London: Betrayals of trust resulting from moral disputes forced early humans to cross major geographical barriers, including deltas such as the Indus and the Ganges, and spread across the world about 100,000 years ago, a new study has found.
Penny Spikins from the University of York in the UK said that the speed and character of human dispersals changed significantly around 100,000 years ago.
Before that movement of archaic humans were slow and largely governed by environmental events due to population increases or ecological changes.
Afterwards populations spread with remarkable speed and across major environmental barriers. Spikins relates this change to changes in human emotional relationships.
Researchers said that neither population increase nor ecological changes provide an adequate explanation for patterns of human movement into new regions which began around 100,000 years ago.
They suggest that as commitments to others became more essential to survival, and human groups ever more motivated to identify and punish those who cheat, the 'dark' side of human nature also developed.
Moral disputes motivated by broken trust and a sense of betrayal became more frequent and motivated early humans to put distance between them and their rivals.
Larger social networks made it easier to find distant allies with whom to start new colonies, and more efficient hunting technology meant that anyone with a grudge was a danger but it was human emotions which provided the force of repulsion from existing occupied areas which we do not see in other animals.
Early species of hominin were limited in distribution to specific environments such as grasslands and open woodland.
The expansion of Homo erectus out of Africa into Asia around 1.6 million years ago appears to have been caused by the need to find more large scale grasslands.
By contrast, Neanderthals occupied cold and arid parts of Europe. All archaic species adapted slowly to new opportunities for settlement and were often deterred by environmental and climatic barriers.
After 100,000 years ago, dispersal into distant, risky and inhospitable areas became relatively more common compared with movements into already occupied regions.
Humans moved into cold regions of Northern Europe, crossed significant deltas such as the Indus and the Ganges, deserts, tundra and jungle environment and even made significant sea crossings to reach Australia and the Pacific islands.
Spikins said that betrayals of trust resulting from moral disputes were a significant reason for such risky dispersals into apparently unwelcoming environments with a desire to avoid physical harm from disgruntled former friends and allies being a key motivation.
The study was published in the journal Open Quaternary.