Germs, Genes, & Civilization: How Epidemics Shaped Who We Are Today

11. Emerging diseases and the future

Pandemics and demographic collapse

Today our planet holds approximately 6 billion humans and 5 × 10³⁰ (5 million trillion trillion) bacteria. We are outnumbered by nearly 10²¹ (1 sextillion) to 1. At the moment, we are catching up. But will this trend last? The human population does not climb smoothly. Periods of growth are followed by population crashes. When will the next population implosion happen? How?

The earliest major population collapse for which we have reliable records occurred in the Roman Empire as a combined result of the unidentified pestilences of 165 A.D. and 251 A.D. The plague of Justinian, which began in 542, with secondary epidemics until 750, was another period of major population decline ...