Nature builds a number of controls into the system, so that overpopulation will not occur.
Limited food supply
We have found ways around this problem, thanks to the use of fossil fuels for fertilizer, pesticides, herbicides, irrigation, cultivation, and fast transport to market.
If humans live in close proximity to each other without adequate sanitary precautions, infectious diseases become a problem. In today’s world, these are not much of a problem, because we have built water and sewer systems, and have developed antibiotics. Doing these things required external energy sources, generally oil and other fossil fuels.
Craig Dilworth in “Too Smart for Our Own Good” says that there are instinctual behaviors that would normally act to prevent overpopulation. One of these is territoriality. Primates and most mammals are what are called K-selected species.
In K-selected species, territoriality tends to hold down population size by restraining the number of breeding pairs. We have all seen territoriality, if we have male cats or dogs. They mark out their territories, and defend them.
The territories chosen by instinct by K-selected species are large enough to ensure that populations do not grow to such a size that they undermine their own resource base. Thus, if territoriality is working properly, there is no problem with tragedy of the commons (excessive use of shared resources), because the territory selected by the male for his family group is large enough to feed the family, with much available food left over.
Humans have managed to overcome territoriality to a significant extent. One mechanism is language, since it allows humans to communicate with one another. Another is trade. If an outsider is of some value to us because of goods we gain through trade, then an individual is less likely to kill the outsider when he comes into contact with him. …. The availability of sufficient resources, as has mostly been the case since World War II thanks to fossil fuels, may also act to reduce territoriality.
Other K-selected population control factors
- Too high population tends to cause stress and leads to violence against neighboring groups. The winner gets more territory; the losers typically are killed.
- Infants may be killed, to keep the population in line with resources.
- Learned behaviors or instincts may limit when mating takes place.
- High population will tend to attract predators (germs, in the case of humans)
- If population is too high, hierarchical behavior (another instinctual mechanism) may appear or increase. Because individuals who do not need resources get a disproportionate share of the total, there is less for those at the bottom of the hierarchy, helping to reduce population size more quickly than if resources are shared equally. Those at the top are spared.