Mosaic Evolution and Parsimony

Sat, 11 Feb 1995 12:58:19 CST

R. Holloway asks whether I have heard of mosaic evolution; J.
Ottevanger, in a related vein, calls it "glib" to assume that the
appearance of basic hominid adaptations--bipedalism, canine reduction,
and the precision grip--were "simultaneous." In response I would say
that yes, I am somehat familiar with the concept of mosaic evolution;
and that "simultaneous" is not how I put it. What I wrote, I believe,
was that these three important features "seem" to have "coincided." Even
that was a bit strong. What I mean is that all three appear, by the
evidence, to have great antiquity in hominid evolution, and cannot at
this time be chronologically disarticulated. It appears to me
unparsimonious to assume mosaic evolution until the evidence makes you.
After all, if the three traits arose as a kind of package, you don't
need separate explanations; and one explanation for three traits would
be neater than three explanations. What if, furthermore, the one
explanation you came up with also seemed to help account for subsequent
brain expansion; and what if, finally, the one explanation was perfectly
consistent with volumes of ethnographic and ethological data? That one
explanation, of course, is increasing reliance on the making and using
of tools. R. Holloway does not like tool-use as an explanation for cani
ne reduction; but the alternatives appear little better, and sacrifice
the parsimony. M. Hill instantiates Rindos' point--correctly, I think;
but as I already responded to that I will not do so again here. Let me
conclude by stressing that (1) all known human societies rely heavily
on the making and using of tools for their survival, while no other
known species does so; (2) many species manage social relationships well
enough to live in societies at least as large as foraging bands without
need of human-like intelligence, so the social-intelligence hypothesis f
ails at the outset (and lacks the tremendous parsimony of the technology
hypothesis);and (3) rudimentary tool-use, more developed than in any
species save our own, occurs precisely where, according to the
technology hypothesis, it should: among our nearest living relatives,
the chimpanzees. --Bob Graber