Agriculture and population growth


Jason Collins


September 17, 2012

Over the last few months, I have heard the phrase “agriculture creates excess population” or other words to that effect from several sources. The latest is at Evolvify, where Andrew references Richard Manning and writes:

Agriculture creates excess population. The argument that we need more agriculture to support higher population fails to recognize its inherently circular nature.

While I have some sympathy to the argument about the destructiveness of agriculture for the ecosystems it supplants, I would prefer to frame the argument differently.

If we take the Malthusian model as a description of human history, for most of that history populations were at subsistence level. The constraint on population was the level of technology. Improved technology did not increase living standards as population would simply increase to match the rise in technology (making population density a crude measure of technology). Some populations managed to briefly have higher living standards by imposing society-wide checks on fertility, or through higher death rates due to disease or violence, but subsistence was the norm.

Thus, in hunter-gatherer societies, population was constrained by the technologies available to them. A technology that allowed more game to be caught may briefly raise living standards, but population would soon increase to take advantage of the additional resources. Population could also increase where new land was entered, such as the entry of humans into the Americas 12,000 years ago.

With the advent of agriculture, the new technology allowed even higher populations. However, up to the 18th century, population generally grew in line with technology and most of the population remained at subsistence levels. New land would at times be opened up to agriculture with accompanying population growth, such as with the European settlement of the Americas, but the Malthusian constraint remained.

Thus, it is not agriculture in itself that creates excess population. The very nature of the Malthusian state - which was the state of human populations for most of their history - is excess population.

Then, around the time of the Industrial Revolution, incomes started to grow faster than population. Populations where this occurred were now able to obtain incomes above subsistence. The twist in the tail was that those with higher incomes lowered their fertility, allowing per person income to grow even faster. So, although population has grown quickly since the Industrial Revolution and on the back of agriculture, it has not grown as fast as the loosened Malthusian constraints would allow. In that sense, there is not overpopulation. We could even argue by this measure that many parts of the world have never been less crowded.

One obvious response is to ask whether the current use of land for agriculture is destroying future capital. Is agricultural productivity ephemeral, as today’s income is coming at the cost of income at the future? In that scenario, it could be argued that there is excess population, but the current population is able to temporarily ward off the Malthusian constraint at the cost of future populations. Even if this were the case, however, I would prefer to frame that argument in terms of the nature of the technology than in terms of “excess population”. A state of excess population is the norm, not a particular result of agriculture or any other technology of the day.