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During the five great biotic extinctions, huge numbers of species were lost. Over evolutionary time, biodiversity was restored and sometimes exceeded previous levels. This environment might well be described as a pulsing system that was affected by catastrophic natural events (e.g., the impact of a large object from outer space with Earth). The sixth great extinction, now underway, differs from the first five because the major influence is human activities. Will the resulting ecological changes also have adverse effects upon human society? Global warming and other types of climate change, the coming decline in the availability of petroleum, acidification of the oceans, continued growth of the human population in both numbers and expectations, and ecological overshoot will surely have deleterious effects. Unanswered questions remain: (1) will humans replace their unsustainable lifestyle with sustainable use of the planet? and (2) if so, will social evolution be sufficiently rapid to be effective? As a species, humans are embedded in a huge, complex, multivariate system that will probably endure even if the human species becomes extinct.