Re: A Specification for a

Alex Duncan (
1 Nov 1995 15:28:42 GMT

In article <> Paul Crowley, writes:

>However, I'd like to step back further and say that while we have no
>fossil evidence, it is parsimonious to assume that all the features
>that make a species distinctive appeared at the point of speciation,
>if they were not present in the CA. So it's parsimonious to assume
>that knuckle-walking appeared in the CA of the gorilla and the chimp
>when it split off from other apes; that social behaviour and an
>omnivorous diet appeared when chimps split off.

Our current understanding of evolution is that it is ALWAYS happening.
It has been demonstrated that there are some genetic loci in which no
change occurs for short periods of time (or even very long periods of
time, e.g., gene for histone). However, the norm is for evolutionary
change. In other words, your "parsimonious" assumption is incompatable
with the way the world is observed to work.

Assume that we had no fossil evidence for human evolution. Following
your assumption, we would posit that at the point of speciation from the
CA, fully modern humans appeared, and then didn't change for 5 - 6 Myr.

>Nakedness is a most distinctive feature; so is bipedalism. Both
>would seem to represent very particular adaptions to a new form of
>life. Our job is to identify that form of life. We know large
>brains came later. Maybe, if we could link nakedness with large
>brains we could escape the problem; but until we have such an
>explanation, a link with bipedalism can be (weakly) assumed.

Frankly, I don't think this can even be "weakly" assumed. When we
examine the fossil record, we see a gradual accumulation of the features
that make us "human." It is true that we are only examining skeletal
evidence, but your "weak assumption" would force an unparsimonious model
in which all of the soft tissue features of humans appeared at the time
of speciation from the CA, and skeletal evolution proceeded at a more
leisurely pace. It seems unlikely, to put it mildly.

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