Definition of Natural Increase

A Definition of Natural Increase; the Contextual Meaning of "Natural"

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The term "natural increase," refers to population increases. So far, so good. But as economists use the term, the result could be negative. And who's to say what's natural?

The Term Natural Increase Defined

"Natural increase" is a term used in economics, geography, sociology and population studies. In simplest terms, it is the birth rate minus the death rate. Birth rate in this context almost always refers to the annual number of births per thousand in a given population.

Death rate is defined the same way, as the annual number of deaths per thousand in a given population.

Because the term is always defined in terms of a given rate of birth minus a given rate of death, "natural increase" is itself a rate, i. e., the rate of net increase in births over deaths.  It is also a ratio, where the birth rate in a specified period is the numerator and the death rate in the same period is the denominator. 

The term is often referred to by its acronym, RNI (Rate of Natural Increase). Note also that an RNI rate can be negative if a population is in decline, i. e., is actually a rate of natural decrease. 

What is Natural?

How population increases acquired the qualification "natural" is information lost over time, but probably originated with Malthus, the early economist who first proposed a math-based theory of population growth in his Essay on the Principle of Population (1798).

Basing his conclusions on his studies of plants, Malthus proposed an alarming "natural" rate of population growth, proposing that human populations increased exponentially -- meaning that they double and redouble to infinity -- in contrast the arithmetic progression of food growth.

The difference between the two growth rates as Malthus proposed it, would inevitably end in disaster, a future where human populations would starve to death.

To avoid this disaster, Malthus proposed "moral restraint," that is, the humans marry late in life and only when they clearly have the economic resources to support a family.

Malthus study of natural population growth was a welcome investigation into a subject that had never before been systematically studied. Essay on the Principle of Population remains a valuable historic document. It turns out, however, that his conclusions were somewhere between "not exactly right," and "totally wrong." He predicted that within 200 years of his writings the world population would have increased to about 256 billion, but that increases in food supply would then support only nine billion. But in the year 2,000, the world population was only a little over six billion. A significant portion of that population was underfed and starvation remained and remains a significant world problem, but the starvation rate never approached the drastic 96 percent starvation rate Malthus proposed.

His conclusions "weren't exactly right" in the sense that the "natural increase" Malthus proposed could exist and actually might exist in the absence of factors he didn't take into account, the most significant of them being the phenomenon studied soon after by Darwin, who noted that populations are in competition with one another -- there is a battle for survival going on everywhere in the natural world (of which we are a part) and absent deliberate remedies, only the fittest survive.