All living things produce young sufficiently to maintain the numbers of their species; any species that fails to do this will obviously become extinct. Living things must produce surplus offspring, more than just sufficient to replace themselves because not all of their offspring will survive — many will succumb to disease, predation, accident or lack of resources such as food or water.

Different strategies have developed for different living things that ensure that sufficient of their offspring survive to reproduce and maintain the population necessary for the species to continue. Many plants, insects, and fish produce literally millions of offspring during their lives, giving them no care or support and relying on sheer numbers, while other living things produce small numbers of offspring and nurture them carefully. Human beings fall into the latter group.

If the environment that a population of living things is part of changes so that the restraints on the survival of offspring don’t occur, then the surplus offspring will survive and the population will grow. This may occur if a species that predates on them has its population reduced by disease, if an alternative prey species for the predator species becomes available, if a species that competes for a resource has its population reduced greatly by disease or predation, or many other reasons.

Generally, any species must always produce an excess of offspring, an excess that has the potential to increase its population if not restrained, but that is usually restrained by the nature of its environment.

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 Why our population grows

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