The principle obstacle to human dominion over the rain forests is still the rich variety of parasites lying in wait for intruders. - William Hardy McNeill

Details of early domestications remain unclear. One must assume a process of mutual accommodation between humanity and various domesticable species. This involved rapid and sometimes far-reaching change in the biological character of domesticated plants and animals as a result of both accidental and deliberate selection for particular traits. Conversely, one can assume that a radical, if rarely deliberate, selection among human beings occurred as well. Individuals who refused to submit to laborious routines of farming, for instance, must often have failed to survive, and those who could not or would not save seed for next year's planting, and instead ate all they had, were quickly eliminated from communities that become dependent upon annual crops.

The single most important stimulus to my thought came by chance when I took a course from Robert Redfield entitled "Folk Society." …His approach was to set up antithetical ideal types, expecting to locate any actual human community somewhere along the spectrum of opposites his fieldwork had suggested to him. ...But in 1936 his typology had no time dimension. I was so strongly attracted to his scheme that it is scarcely an exaggeration to describe my subsequent intellectual effort as an attempt to explore the missing time dimension of social change as Redfield envisaged it, not in Yucatan but around the whole earth and across recorded time.

The laws of nature, as analyzed mathematically and descriptively by Ptolemy and Galen, bore an interesting, and perhaps not entirely accidental similarity to the law of nations and of nature, as discerned by a long succession of Roman jurists. ...The concept of an objective law applicable to human affairs, yet operating in accord with Nature and Reason and apart both from divine revelation and from human whim or passion, was peculiar to Rome and societies descended from Rome.