It has been said in the movies that life can't be contained. So why limit expansions of populations only to the advent of agriculture? Think people expanded across vast territories only after agriculture set people in search of land where food could be grown and homes built? In a new study scientists found that expansions likely predated the emergence of agriculture and herding.
Populations could have started to expand in Paleolithic times, says a new study. The former assumption long touted in the mainstream media emphasized that human populations expanded long before the new stone age, known as the Neolithic times which refers to what happened after the discovery of agriculture. In fact, people have been expanding in search of new land and more food for around 60,000 to 80,000 years, says a new study that looks at autosomal DNA and tracks how genes spread across the globe in the distant past.
The new genetic study pushes back timeline for first significant human population expansion, says a new study published this week on September 24, 2013 in the advance access edition of the journal Molecular Biology and Evolution (Oxford University Press). Using new genetic tools, the authors 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 (10,000 years ago).
They also suggest that strong Paleolithic expansions may have favored the emergence of sedentary farming in some populations during the Neolithic, says a September 24, 2013 news release, "Genetic study pushes back timeline for first significant human population expansion." Check out the abstract of the latest study, "Human genetic data reveal contrasting demographic patterns between sedentary and nomadic populations that predate the emergence of farming."
About 10,000 years ago, the Neolithic age ushered in one of the most dramatic periods of human cultural and technological transition, where independently, different world populations developed the domestication of plants and animals
The hunter-gatherers gave rise to herders and farmers. Changes to a more sedentary lifestyle and larger settlements are widely thought to have contributed to a worldwide human population explosion, from an estimated 4-6 million people to 60-70 million by 4,000 B.C.
Now, researchers Aimé, 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," says Aimé in the September 24, 2013 news release, "Genetic study pushes back timeline for first significant human population expansion. The scientists used genetic data rather than just archaeology's artifacts to dig out the past.
Demographic changes are known to leave footprints on genetic polymorphism
Together with the increased availability of large polymorphism datasets, coalescent-based methods allow inferring the past demography of populations from their present-day patterns of genetic diversity, says the abstract of this new study. Here, the researchers analyzed both nuclear (20 non-coding regions) and mitochondrial (HVS-I) re-sequencing data to infer the demographic history of 66 African and Eurasian human populations presenting contrasting life-styles (nomadic hunter-gatherers, nomadic herders and sedentary farmers).
This allowed the researchers to investigate the relationship between life-style and demography, and to address the long-standing debate about the chronology of demographic expansions and the Neolithic transition. In Africa, the researchers inferred expansion events for farmers.
Researchers studied autosomal DNA data
One variable the scientists examined focused on the constant population sizes or contraction events for hunter-gatherers. In Eurasia, the researchers inferred higher expansion rates for farmers than herders with HVS-I data, except in Central Asia and Korea. Although isolation and admixture processes could have impacted our demographic inferences, these processes alone seem unlikely to explain the contrasted demographic histories inferred in populations with different life-styles.
The small expansion rates or constant population sizes inferred for herders and hunter-gatherers may thus result from constraints linked to nomadism. However, autosomal data revealed contraction events for two sedentary populations in Eurasia, which may be caused by founder effects.
Finally, the inferred expansions likely predated the emergence of agriculture and herding. This suggests that human populations could have started to expand in Paleolithic times, and that strong Paleolithic expansions in some populations may have ultimately favored their shift towards agriculture during the Neolithic.