late pleistocene population interaction in western europe

obustus up to modern man of today. If all hominid types and their variations, regardless
of time and space, are taken into consideration, their arrangement in a continuous
evolutionary line, leading from the most primitive state to the most advanced, does not
meet with any difficulty. Neither any gaps nor deviations are recognizable. This
statement holds good for the entire skeleton, in particular for skull and dentition, and
concerns this part not only as a whole, but also their minor structures and special patterns
(Weidenreich 1947:189; original emphasis).
Importantly, Weidenreich agreed with McCown and Keith (1939) that the fossil
sample from the Levant is intermediate in form between Neandertals and early modern
humans. The mechanism ensuring continuity is described:
All this points to an already world-wide distribution of early phases which transmuted
into more advanced types by vertical differentiation, while they split into geographical
groups by horizontal differentiation. Both processes may have been accelerated or
retarded at certain times and in certain places (…) One can speculate about their causes.
They might have been due to general environmental conditions, yet the state of the
population as regards its density or scarcity, migration, interbreeding and extermination
certainly played a decisive role (Weidenreich 1947:202).
Although gene flow is not particularly emphasized in the text, except for
occasional references to “crossing” and “interbreeding,” a figure on p. 201 of the same
paper is explicit about its role in the evolution of modern humans. Clearly, Weidenreich’s
reticulate model includes most of the ingredients and concepts of what will later become
known as the “Multiregional” model (Wolpoff and Caspari 1996).
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