Historical Overview

How has human population size changed over time?

The human population, like populations of other organisms, tends to increase. The rate of that increase has changed dramatically over time. For most of human existence, the population grew slowly because life was harsh. Food was hard to find. Predators and diseases were common and life-threatening. These limiting factors kept human death rates very high. Until fairly recently, only half the children in the world survived to adulthood. Because death rates were so high, families had many children, just to make sure that some would survive.

Exponential Human Population Growth As civilization advanced, life became easier, and the human population began to grow more rapidly. That trend continued through the Industrial Revolution in the 1800s. Food supplies became more reliable, and essential goods could be shipped around the globe. Several factors, including improved nutrition, sanitation, medicine, and healthcare, dramatically reduced death rates. Yet, birthrates in most parts of the world remained high. The combination of lower death rates and high birthrates led to exponential growth, as shown in Figure 5–11.

The Predictions of Malthus As you've learned, this kind of exponential growth cannot continue forever. Two centuries ago, this problem troubled English economist Thomas Malthus. Malthus suggested that only war, famine, and disease could limit human population growth. Can you see what Malthus was suggesting? He thought that human populations would be regulated by competition (war), limited resources (famine), parasitism (disease), and other density-dependent factors. Malthus's work was vitally important to the thinking of Charles Darwin.