The rapid dispersal of archaic human populations across the globe was the result of developing human nature, where morality is at play among social relationships, a new study revealed. More importantly, the study said that the betrayal of trust within a social group, whatever the size, incited early humans to take risks for survival.

Around 100,000 years ago, the motivation and speed of how early humans spread around the world shifted significantly, explained Dr. Penny Spikins of the University of York's Archeology Department.

Before the shift, the movement of these early humans was slow and hugely influenced by events in their environments, which were caused by changes in the Earth's ecology or increases in population. Afterwards, the speed with which human populations spread became remarkable. Humans also trotted across environmental barriers, experts said.

Spikins, the lead author of the new study featured in the journal Open Quaternary, however believes the shift is related to the change in human emotional relationships. She explained that neither changes in the Earth's ecology nor increases in population offer a sufficient explanation for patterns of human dispersal into new areas around 100,000 years ago.

As commitments to other human beings became more vital in survival, and as the concept of punishment to humans who cheat was beginning to emerge, the "dark side" of human nature also developed, Spikins said.

Moral disputes which were caused by broken trust and the sense of betrayal became more frequent among early humans, and these motivated them to get away from their enemies while taking any risk to do so.

Populations which were held together by emotional bonds during crisis had darker and more heartfelt reactions to betrayal, Spikins said, all of which humans today still experience. The larger the social network, the easier it was for early humans to form alliances with whom to create new colonies.

Pre-historic humans who had more efficient hunting tools were armed against their enemies. Anyone who bore a grudge was dangerous, and it was the emotions which fueled the force of repulsion from previously occupied areas. This is something that cannot be seen in other animals.

"While we view the global dispersal of our species as a symbol of our success, part of the motivations for such movements reflect a darker, though no less 'collaborative', side to human nature," said Spikins.

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