In 1999 my South African colleague Peter Nilssen and I decided to investigate some caves he had spotted at a place called Pinnacle Point, a promontory near the town of Mossel Bay that juts into the Indian Ocean. I had to find a shelter close enough to the ancient coastline to provide easy access to shellfish and elevated enough that its archaeological deposits would not have been washed away between 130,000 and 125,000 years ago, a period of transition when the climate warmed and sea levels surged. My search within that coastal area was not random. DE VYNCK Center for Coastal Paleosciences, Nelson Mandela University ( image) PP13B and other caves carved into the sheer cliff face of a promontory called Pinnacle Point meet those requirements and have yielded a plethora of remains dating to this critical juncture in human prehistory.Д¬redit: Don Foley ( map), Lucy Reading-Ikkanda ( globe) В J. The southern coast would have been a particularly plentiful oasis, thanks to three rich resources-the edible fynbos plants that grow only here the dense shellfish beds nurtured by the Agulhas current and the Benguela upwelling of nutrient-rich cold water from the sea bottom and the populations of large mammals living on the exposed plain.ДЇinding archaeological sites dating to glacial stage 6 required searching for shelters that were close enough to the sea to allow relatively easy access to shellfish yet elevated enough that their ancient remains would not have washed away when the sea level rose 123,000 years ago. Only a few regions could have supported our species, namely, those with grassland or Mediterranean scrub vegetation. So, in 1991, I decided I would go there and look for sites with remains dating to glacial stage 6.Д«etween 195,000 and 123,000 years ago, the planet was locked in an ice age known as Marine Isotope Stage 6, rendering much of the African continent cool and arid-unsuitable for the plants and animals that Homo sapiens ate. The southern coast of Africa, rich in shellfish and edible plants year-round, seemed to me as if it would have been a particularly good refuge in tough times. Paleoanthropologists argue vociferously over which of these areas was the ideal spot. Where, I wondered, did our ancestors manage to survive during the climate catastrophe? Only a handful of regions could have had the natural resources to support hunter-gatherers. Humans today exhibit very low genetic diversity relative to many other species with much smaller population sizes and geographic ranges-a phenomenon best explained by the occurrence of a population crash in early H. But my interests began to shift when I learned of the population bottleneck that geneticists had started talking about in the early 1990s. I began my career as an archaeologist working in East Africa and studying the origin of modern humans. Given the narrow genetic diversity of modern humans, it seems likely that the main progenitor population was a single group, perhaps one ethnolinguistic group, that lived in one region and then spread outward, mixing with other populations as it moved. Estimates of the timing of the bottleneck tend to be at around 150,000 years ago. Geneticists debate how small this population was, but it could have been as few as several hundred individuals. While the planet was in the grip of this icy regime, the number of people plummeted, and only a subset contributed to the surviving population. Much of the landmass would have been uninhabitable. The planet entered a long glacial stage known as Marine Isotope Stage 6 (MIS6) that lasted until roughly 123,000 years ago.ДЄ detailed record of AfricaвЂ™s environmental conditions during glacial stage 6 does not exist, but based on more recent, better-known glacial stages, climatologists surmise that it was almost certainly cool and arid and that its deserts were probably significantly expanded relative to their modern extents. But around 195,000 years ago, conditions began to deteriorate. Back then the climate was mild and food was plentiful life was good.

Although scientists lack a precise time line for the origin and near extinction of our species, we can surmise from the fossil record that our forebears arose throughout Africa shortly before 195,000 years ago.

Yet studies of the DNA of modern-day people indicate that, once upon a time, our ancestors did in fact undergo a dramatic population decline. With the global population of humans well beyond seven billion, it is difficult to imagine that Homo sapiens was once an endangered species.

Weapons of a new millenia