mosaic evolution

Alex Duncan (
27 Nov 1995 00:52:23 GMT

In article <> Elaine Morgan, writes:

>No, but what it does require is a further proliferation of time scales
>for all the different types of anomaly in human physiology. We are asked
>to believe, wwithout any evidence one way or the other, that all these
>unique attributes emerged serially. Bipedalism first, for a reason that
>is still up for grabs, nakedness later at an unspecified time for an
>unspecified reason, laryngeal descent at some other time for some even
>more mysterious reason, and now the tears thing latest of all - it sounds
>as if you are post-dating this to the Industrial Revolution.
>There is no evidence that they didn't happen at the same time and for the
>same reason, which would be far more parsimonious. The only reason for
>rejecting this supposition is that the one thing that may logically
>link them is water,

If we carry your argument to its logical conclusion, we must "postdict"
that the earliest hominids were EXACTLY like humans, because all of the
features that make us unique would have had to have evolved at the same
time, in order to be parsimonious. In other words, if we find a modern
Homo sapiens in 4 Myr old sediments, I'll write the next book supporting

One thing that has become very obvious from study of the fossil record is
that evolution proceeds in a mosaic fashion. This is true for most
lineages that I'm aware of (w/ the exceptions being examples of long-term
stasis, e.g., horseshoe crabs). The evolution of mammals from primitive
amniotes is an excellent example of the phenomenon. The evolution of
humans from ape-like hominoids is another. In fact, the fossil record
speaks to us very clearly about this issue in regard to hominid
evolution, and what it says is that hominids evolved in mosaic fashion,
through the gradual accumulation of human-like traits.

In other words, using the fossil record as our guide, there is no reason
to assume that all human-like features appeared at once, and in fact
there are very good reasons to assume otherwise. Your insistence on a
"one-size-fits-all" hypothesis is ridiculuous in light of what we know
about the way evolution happens.

Again, I find that I must point out that the expectations of
non-scientists regarding what science can accomplish are misguided. You
cite numerous human features and claim that we don't know why they
evolved. Well, you're right, we don't. We probably never will. The
"reason" why hominids became bipedal will always be up for grabs. What
we can do is generate models that are consistent with the majority of the
evidence. When we examine the issues in this manner, it is clear that
there are a number of models for the origin of bipedalism, a very
compelling model for the loss of body hair, etc.

Another analogy:

Hypothetical Elaine Morgan (HEM): All the dinosaurs were stolen by space

HEM's evidence: Paleontologists can't even agree on one of their poorly
constructed models for dinosaur extinction. It could have been due to
metorite strikes, or perhaps epidemic diseases, or their eggs were eaten
by mammals, etc. etc. But since they can't agree, my idea merits serious

Alex Duncan
Dept. of Anthropology
University of Texas at Austin
Austin, TX 78712-1086