Dialogue 8(1):12-15,34 (1996). --- Reproduced here with permission and the accompanying acknowledgements at the end, after being modified.
Evolutionary biologists are convinced that humans are
descendants of ape-like creatures. In spite of a number of disputes over
theories of ape-human lineages, paleoanthropologists
concur. Christian response to these assertions has been varied. Some Christian
organizations agree with the scientific community about the origin of humans
but maintain that at some time in the past human beings acquired an immortal
soul, moral sense, and/or the ability to reason. Others, including Seventh-day
Adventists, accept the Genesis account as the record of a historical event.
Where did Adam come from? Was he fashioned from the dust of
the ground by an intelligent Creator, or did he descend from an ape-like
creature? We know what the Bible says. Does the "book of nature"
agree?
Determining What Is Human
Although some pet owners might argue the point, traits
such as esthetics and moral sense, free choice, and complex speech set humans
apart from animals.1 Extinct human-like skeletons cannot provide us
with this type of information. Since scientists are not able to talk to the
organisms that are alleged to be our ancestors to determine just how human they
were, researchers rely on structural features of the fossil bones and genetic
information in modern apes and humans.
Modern humans are distinguished by several skull features.
Three notable characteristics can be easily recognized: (1) At
the front of the lower jaw, modern humans have a part of the jaw bone that protrudes
to form the chin. (2) The angle of the face is very flat because modern humans
lack a muzzle and have a non-receding forehead. (3) The upper portion of the
skull in modern humans is wider than the base of the skull. Determining whether
a fossil skeleton is a modern human does not appear to be too difficult.
The Hominids
Hominid is the name given to the bipedal primates,
including all of the species in the genera Australopithecus and Homo.
The australopithecines include the genus Australopithecusand,
for some researchers, Paranthropus. The
hominines refer to the members of the genus Homo.
The australopithecines are divided into two groups, based on
body type: (1) The gracile, small-boned, more fragile
ape-like forms include A. ramidus (the most
recent australopithecine find, currently proposed as the fossil closest to the
"missing link" or common ancestor of apes
and humans); A. afarensis (a
"community" of fossils has been found; one 40 per cent complete
skeleton is popularly known as "Lucy"); and A. africanus
(the "Taung Child," named for the locality
near which it was found). (2) The robust ape-like forms include A. aethiopicus (a skeleton with some distinct traits found
in A. afarensis, known as "Black
Skull"), A. robustus, and A. boisei. Some researchers place all of the robust forms
in the genus Paranthropus.2
The genus Homo, to which humans belong, has a number of
species assigned to it: H. habilis
(fragmentary material of a small species found near stone tools, known as
"Handy Man"); H. rudolfensis (gracile skull and bone material notably larger than H. habilis, even though it was formerly assigned to that
species); H. erectus (more than 200 fossil individuals popularly
referred to as erectines, including Java Man and
Peking Man); H. ergaster (skull and bone
material formerly assigned to the erectines and now
distinguished by lower jaw and tooth structure as a separate species, known as
"Turkana Boy"); H. heidelbergensis
("Rhodesian Man", an archaic H. sapiens previously identified
as an erectine, sometimes listed as H. sapiens heidelbergensis, a subspecies of H. sapiens; the
species has a larger cranial capacity than the erectines);
H. neanderthalensis (a robust species dommonly pictured as a "Cave Man", skeletal
remains frequently display evidence of trauma, sometimes listed as H.
sapiens neaderthalensis); and finally, H.
sapiens or H. sapiens sapiens (modern
humans).3
Research Approaches
In the search for human origins, three major groups of
scientists-- paleoanthropologists, evolutionary phylogeneticists, and molecular anthropologists--approach
the problem from three very different perspectives. Paleoanthropologists
focus on physical features of the hominid skeletons and on tool use.
Evolutionary phylogeneticists describe the similarities
or relatedness of organisms. Molecular anthropologists emphasize protein and
DNA similarities among the hominids.
Some hominid physical features. Paleoanthropologists are scientists who study exclusively
human origins. In comparisons of skeletal structures or morphological traits in
the hominids, they believe they have found several hominine and ape-like
features in these fossils. One of the most important species of the
australopithecines, Australopithecus afarensis,
exhibits these features.
Australopithecus afarensis, a
hominid also popularly known as "Lucy," has a hip joint,
that is not quite ape-like, not quite human. While it seems clear that
the australopithecines were not knuckle-walkers like modern apes, the hip
joints were rotated forward enough that they are not confused with modern human
hip joints. (One of the criteria that has been used to
identify the genus Homo is a fully upright walking posture.) Another
structure pointed out by paleoanthropologists as
evidence for an australopithecine link between apes and humans is the curvature
of the finger and toe bones. The australopithecine fingers and toes are not as
straight as human fingers and toes but the knuckle is not as simple as the
chimpanzee's.4 A number of these somewhat simian, somewhat human
features in the limbs of the australopithecines have been identified. In
addition, the decrease in the size of the teeth from the front of the mouth to
the back is a trait similar to the arrangement of teeth in the hominines.5
Human/ape-like features also are
found in the genus Homo. Homo habilis,
or "Handy Man," is included in the genus Homo primarily
because the fossil material was found associated with "tools." In
addition, H. habilis has a jaw that is very
human-like; however, its body skeleton resembles an australopithecine. The
specimens assigned to Homo rudolfensis are
included in the genus Homo because the skeletal structure is very
human-like; but the face and teeth look like robust australopithecines.6
Paleoanthropologists divide the erectines
into two species, based on the jaws and teeth, African location, and smaller
brain capacity of H. ergaster relative to the erectines from Asia.7
Several diagrams have been constructed to demonstrate the
proposed ancestral lineage of the hominids. The diagrams differ because the paleoanthropologists do not agree on the specific physical
features that should be used to identify ancestral relationships, timing of
divergence, and placement of new skeletal finds.8
Hominid relationships. Phylogeneticists
use cladistic methods (cladograms)
to describe relationships among organisms. Cladograms
are diagrams that arrange organisms in groups having shared characters,
describing organisms in terms of sister rather than ancestral relationships, in
a hierarchical form. In developing cladograms, phylogeneticists make three basic assumptions: (1) The
features or characters that make up the database can be arranged in a
hierarchical structure; (2) the data or chracters
selected accurately represent the organisms; and (3) there has been little or
no loss of defining characters.9 An example of the simplest cladogram was published in Current Anthropology in
1986 describing possible relationships among hominids based on 45 shared
characters out of 69 identified traits.10
Some characters used to develop the cladogram
appear in species in a different order than the majority of the characters
defining the cladogram. Phylogeneticists
select the cladogram with the least number of
out-of-order characters to develop "best fit" diagrams; consequently,
there is some disagreement over which characters best describe the organisms
and how they should be arranged in the hierarchy.
After using cladistics to identify
hierarchical relationships, numerous researchers incorporate this information
into hypotheses and develop phylogenetic schemes
depicting ancestral relationships for hominids. By 1993, at least six major phylogenetic schemes had been proposed for the hominids.
Since the discovery of A. ramidus, a seventh
scheme has been proposed. Much of the shuffling of species in these diagrams
represents disputes over the validity of attributing to human evolution the
various traits found in the skulls and teeth of the specimens.
The hominid molecular relationships.
Some anthropologists have studied molecular similarities among modern apes and
humans to develop hypotheses about hominid lineages. Some of these researchers
assume that mutations and changes occur at a constant rate in DNA. Numerous
studies, spanning more than 30 years, have tried to determine when various
living species diverged from related species, based on the assumption of
relatively constant rates of change in DNA, a "molecular clock."11
Interpretations based on the "molecular clock"
imply human origins occurred millions of years ago and assume that there is a
link between apes and humans. The time spans postulated for the ape-human
divergence range from
Others have narrowed their field of inquiry and compared the
mitochondrial DNA among human races, hypothesizing that the human line can be
traced to a single African population.
The Hominid "Lineage"
Australopithecines. In
the australopithecine group, A. ramidus (the
most recent find) and A. afarensis (Lucy) are
both considered ancestral,13 whereas A. africanus
(Taung Child), listed as recently as 1993 as
ancestral,14 continues to be disputed as part of the direct line.15
Hominines. In the Homo genus, H. habilis (Handy Man) remains problematic but is listed
outside the human line by Wood, and inside the human
line by McHenry.16 The gracile form of H.
rudolfensis once replaced H. habilis in the human lineage but now is also excluded
by some workers. H. erectus (Peking Man, Java Man) should currently
listed as "offline" according to Tattersall17 due to the
fact that a portion of its skull structure is too robust.18 Some
researchers list H. ergaster as one of the
preferred "links," although others still consider H. ergaster as a separate species and continue to include
these organisms with the erectines in the ancestral
line. Finally, H. heidelbergensis is regarded
as ancestral to both modern humans and the neanderthals.19
Evolutionary Hypotheses Falsified
A recent diagram published in Nature illustrated
some current paleoanthropological conclusions in
regard to ancestor-descendent relationships for hominids. The common ancestor
for hominids and apes is still missing. A. ramidus,
A. afarensis, and H. heidelbergensis
are all clearly listed as "links" in the lineage. However, it appears
from the diagram that H. habilis, the erectines and H. neanderthalensis
are all considered off-line. 20
Using standard scientific methods, researchers test their
hypotheses, rejecting those ideas shown to be false. In studies of human
evolution, standard scientific methods may not be adhered to by some workers.
As noted earlier, A. afarensis has unique
traits that actually preclude them from being included among our ancestors. One
cladistic study identified 69 traits that are
expressed differently among the species in the "human lineage." Of
these, only 45 support the preferred evolutionary hypothesis.21
The remaining 24 characters
contradict this preferred evolutionary hypothesis. The preferred hypothesis was
selected by the researchers as representing the probable path of "human
evolution" because it had been falsified the least number of times. As a
result--and to their credit-- other researchers have questioned the validity of
A. afarensis as a human ancestor.22
The reversal in robustness that occurs with the inclusion of H. erectus
in the "lineage" is another factor that is inconsistent with the
current hominid evolutionary hypothesis.
Conclusion
What does the "book of nature" tell us? All
hominid evolutionary hypotheses have been falsified. To be fair, this does not
rule out the evolutionary theory (new specimens may be discovered to resolve
the conflicts); therefore, it is not appropriate to announce to the world that
"Evolution has been refuted," based on the incongruence of current
hypotheses.
If all of the hominid evolutionary hypotheses have been
falsified, how does one interpret the fossil material? Comments by Wood (1992)
illustrate what can be perceived as a blending of characters: "Whereas H.
habilis sensu stricto [in the strict sense] is hominine with respect
to its masticatory complex [mouth and jaws], it
retains an essentially australopithecine postcranial skeleton [body]. Homo rudolfensis, on the other hand, apparently combines a
later Homo-like postcranial skeleton with a face and dentition [teeth]
which are adaptively analogous to those of the 'robust' australopithecines,
especially, P. boisei." Many characters
that occur together in the australopithe-cines and in
the hominines represent a mosaic of traits. Some Christians would interpret
these organisms to have resulted from degeneration of the human form due to the
entrance of sin. Another interpretation restricts the term human to
anatomically modern humans and assigns the rest of the fossils to non-human
created kinds. A broader interpretation of the term human would accept
at least some of the fossils as other created subspecies of humans. Whatever
these creatures were, it is obvious that there are problems with almost any
interpretation of these fossils. Given the current database, caution is
warranted. Indeed, it would be premature to draw any definitive conclusions
with regard to the origins of these organisms and their relationship to the
Genesis record.
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I would like to express my appreciation to Dr.