Tree pruning -- Resolving Power of Instruments Used
H. M. Hubey (email@example.com)
24 Sep 1995 01:43:44 -0400
I had briefly mentioned this earlier. Here are some lines from
From Science News, September 2, 1995
PRUNING THE FAMILY TREE
A controversial study sends many hominid species packing.
by Bruce Bower
Hominids evolved gradually from one species to another, these
researchers propose. Dispersed groups of each human ancestor interbred
from time to time, adding layers of anatomical variety to a common
biological theme. Fossil investigators often see two or more species
where only one existed, they say, because they tot up minor skeletal
differences that arose in biologically unitary hominids.
"I know it sounds outrageous, but we have good evidence that there was
no more than one species at any one time in the hominid family -- from
a hypotethical ancestral ape to modern humans," contends Maciej
Henneberg, an anatomist and paleontologist at the University of the
Witwatersrand Medical School in Johannesberg. "Multiregional evolution
goes back to the beginnings of the hominid lineage."
Henneberg and J. Francis Thackeray of the Transvaal Museum in Pretoria
present their findings in the current Evolutionary Theory (vol.16, no.1)
Henneberg and Thackeray maintain that proposed hominid species living
at roughly the same times displayed no more anatomical variation than
our current species, Homo Sapiens, in two crucial measurements --
cranial capacity (and indirect marker of brain size) and body size.
To better understand the cranial variation in a sample of three ancient
hominid skulls, the researchers randomly selected samples of three
skulls from a worldwide collection of 10,000 modern H. Sapiens skeletons.
They repeated this sampling 1,000 times and calculated an acceptable
range of variation. Henneberg and Thackeray then repeated this
statistical exercise for sample sizes of 4 to 19 skulls.
They found, for example, that the extent of cranial variation in
modern human samples met or exceeded the corresponding variation
in 10 Australopethicus africanus skulls, 12 skulls from both
A. africanus, and A. afarensis, 13 skulls from early Homo and the
robust australopethicines (considered a separate hominid genus by
some scientists), 19 australopethicines from several commonly
accepted species, 18 H. erectus skulls from Africa and Asia, and
10 Homo specimens from various regions dated at 1 million to 500,000
Any of these samples could therefore have come from a single species
composed of separate populations bearing distinctive features, as
occurs in modern humans, Henneberg maintains.
The range of body heights and weights in different sets of hominids
that lived at about the same time also falls within the spread of
modern humans, the South African researchers hold. Even fossils
grouped by their ages rather than their species designations -- such
as those from 4.5 million to 3.1 million years old or from 1.75 to
1.25 million years old -- differ no more in extent of thier body
sizes than do modern humans.
The findings indicate that species have emerged over long periods in a
single hominid lineage, according to Henneberg.
Conclusions such as that of the South African scientists undermine
arguments that some hominids, such as Asian H. erectus and Neandertals
did not contribute to human evolution, according to Thorne. Instead
anatomically distinct races capable of interbreeding have evolved
over at least the past 2 million years, in his view.