ANOTHER LARGE and daunting twenty-first century problem involves equal access to food. Today, fertility rates in third-world countries have decreased sharply even as global per capita calorie consumption has risen, the twin phenomena casting doubt on predictions of swelling populations outstripping the globe's food supply. Such predictions were routinely generated by that alarming increase in the number of people occupying planet Earth between 1900 and 1990, which was the equal of four times the sum of all previous increases in the whole of human history. But although we are now 6 billion, with predictions of an increase to 9 billion by 2050, it would seem that agricultural advances have probably resolved concerns about food quantity. There are enough calories for everyone. Yet fully three-quarters of the world's population derive their calories from a diet that is low in high-quality protein compared to the other quarter who consume too much of it in diets that are definitely not tailored for a small planet. And the problem is, as Tony McMichael points out, that if food consumption was somehow made equal in terms of quality, the globe could not currently support our 6 billion; to do so would require two extra planet earths given our current technologies, and to support 10 billion would require four extra earths.