Elsewhere I have summarized a large body of evidence that ties the numerical size and growth of the population of Homo sapiens to a wide range of human-caused, negative effects on nature and the social life of people. Simply put, the growing number of human beings, especially by expanding the amount of land devoted to urban areas, is placing ever-greater demands and stress on the biosphere. In Chapter Two, I extend this body of evidence with additional studies of specific ways in which the biosphere and human societies have been injured by the increasing number of people on Earth. These studies are in line with recently published research that found the overall ecological footprint of the human species becomes larger as the number of human beings grows. For example, a study covering 188 jurisdictions (nations and territories) during the years 1961 through 2016 concluded that the ecological footprint of the jurisdictions was made greater by additions to human-population density in the jurisdictions.

2.1 COVID-19

I start my review with a subject on which I briefly touched earlier, viz., the COVID-19 pandemic.5 Recent research has found that human-population density is positively related to the scale and severity of the COVID-19 outbreak — as population density went up, the COVID-19 pandemic worsened.

• 1. The basic reproduction number (R0) for COVID-19, that is, the number of people in a susceptible population who were infected with COVID-19 by a single infected person, was the dependent variable in a study of 274 cities across the globe (but outside China) that had a population of not less than 500,000. With population size held constant, R0 increased as population density rose. Population density, in other words, added to the number of infected people independently of population size (as well as, inter alia, the level of air pollution).6

• 2. Similarly, in a study of more than 150 nations worldwide, both higher population density and a larger proportion of the population that resided in an urban area were each found to raise the number of current active cases of COVID-19, with current active cases defined as the total number of cases after accounting for persons with COVID-19 who died or recovered from the disease.