One approach to the relative scale of prehistoric communities is to calculate the amount of effort it takes to build their monuments …
Building teams of five to ten workers could have constructed the smaller tombs, which is not an unreasonable input for even a small-scale clan. In some tombs there are several burial chambers, which might indicate that more than one clan-group — tribal relatives, perhaps — came together to create the earliest and longest-surviving monuments in Britain; but monument building was becoming competitive. The works of man began to increase in scale as the population grew. British society was changing and becoming more complex and more stratified. Some people wanted to lead the tribe and to display their status for all to see.
By the way, Malcolm believes that — on the basis of a similar estimate — the population of the Boyne valley today is roughly the same as that required to support the construction of Newgrange.