100,000 Years of Dramatic Population Changes

Since the invention of agriculture 11,000 years ago, human 
population has trended up—but the boom may be drawing to an end. Birthrates are falling around the world; by the end of the century the number of people on the planet may top out and, in an unprecedented reversal, start to decline. Good news, right? The answer is not so simple. Growing populations are associated with progress; shrinkage has often correlated with cultural decline. One stark example comes from Tasmania, an island off southeast Australia. Nearly the size of Ireland, it was colonized 34,000 years ago by people with sophisticated toolmaking skills who came across a land bridge from Australia. By the 18th century, Tasmanians used simple technology, hunting with rocks and crude clubs. In 2004 anthropologist Joseph Henrich used a mathematical model of cultural evolution to tackle this mystery [pdf]. He concluded that the island’s population, about 4,000 in the 18th century, at some point fell below the level necessary for complex skills to be passed from generation to generation. Scientists increasingly think population size and density have had a big impact on human development at certain pivotal points. That continues in the modern world, as young people disproportionately produce innovation, generate economic growth, and finance social support networks for the elderly.