Complex sentence: As early hunter-gatherer societies involved concentrations in small groups and widely scattered (as in the case of the Alaskan Eskimo population referred to above) diseases infecting these early human societies must therefore have originated from an outside source.
Split into simpler sentences: As early hunter-gatherer societies involved concentrations in small groups and widely scattered (as in the case of the Alaskan Eskimo population referred to above). Diseases infecting early human societies must therefore have originated from an outside source.