SCIENCE AND FAITH: THE HOMINID FOSSIL RECORD

Lee A. Spencer, Ph.D.

Earth History Research Center

Southwestern Adventist University

Keene, TX 76059

Abstract— The fossil hominids are bipedal primates with a mixture of great ape (pongid), human, and pongid-human intermediate character states. There is a morphological continuum in skull and skeletal morphologies spanning those seen in the chimpanzee and anatomically modern man. Evolutionary/theistic evolutionary, progressive creation and “young-earth” creation interpretations of the data set are examined and tested. No interpretation remains unfalsified. Any interpretation held requires the exercise of faith. Science and faith not only are possible together, they are required.

Introduction

The cosmic questions of who we are and what our purpose in life is, if there is one, have been debated for as long as man has been in existence. So has the question of our origin. For millennia it has been commonly believed that a supernatural being or beings created man and this world. Over the last 150 years, this belief has been replaced by a naturalistic model in which man and this world came into being exclusively through naturally occurring processes. A conflict has ensued between those who believed in a supernatural being and those who do not. Few topics within the origins controversy engender more interest than that of man’s origin. Few topics better illustrate the intertwining of data and interpretation, science and faith, or cosmology and science.

Associated with the origins controversy, there is intense debate about what is or is not science, what constitutes religion and faith and how these factors combine to produce our cosmology. Because there are widely differing views on exactly what constitutes each of these terms, this paper uses the following definitions:

1) Data are directly observable characters and measurements. For the discussion of human origins the data set would include observations and measurements of skeletal remains, descriptions of sedimentary context, various chemical constituents, etc.

2) Interpretations are conclusions drawn from the data. For example, based upon microscopic grooves on the teeth (data), dietary modes may be inferred; based upon a measured ratio of ⁴⁰K/⁴⁰Ar, the number of calendar years required to produce that ratio may be hypothesized, etc. Some interpretations may appear to be self-evident. Conversely, there may be different and opposing interpretations of the same data set. Often in the scientific literature, data and interpretation are so intermingled that it is difficult to determine the actual data set, or only the interpretations are reported.

3) Science is the process of formulating testable (i.e. rejectable) hypotheses about the natural world.

4) Faith is the acceptance of statements, interpretations and/or hypotheses as true in spite of the lack of data or even the presence of contradictory data.

5) Cosmology is the belief system explaining the cause for the underlying harmony in the universe. Examples of cosmologies include naturalism where natural law is self-existent and is the sole cause for the underlying harmony of the universe, and variations of supernaturalism where there is a being above natural law. Evolution is the extension of naturalism that covers change through time. Theistic evolution, progressive creation, intelligent design, young earth creation, etc. are all variants of the supernaturalistic cosmology with differing levels or timings of intervention by the supernatural being. I know of no way to differentiate evolution and theistic evolution from observable data, so they will be treated together. Because cosmologies are belief systems, they are not directly testable and are hence outside the definition of science given above.

It is not the purpose of this paper to resolve the cosmological debate on human origins, but to show how our understanding of what man is depends completely… not on the data, but upon previously adopted views that form a previously accepted cosmology. Further, the exercise of faith is required for all cosmologies. We will first examine the human origin data set very briefly, then examine interpretations and hypotheses of the three most prevalent cosmologies: evolution/theistic evolution, progressive creation and neodiluvialism/young-earth creation.

A Summary of the Hominoid Data Set

(Details, Details, Details)

What Is A Hominid?

Linnean classification places all the apes with man in the superfamily Hominoidea. The Hominoidea can be distinguished from all other primates in lacking a tail and in having a wrist design that allows greater wrist flexibility and greater dexterity of the hands and feet than other primates. The Hominoidea is divided into three families, the Hylobatidae (gibbons), the Pongidae (orangutan, gorilla, and chimpanzee), and the Hominidae (man). The three families are distinguished from each other by different modes of locomotion and the anatomical structures necessary for that type of locomotion.

The Hylobatidae (also known as the “lesser apes” or gibbons) are brachiators, which means that they move by swinging arm movements with the body hanging below the arms.

The Pongidae or “great apes” are forelimb knuckle-walkers. The orangutan makes a fist and the first phalanx makes contact with the ground; the gorilla and chimpanzee use the second phalanx to make ground contact. The term “pongid” will be used throughout this paper to refer to this group.

The Hominidae (human beings) walk habitually upright and the hands do not normally touch the ground. Upright walking primates are known as “hominids” from the family name Hominidae and modern man, Homo sapiens, is the only living representative.

In the fossil record, there are a number of extinct, upright-walking primate taxa (hominids). The taxonomy of the fossil hominid specimens is hotly debated. Depending upon the author, there are nine to eighteen species placed within two to six genera. There is a general consensus, however, that all of the specimens can be placed within one of six general categories: the australopithecines, early “Homo”, the “erectines”, “archaic sapiens”, Neanderthals, and fully modern man. The australopithecines and early “Homo” are restricted to the African uppermost Miocene to Pliocene; the “erectines”, to the Old World Pliocene and Pleistocene; “archaic sapiens”, and Neanderthals to the Old World Pleistocene, and fully modern man to the Pleistocene and Holocene worldwide.

The classification of the hominid taxa used for this paper is modified from Tattersall (1993) and Wood and Collard (1999) and is as follows:

Family Hominidae

Insertae sedis Orrorin tugenensis

Subfamily Australopithecinae

Genus Ardipithecus

Species Ardipithecus ramidus

Genus Australopithecus

Species Australopithecus anamensis

Australopithecus afarensis

Australopithecus africanus

Australopithecus bahrelghazali (?)

Genus undescribed

Species “Homo” habilis

Genus Paranthropus

Species Paranthropus aethiopicus

Paranthropus boisei

Paranthropus robustus

Paranthropus garhi

Genus Kenyanthropus

Species Kenyanthropus platyops

Kenyanthropus rudolfensis

Subfamily Homininae

Genus Pithecanthropus

Species Pithecanthropus erectus

Pithecanthropus soloensis

Genus Homo

Species Homo heidelbergensis

Homo neanderthalensis

Homo sapiens

Data Set I: Hominoid Skull Characters

Living hominoids exhibit distinctly different skull morphologies. In the figure to the left is pictured an adult male gorilla skull. It can be characterized as having a prominent sagittal crest (ridge along the top of the skull), a large bony orbit (eye socket), and a prominent brow ridge. It also has a large flat facial area below the orbits and a protruding muzzle (prognathism) with large canine teeth.

Compared to the gorilla skull, the human skull lacks a saggital crest, has gracile orbits (thinner and smaller), and a short face, with no prognathism. There is no confusion about what is human and what is ape; there are no living morphologic intermediates.

However, if the fossil hominids are included, a different picture emerges. A gradation of morphological characters is seen ranging from those features that are mostly gorilla and chimp-like to those that equal modern humans. Character states examined here include endocranial volume, various cranial features and facial structure, placement of the foramen magnum, and construction of the face, mouth and teeth.

Endocranial Volume. Fully modern man has a brain capacity that averages about 1700 cc. The brain capacity of the pongids (gorilla, chimpanzee, orangutan) averages about 400 cc. There is no overlap between the smallest human brain capacity and the largest simian brain capacity. However, if we plot values including the fossil hominids, there is a gradation in endocranial volumes.

Cranial Morphology. Among the fossil hominids, we also see a gradation of cranial morphologies from an essentially pongid morphology to the modern human morphology. Large, bony eye sockets, a large nasal opening, and stout facial bones dominate the face of the pongid. The pongid facial pattern is seen in all fossil hominids except anatomically modern man.

Lateral View. A similar pattern is seen in lateral view. The pongid skull is characterized by a sulcus behind the brow ridges, prognathism and a protruding occipital region. Anatomically modern man lacks prognathism and brow ridges with the accompanying sulcus, and has a much less pronounced occipital bulge (see photo). The fossil hominids, including the Neanderthals, whose endocranial volume averages more than anatomically modern man, show the pongid pattern.

When viewed from the top, all of the skulls except that of anatomically modern man show a marked constriction just behind the orbital region. This constriction imparts a definite pear-shape to the braincase. Because the skull of anatomically modern man is inflated in the frontal area and has gracile orbits, the overall shape of the skull is more ovoid than pear-shaped.

Another character that is unique to anatomically modern man is the parietal bulge. When viewed from behind, the widest point of the skull of anatomically modern man is high, in the parietal region. The widest point of the pongid skull is close to the base of the skull, near the auditory region. All of the fossil hominids, including Neanderthal, have the widest point toward the base of the skull near the auditory region

1. Chimpanzee 2. Australopithecus africanus 3. “Homo” habilis 4. Kenyanthropus rudolfensis 5-6. Pithecanthropus erectus 7-8. P. soloensis 9. Homo heidelburgensis 10-11. H. neanderthalensis 12. H. sapiens

Foramen Magnum. In the pongids, the foramen magnum is located near the back of the skull so the head can be inclined and pointed forward during quadrapedal locomotion (knuckle-walking). In anatomically modern man, the foramen magnum is under the skull since the skull weight is born by the shoulders while walking upright. The fossil hominids show intermediate placement of the foramen magnum between that seen in pongids and anatomically modern man.

The Palate. In the figures above and below, also note the shapes of the palate. The pongid palate is rectangular with the widest part at the canines then narrowing backward into the skull. The human palate forms a parabolic curve with the widest part interior into the skull. The fossil hominid palates are intermediate in shape between the pongid and modern human morphologies. In all of the species except anatomically modern man, the premolars and molars form a relatively straight line. The axis of the line shifts from nearly parallel with the midline of the palate in the australopithecines to broadly divergent in the Neanderthals. Only the Mt. Carmel, Israel, Skul specimens, sometimes placed within the Neanderthals show the parabolic curvature of anatomically modern man.

The Mandible. The mandibles of the fossil hominids also share a number of structures with the pongids. The mandible of anatomically modern man has a well-developed protuberance called the mental eminence or “chin”. The pongid mandible lacks the mental eminence and tapers down and back toward the throat. Also seen in the pongid mandible is the “simian shelf” (see figure below), a lingual extension of bone behind the incisors. In the mandible of anatomically modern man, the bone development stops lingually with just enough bone to support the roots of the incisors. All of the fossil hominids including Neanderthal lack the mental eminence and have a simian shelf, although the shelf is relatively short in Neanderthal.

The Teeth. There are also dental differences. In general, pongid teeth are much larger that those of modern man. The canine of the pongids is so large a gap (the diastema) develops between the canine and incisors to make room for the opposing canine so the jaw can close. Modern man has a small canine and lacks the diastema. Except for Ardipithecus and some specimens of Australopithecus afarensis, all of the hominids share the human condition in having a reduced canine and lacking the diastema.

Morphological differences between the teeth also exist. The tooth directly behind the canine in the mandible of anatomically modern man (the p₃) is called the “bicuspid”. It has a well-developed metaconid along with the protoconid (see figure below). The pongids have only the protoconid on the p₃. The australopithecines have an intermediate morphology with a weakly developed metaconid. If you draw a line through the axis of the p₃ and another along the axis of the molar tooth row, the intersection of the two lines is nearly perpendicular in modern man, but forms an oblique angle in the pongids and australopithecines.

A major physiological difference between humans and apes is the development and emplacement of the teeth. The pongids grow faster and reach maturity earlier than humans. This is reflected in the timing of tooth replacement. Humans have a much longer period of parental care and nursing than the pongids. As a consequence, human infants have a delayed loss of the deciduous premolars (milk teeth). As a result, the adult human canine erupts and is in place before the adult m₂. In the chimpanzee, the adult m₂ is in place before the adult canine erupts (see figure above). The australopithecines and pithecanthropines show rapid dental growth rates similar to the pongids (Dean et al. 2004).

Data Set II: Hominoid Skeletal Characters

One of the characters used to classify the hominoids in different families is their mode of locomotion. There are distinct skeletal morphologies associated with locomotion. The pongids are tree climbers, but when on the ground, they are quadrapedal knuckle-walkers. The arms are as long or longer than the legs, the scapula has an orientation for supporting the body weight beneath the arms, and the fingers and toes are long and curved for grasping branches. The pelvis is shaped to support the legs and trunk in the bent-over posture necessary for knuckle-walking. Humans are habitual bipeds. The arms are shorter than the legs, the scapula is oriented for holding the arms by the side, and the fingers and toes are shorter and straight. The pelvis is shaped to support the legs and trunk in a vertical position and the knee locks the legs straight to minimize the expenditure of energy when standing. The australopithecines show intermediate character states between pongids and humans, the pithecanthropines intermediate between australopithecines and humans, and the members of the genus Homo are essentially like that of anatomically modern man in skeletal morphology.

The Limbs. There are a number of indices quantifying the proportional differences in the long bones and trunk of hominoids (Aiello and Dean 1990). As noted above, arboreal apes have longer arms than legs while modern humans have shorter arms than legs. The humerofemoral index quantifies this difference. If the limbs are of equal length, the index will be 100. Values greater than 100 occur when the arms are longer than the legs, values less than 100 occur when the arms are shorter than the legs. The australopithecines plot intermediately between the pongids and humans. The pithecanthropines and Homo species all plot together with the arms shorter than the legs.

The australopithecines also plot with the apes on the orientation of the scapula, an adaptation for arboriality. If a line is drawn through the axis of the ventral bar on the scapula and another through the glenoid cavity, the intersecting angle can be measured (Stern and Susman 1983). The apes have a bar-glenoid angle less than 140 degrees while humans have an angle of approximately 145 degrees. The australopithecines have an angle about 130 degrees. Like the humerofemoral index, the pithecanthropines and Homo plot together.

Another index of arboriality is the relative length and degree of curvature of the phalanges (fingers and toes). The phalanges of the pongids are relatively long and curved; those of modern man are short and straight.

The australopithecines are short like modern man, but curved like the pongids. The degree of curvature can actually be calculated and quantitatively compared among the various hominoids (Susman et al. 1984). The numbers confirm what was intuitively obvious from the illustration—the australopithecine phalanges have a pongid curvature. Members of the Homininae all have relatively straight phalanges.

The Pelvis. The morphology of the pelvis is a key in determining hominid locomotor posture. The pongid pelvis is relatively large with an elongate iliac pillar. The iliac crest is nearly parallel with the back and the angle of insertion of the femur. The human pelvis is much shorter and bowl-shaped. The iliac crest is oriented more to the side and forms a much more oblique angle to the back and insertion angle of the femur. With respect to the angle of the iliac crest and acetabular fossa, the australopithecine pelvis is intermediate in shape between the pongids and anatomically modern man. The pithecanthropines are intermediate between the australopithecines modern man.

Particularly important for posture are the vectors for support of the trunk and attachment of the legs. In the bent-over position of the trunk during quadrapedal locomotion, the elongate iliac pillars of the pongid pelvis support the back and abdominal tissues (at the expense of torsion ability). The angle of insertion of the femur allows considerable backward movement for stride length. When the pongid walks bipedally, the vectors change. The insertion angle of the femur requires that in order to stand, most of the backward movement of the leg has already taken place, meaning the that most of the stride must occur in front of the body axis. The human pelvic morphology has the vectors optimized for a vertical stance. The pelvis becomes a bowl to aid in visceral support, the shortened iliac pillar allows for lateral rotation or torsion of the trunk, and the insertion angle of the femur allows greater backward movement of the leg, increasing stride and balance when in the upright posture. The pelvis of all of the hominids has a shortened iliac pillar more like that of anatomically modern man. The intermediate angles for femur insertion seen in some hominids would restrict to various degrees the amount of backward movement of the femur, limiting stride and balance accordingly.

Data Summary

There is a gradation in cranial morphology between the pongid skull and anatomically modern man. The australopithecines have a very pongid-like skull; the pithecanthropines are intermediate between the chimpanzee and modern man; the Homo species, while they have a cranial volume as large or larger than modern man, also share many pongid-like characters. Post cranially, the picture is a little different. The australopithecines are intermediate in morphology between anatomically modern man and the pongids, the pithecanthropines are intermediate between the australopithecines and modern man, and there is little difference between of other hominids and modern man.

We will now look at the various hypotheses that have been postulated to explain the data from the three dominant cosmologies: evolution/theistic evolution, progressive creation and young earth creation.

Interpretation I: Evolution/Theistic Evolution

The Model

Through geologic time, mutations and natural selection will produce speciation events. A series of these events will lead from a common ancestor of the pongids and hominids to anatomically modern man.

The Evidence

A number of fossil hominid species have been described. Altogether, these species form a morphological gradient from a chimp-like species to anatomically modern man. The taxa appear in the fossil record in approximately the order expected if they had evolved.

Tests

If evolution occurred, the not only should the species appear in the correct order, but so should all newly evolved characters. Protein and DNA studies show the chimpanzee and man to be more similar to each other than either is to the gorilla, and the African apes and man are more similar to each other than to the Asian orangutan (Jones, Martin and Pilbeam 1992). Therefore, the hominids and the chimpanzee must share a common ancestor to the exclusion of the gorilla. The common ancestor of the chimpanzee and man cannot have any of the character states that evolved later as the two lineages diverged. Any characters shared by fossil hominids and the chimpanzee should have been found in the common ancestor of both. Testable hypotheses can then be built by analyzing the order of appearance of new characters.

The three oldest “hominids” Orrorin tugenensis, Ardipithecus ramidus, and Australopithecus anamensis all lack pelvic girdle and femoral specimens. Whether they were bipedal, and hence truly hominids, remains unknown. They are classified as hominids because the share certain dental characteristics with later species that were demonstrably bipedal. Ardipithecus ramidus is the most chimp-like of the fossil hominids. Orrorin tugenensis is older, but of doubted hominid affinity (Aiello and Collard 2001, Haile-Selassie 2001). All are too incomplete to use for broad comparisons. They share a number of characters with the chimpanzee including cusp morphology of the molars and curvature of the arm and fingers. They also share a number of characters with Australopithecus afarensis (Haile-Sedlassie 2001). Studies comparing them with later hominids have not yet been completed.

Australopithecus afarensis is the earliest hominid well known enough to draw phylogenetic conclusions. Because of this, it is usually placed as the basal taxon from which all other species are derived. The most common evolutionary hypothesis is that A. afarensis gave rise to A. africanus, then “Homo” habilis then to the pithecanthropines (Tattersall 1993). The characters in the first table below tend to support that hypothesis, but the characters in the second table falsify the hypothesis. The actual ancestor to “Homo” habilis would have to be like Australopithecus africanus but have prominent or moderate hollowing above and behind the mental foramen, have the height of the origin of the masseter muscle low, have the height of mandibular ramus relative to breadth low, have the most common site of anterior origin of zygomatic arch nearer the M¹, and have rare or absent anterior pillars. There is no known species with all the right character states in the right order (Skelton, McHenry and Drawhorn 1986). When you do this same procedure with all of the other hypotheses of ancestor/descendent relationships, the results are all the same -- there are no unfalsified hypotheses. In practice, the hypothesis that has been falsified the least number of times is accepted as being the closest to what is thought to have actually happened under the principle of parsimony.

Character States That Support the Hypothesis
Trait	A. afarensis	A. africanus	"H". habilis
Subnasal prognathism	pronounced	intermediate	reduced
Mandibular symphysis inclination	receding	intermediate	vertical
Flexion of cranial base	week	moderate	strong
Size of the posterior relative to anterior part of the temporal muscle	large	intermediate	small
Articular eminence of the mandibular fossa	weak	intermediate	strong/ cylindrical
Position/orientation of the foramen magnum	posterior/ angled	intermediate	More forward
Lingual ridge on lower canine	prominent	intermediate	absent
Number of lower-incisor mamelons	7	5	3


Character States That Falsify the Hypothesis
Trait	A. afarensis	A. africanus	"H". habilis
Hollowing above and behind mental foramen	prominent	reduced	moderate
Height of masseter origin	very low	intermediate	low
Height of mandibular ramus relative to breadth	low	intermediate	low
Most common site of anterior origin of zygomatic arch	M¹/P⁴	P⁴	M¹
Anterior pillars	absent	present	rare

This does not prove that evolution did not occur. You can always invoke the ad hoc postulate that the fossil record is incomplete and if it was complete, the actual ancestors and descendents would be known. Being ad hoc, it is procedurally the same as creationists saying that God did something. Faith is exercised in believing that evolution occurred in spite of there being no unfalsified hypotheses of descent.

The postulate of the incompleteness of the fossil record could be addressed. On the basis of probability, if the fossil record is incomplete by some factor, say 90% for example, and we go to different sedimentary basins, like Laetoli, Hadar, and Chad for example, then, by chance alone, we would have a 90% probability that each species recovered would be previously unknown. In fact, we find most of the species to be the same from these sites even though separated by hundreds of miles. All three basins have yielded specimens of Australopithecus afarensis as well as sharing most of the other mammal species (White, et al., 1984, Brunet, et al., 1995) The percentage of the fauna shared would give a minimum estimate of the completeness of the fossil record. For the sake of argument, say the three sites shared 60% of their fauna. Then the fossil record should not be less than 60% complete. It could actually be more complete if the missing or different taxa were different for some reason other than the completeness of the fossil record, such as biogeography. Whatever the actual calculated completeness turns out to be, that percentage of actual ancestor/descendent relationships should be recovered. The fact that none of the actual ancestors have been identified to date suggests that the ad hoc invocation of the “incompleteness of the fossil record” will continue as will the need to exercise faith that man evolved.

Interpretation II: Young-Earth Creation

The Published Model

Most young-earth creationist models classify the australopithesicens and “Homo” habilis as extinct apes (Lubenow, 1992, p. 166 and ch. 15) and the other hominid species as degenerate/diseased humans; they postulate that there are no transitions between the apes and modern man (Coffin, 1968; Lubenow, 1992; Marsh, 1958; Maynard-Smith, 1996).

Tests

Are Australopithecines Simply Extinct Apes?

The apes have traditionally been classified by their mode of locomotion. The lesser apes are brachiators, the greater apes are knuckle-walkers and the family of man is bipedal. The australopithecines are also bipedal. To classify the australopithecines with the apes requires redefinition of ape taxonomy. The australopithecines cannot be dismissed by simply changing the definition of what an ape is. They exhibit a combination of human and ape characteristics.

Are There Morphological Transitions Between the Apes and Man?

As noted above, there is a gradation of endocranial volumes from chimpanzee to human. There is also a gradation in overall morphology. The evidence presented above falsifies the assertion of two distinct (ape and human) morphologies as presented by Lubenow and others.

Is the Morphological Gradient the Result of Disease/Degeneration?

Many of the characters found in fossil hominids are also found in pongids, but not in anatomically modern man. No disease stretches the skull and face to produce prognathism and an occipital bun, removes the forehead and creates a sulcus, or creates large eyes with heavy, bony ridges. No disease takes away the chin and replaces it with a simian shelf. These are all characters found in pongids but not in anatomically modern man. In short, there is no “ape character” disease.

Results of the Test

The hypothesis that there are no morphological transitions between the apes and man has been falsified. The hypothesis that the fossil hominids are diseased humans is also falsified.

Interpretation III: Hybridization

The Model

Another “young-earth” model capable of explaining fossil hominids is that of multiple hybridizations between the pongids, humans and the results of previous crosses. Australopithecus could be the F1 of a human-chimpanzee cross; Paranthropus could be the F1 of a gorilla-human