Outward pressure

Easter Island is a triangular speck in the Pacific Ocean, over a thousand miles from the nearest inhabited land. When it was 'discovered' by the Dutchman Jacob Roggeveen, on Easter Sunday 1722, it already had people living on it.

Humans had only been on Easter Island since about AD 1000. Nevertheless, that they had reached this remote spot points to humanity's strong centrifugal tendency. Humans were already in Australia a few thousand years after our emergence as a species, and that journey would have required a sea crossing at some point.

This shows that people do not naturally live together at high densities. They are driven, to some extent, to get away from each other. This outward pressure has several aspects:

1. For a given technology and way of life, a particular land area will support a limited number of people. As population increases, humans find it easier to move to empty land than to develop ways of supporting more people from the same territory.
2. Living together causes friction and conflict. Some people may bully others or may impose themselves on others in an effort to keep order. At least part of the population finds it preferable to move away, rather than stay and have its freedom curtailed.
3. While many humans are happy to drift along with what they know, others have a high degree of 'natural curiosity' that makes them want to explore beyond the known, both geographically and in other ways.

It is now fairly clear, based on genetic data, that humans arose in Africa recently, and spread out from there. Modern humans are therefore all quite closely related.

Nevertheless, I disagree in detail with current reconstructions of the peopling of the world (link requires Google Earth; a Google Maps version is here). According to the view presented in the preceding link, while people reached Australia about 40,000 BC, they did not reach North Africa until 20,000 BC, even though they had evolved on the African continent. Furthermore, while people had got half-way down the African coast by 40,000 BC, they supposedly did not reach the southern tip of Africa until 25,000 BC, even though they were in China and Spain by 40,000 BC and in Britain only a couple of thousand years later. Such a pattern makes little sense and rather shows the limitations of the gene-mapping methodology on which this reconstruction is based.

I suggest that, after emerging in central east Africa, the human species spread to and throughout every continent within a few thousand years, say around 40,000 BC. Only the peopling of oceanic archipelagoes that are not connected to the mainland by chains of intervisible islands did not occur until much later, say from about 5000 BC.

(Although mainstream opinion holds that humans did not move into the Americas until after about 15,000 BC, some archaeologists do place the entry into the Americas around 40,000 BC, on the basis of sites that remain controversial.)

I am still researching this issue...