Re: Semantics? (Homo species)
Julia E Smith (jesst2+@pitt.edu)
20 Dec 1996 15:30:41 GMT
In article <19961219041200.XAA10065@ladder01.news.aol.com>,
Prockstroh <prockstroh@aol.com> wrote:
>
>I've been wondering why it is that, whenever someone finds a new jawbone
>or skeleton or whatever that resembles us in some way, they call it Homo
>boisei or Homo habilis or Homo XXX, rather than just plain old Homo
>sapiens. Usually, the difference is based on a slight skeletal difference
>(jawbone? skull size? Physical anthro. is not my strong point).
>
>If you look at, say, a Chihuahua skeleton compared to that of a
>Rottweiler, you see all kinds of differences, but they're still the same
>subspecies. So why are humans put in all these different groups?
I'm going to go off on a brief tangent, then I'll get back to Homo. I
would observe that the only places in which we see the kind of variation
(Chihuahua to Rottweiler) that we see in dogs is in situations in which
there has been a *strong* breeding pressure. Humans have been much better
at exerting strong breeding pressures than nature ever was. About the
only way to get the kind of variation that we see in dogs is to separate
two different species and let them breed for a long time. But usually
that leads to speciation.
What's speciation? We define species as distinct today if they do not
normally interbreed. That is not to say that we can't force them to breed
in captivity (we've produced lion/tiger hybrids, for instance), but that
they would not exist in nature. That's hard to determine, however, in
fossil populations. We can't just try breeding them, so we argue a lot,
and guess a lot, and change our minds a lot.
OK, back to fossil humanoids. Here's the population of fossil "people" as
most people see it today:
"archaic" Homo sapiens (300k to 100k)
Homo sapiens sapiens (100k to today)
Homo sapiens neandertalensis (200k to 40k)
Homo erectus (until last week, we would have said 1.5 mya to 300k)
Homo habilis (2mya to 1.5mya)
Australopithecus africanus (2.5mya to 1.5mya)
Australopithecus robustus (2.5mya to 1.5mya)
Australopithecus boisei (2.5mya to 1.5mya)
Australopithecus afarensis (4-5mya to 2.5mya)
So, is this a lot? We have 3 species of Homo and 4 species of
Australopithicenes, over the course of 5 million years. To compare,
around 15 million years ago, there were some dozen species of apes
(Proconsul, Ramapithecus/Sivapithecus, Driopithecus, Gigantopithecus,
Kenyapithecus, to name 5 *genera*). The differences between these species
are fairly pronounced, mostly in terms of brain capacity, but also in
terms of other cranial features (if you've seen A. africanus and A. boisei
side by side, you've seen an amazing difference in sagital crest in
particular and robusticity in general).
Having said that...in earlier days (as recently as the '60s), people
tended to create new genera at the drop of a hat. Thus. A. boisei was
orignially Zinjanthropus boisei; a variety of other names have come and
gone. Indeed, there was a time when every new fossil got a new
name. During the '60s, however, David Pilbeam and Elwyn Simons cut
the number of genera and species down to their current levels.
The fight of the last 20 years have been between two factions that
might be identified as the "Old Homo" faction and the "Young Homo"
faction. Some people have suggested that we might find another Homo
species older than habilis, while others have tried to dismiss even H.
habilis as not separable from A. africanus. This arguement (usually
between Richard Leakey and Donald Johanson) can well give you the idea
that these species consist of only a few skeletons each. However, at this
point, we've got a lot of each.
I can't explain why your professors aren't willing to sit down and explain
this to you. Most of this was off the top of my head; that which wasn't
I got from:
Roger Lewin. 1989. Human Evolution: An Illustrated Introduction.
Second edition. Blackwell Scientific Publications.
Hope it helped.
Julia Smith
jesst2+@pitt.edu
University of Pittsburgh
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