© Eric R. Pianka
Until the advent of agriculture about 10,000 years ago, humans were hunter gatherers -- many fewer of us existed. Food supplies lead population -- populations increase to the level that foods will allow. Agriculture has been called one of the worst mistakes humans ever made because it allowed us to increase in population density, ultimately leading to the present day overpopulation crisis. We could never have reached 6.8+ billion without fossil fuels. Basically, humans exploited these one-time fossil energy reserves to demolish many of Earth's natural ecosystems and turn them into arable land and crops to feed increasing numbers of people. We replaced the tall grass prairies of North America with fields of corn and wheat and turned bison herds into cattle, ultimately into masses of humanity. Without agriculture, we could never have built cities, let alone our civilization and human knowledge. However, in many ways cities are giant but fragile and unsustainable feed lots for unnaturally dense aggregations of humans.
The deep black topsoils of the prairies made America a 'bread basket' for the world, allowing us to export grains to less fortunate peoples in other parts of the world without access to such amenable climates and rich soils. Sustained agriculture depletes the nutrient pools of soils -- in order to maintain production, soils must be fertilized with nitrogen and phosphorus and other minerals. Animal wastes such as bat and bird guano were used as fertilizers until they began to be depleted. Then, just as such natural fertilizers were running out, the Haber-Bosch process was discovered, which allowed natural gas to be burned to turn inert atmospheric nitrogen into ammonia fertilizer. Without this technological breakthrough, human populations would have become limited by food supplies long ago and at much lower population densities. The advent of these inexpensive fertilizers has encouraged overuse resulting in massive nitrogen pollution. Eventually, we will exhaust finite natural gas supplies. This technology has lured us out on to thin ice, and we now must face population overshoot (Catton 1982). Sadly, our enormous population, now well above the level Earth can support, must soon crash, accompanied by famines and massive human misery.
Catton, W. R. 1982. Overshoot. The Ecological Basis of Revolutionary Change. University of Illinois Press. Excerpt
Diamond: The Worst Mistake in the History of the Human Race