malthusian doom.

As bad as the environmental damage is that we billions of humans are already doing, it could have been much worse. Yes, we are already beginning to experience ecological disaster, but we are also very lucky.

[A footnote from the history of philosophy that relates to thinking seriously about population: think a bit more about the children from the two families imagined before. If you were a child from the family with more offspring and, so, through no fault of your own, had less favorable nurturing than a child from the family with fewer offspring, would that be fair to you? Karl Marx thought not. In terms of the quality of your life, you’d be getting a worse deal than necessary.

This inequality was a motivation behind his arguments about how to reduce both exploitation and alienation. It does not, of course, follow that his arguments were sound. It’s worth pointing out, though, one of the chief benevolent impulses motivating them.

We do and should want all children to have an equal opportunity — and population considerations are relevant to practical proposals designed to foster that morally laudable goal.]


As always, if you know someone who might benefit from reading this, please pass it along.

RECOMMENDED POSTS: The Anthropocene and The Second Agricultural Revolution.

RECOMMENDED READING: “The Demographic Transition” in The Economist (1 Sep 12) and The Marx-Engles Reader (Robert C. Tucker, ed; 2nd ed.).

1 thought on “Population

  1. BigTuna

    Interesting ideas in this post. From my own experience and family history I can only say that my parents had less children then their parents because my grand parents didn’t believe in using birth control!
    My guess is that using birth control is more widely accepted today then 50 years ago. I wonder if wealthy families have less kids nowadays because they simply want less kids.

    02/10/2012 at 2:17 pm

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