After millennia of modest growth, the human population started growing exponentially in the last few centuries. The human habitat has expanded, with population density primarily a function of NPP, distance to coasts and rivers, and altitude. Population growth in Europe underwent the so-called demographic transition as a consequence of changes in fertility and mortality. This was caused by several developments within the broader transformation into Modernity. It was and is repeated at a faster rate in regions outside Europe. One perspective on human behaviour (and reproduction) stems from evolutionary biology, with views on competition--cooperation, selfishness--altruism and niche construction. Complementary views emphasize the role of environmental and sociocultural factors, describing long-term evolution in terms of regimes and syndromes. Growth of the human population has large inertia, but there is still a wide margin of uncertainty in the estimates of quantity and quality of humans by the end of the twenty-first century. Some uncertainty, for instance about abortion, euthanasia and migration, can be understood in terms of divergent worldviews.

The Introduction to Earthopolis: A Biography of Our Urban Planet outlines large themes in the 6,000-year story of how cities gave humans the power to dominate Earth. Our Urban Planet is at once a plural and a singular phenomenon. Its diversity reflects the many birthplaces and birthdates of cities on six continents over six millennia, yet it has become a connected city-enabled habitat of a single species on a single planet. Cities – compact built spaces that rely on many other, dispersed ones – allowed us to harvest enough energy from the Sun and Earth to create the political communities, institutions, wealth, and ideas we needed to act on a global scale, to build an Earth-encrusting habitat, to impact all other parts of our planet’s biosphere, and to face the consequences. The life of Earthopolis exists in space and time. As our urban harvests of natural energy transformed throughout global urban history, from river valleys to the world ocean, and then to hydrocarbon, the geographic extent of our Urban Planet’s four defining realms – of human action, habitat, impact, and consequence – expanded and retreated across Earth. Now our Urban Planet puts us in perilous command of our host planet’s entire halo of life.