It has generally been accepted that by the time the last glacial ended around 12-13,000 years ago the world-wide human population was between 4 – 6 milllion people and as agriculture and a settled life style began population exploded reaching about 60-70 million by about 6,ooo years ago (4,000BCE).
Last year Chinese researchers suggested from genetic studies that the population probably began expanding some time before the neolithic probably after the Last Glacial Maximum (around 25,000 years ago) but before the establishment of the full inter-glacial conditions in the Holocene neolithic. This appears logical since even during the glacial period the conditions around the equator and tropics would have been relatively mild and fertile.
The authors suggest that the milder climate after the Last Glacial Maximum may have offered a more amiable environment and may have been an important factor in prehistoric human expansions. The increase in population size was probably one of the driving forces that led to the introduction of agriculture, turning it from a supplementary food source to the primary one.
But a new paper now suggests that population expansions probably began much earlier and even before herding and agriculture were established already while humans were predominantly hunter-gatherers. This would have been in the paleolithic and perhaps 60,000 – 80,000 years ago.
Human genetic data reveal contrasting demographic patterns between sedentary and nomadic populations that predate the emergence of farming, C. Aiméa, G. Laval, E. Patin, P. Verdu, L. Ségurel, R. Chaix, T. Hegay, l. Quintana-Murci, E. Heyer and F. Austerlitz, Mol Biol Evol (2013) doi: 10.1093/molbev/mst156
Now, researchers Aiméa, et al., have challenged this assumption using a large set of populations from diverse geographical regions (20 different genomic regions and mitochondrial DNA of individuals from 66 African and Eurasian populations), and compared their genetic results with archaeological findings. The dispersal and expansion of Neolithic culture from the Middle East has recently been associated with the distribution of human genetic markers.
They conclude that the first significant expansion of human populations appears to be much older than the emergence of farming and herding, dating back to the Paleolithic (60,000-80,000 years ago) rather than Neolithic age. Therefore, hunter-gatherer populations were able to thrive with cultural and social advances that allowed for the expansion. The authors also speculate that this Paleolithic human population expansion may be linked to the emergence of newer, more advanced hunting technologies or a rapid environmental change to dryer climates.
Finally, they also suggest that strong Paleolithic expansions may have favored the emergence of sedentary farming in some populations during the Neolithic. Indeed, the authors also demonstrate that the populations who adopted a sedentary farming lifestyle during the Neolithic had previously experienced the strongest Paleolithic expansions. Conversely, contemporary nomadic herder populations in Eurasia experienced moderate Paleolithic expansions, and no expansions were detected for nomadic hunter-gatherers in Africa. “Human populations could have started to increase in Paleolithic times, and strong Paleolithic expansions in some populations may have ultimately favored their shift toward agriculture during the Neolithic,” said Aiméa.
A semi-nomadic herding life-style with temporary settlements could well have allowed sufficient resources for population expansions and also have been consistent with the geographical expansions of humans.