Free Lone Survivors by Chris Stringer

There are many clues to this, including chemical signs of freshwater deposition and dark sapropels in deep-sea cores off the coast of Libya, both of which indicate powerful river sediments during the last interglacial. A similar signal was detected from plant-derived chemicals in dust deposits off the West African coast; analysis shows that the level of water-dependent plants (such as trees rather than grasses) peaked around 115,000 years ago, with a briefer second peak from about 50,000 years.
    In addition, as revealed in radar images from satellites, huge river channels now lie buried beneath desert sands, some of which are five kilometers wide and run for eight hundred kilometers. As the earth scientist Nick Drake and his colleagues showed, around 120,000 years ago the desert was covered by an interconnecting network of rivers and lakes, forming humid corridors that stretched from massive southern lakes such as Fazzan and Chad all the way to the Mediterranean. These corridors allowed typical African fauna and flora to flourish for at least 20,000 years, and as plant resources and game proliferated, so did the humans who lived off them. For the last hundred years, travelers and archaeologists have collected Middle Paleolithic tools from the surface of the Sahara, often well away from any modern oases, and we now know that many of those accumulations date from the green Sahara over 100,000 years ago.
    The tools include triangular stone points with a tang or shoulder, which was presumably used to mount them as projectiles on a wooden handle. These iconic artifacts characterize the Aterian industry, first recognized at the Algerian site of Bir el-Ater; this industry was made by a very robust and large-toothed variety of early Homo sapiens , comparable to the people we know from Herto in Ethiopia. It seems very likely that the increased humidity of many parts of Africa at this time led to population growth and an important sharing of ideas across Africa, as formerly isolated regions became connected by habitable corridors. Cultures that used shell beads and red ocher pigment to signal to each other seem to have spread across the whole known range of early modern humans at that time, from South Africa to Morocco and even into adjoining western Asia, at Skhul and Qafzeh. In Israel, elevated rainfalls produced the huge Lake Samra, which extended far beyond the now shrunken Dead Sea basin, about 75,000 to 135,000 years ago.
    But as the beginnings of the last Ice Age began to grip, these balmy interglacial conditions were not to last in Africa. We can trace the effect of this climatic downturn on the peoples of southern Africa from about 75,000 years ago through two important and innovative stone tool industries: those at Still Bay and Howiesons Poort. As well as sophisticated stone artifacts (heat-treated to improve flaking qualities in the case of the Still Bay), both possessed beads made of seashells or ostrich eggshells, and both used red ocher symbolically. The Still Bay industry is known from only a handful of spots in southern Africa, while the Howiesons Poort was much more widespread, with at least thirty sites ranging from the best-known locations on the southern coasts at places like Klasies River Mouth Caves, to the edges of the Namib Desert and the mountains of Lesotho. While it was thought that the Still Bay preceded the Howiesons Poort, they both lay well beyond the limit of effective radiocarbon dating, so methods like uranium series and ESR had been employed to place them in relation to each other, but with a poor fix on their respective durations.
    The breakthrough came in 2008 when a team of dating specialists including Zenobia Jacobs and Bert Roberts combined with archaeologists such as Hilary Deacon and Lyn Wadley to apply the latest luminescence dating techniques to single grains of quartz from the sites, using the same laboratory procedures throughout. Fifty-four samples were obtained from widely dispersed sites