|Is there fossil evidence
of "missing links" between humans and apes?
Did ancient humans live millions of years ago?
Dr Marvin L Lubenow, whose article Paleoanthropology in Review (1996, CEN Technical Journal, 10, 1:10-17) has a B.A. from Bob Jones University, a M.Th. from Dallas Theological Seminary and a M.S. in anthropology and palaeontology from Eastern Michigan University. He is a Professor Emeritus at Christian Heritage College, San Diego, where he recently received his doctorate. .He is author of Bones of Contention (1991, Baker Book House, Grand Rapids, Michigan). I reviewed Bones of Contention in 1993 (Groves, C. Review: postmodernism in pseudoscience. The Skeptic, 13, 4:20-22). I was interested that he does not underplay the richness of the human fossil record; he is less prone to paranoia than many creationists; and he obviously has little sympathy for the knee-jerk "analyses" of Duane Gish. Despite the fact that in many respects it represents a considerable advance in creationists treatment of palaeoanthropology, the book shows little understanding of many fields, notably evolutionary theory, or taxonomy, or population variation; it is, like every other creationist tract you can think of, full of direct quotes from "evolutionists", making them appear to be making dreadful admissions; and it relies more on sniping at details than at approaching the broad picture. Another creationist (Cuozzo, J., 1998, Buried Alive, Maaster Books) has since reprimanded him for ascribing the morphology of Neandertals to pathology.
I know that Lubenow has read my review of his book, but in his CENTJ/www article he acts as if he had not, and continues to make the same errors of understanding.
He begins with Ardipithecus ramidus, described five years ago from 4.4-million-year old deposits at Aramis, Ethiopia, by White et al. (White, T.D., Suwa, G. and Asfaw, B., 1994, Nature, 371:306-312). This has been lauded as "the missing link" by many palaeoanthropologists, including myself in a popular article (Groves, C., 1995. Gift from Aramis 'the missing link'. The Canberra Times, April 11,1995, p. 7). Lubenow takes great exception to these interpretations, claiming that there is reason to suggest that it is actually a form of pygmy chimpanzee. (Note, of course, that Lubenows entire article contains no actual anatomical comparisons of A.ramidus, or any other fossil, with chimpanzees of any kind).
Lubenow quotes my article, including the following passage:It doesn't exist alone: it's in a context of all those hundreds of other pre-human remains. The ones that are slightly younger than ramidus are slightly more human like; those that are younger still are more human like still, and so on. It's a graded series from then to now.
This quote is absolutely correct, and I stand by it. But Lubenow, having quoted it, then acts like all creationists and completely ignores the message, contenting himself with the usual sniping: "A.ramidus isnt an ancestor because...", "Homo habilis isnt an ancestor because...", and so on. The very clear picture, that as you come towards the present day the more human they look, is something that simply must not be admitted by any creationist, or their whole house of cards falls apart.
I then listed the most widely recognised fossil species in the human clade, omitting for simplicity mainly the "robust australopithecines" (Paranthropus spp.). Lubenow appears incautiously to mistake this for a " progression": he appears to think that I am saying that Neanderthals, Homo erectus, Homo ergaster, Homo rudolfensis, Homo habilis, Australopithecus africanus, and Australopithecus afarensis form an ancestor-descendant sequence. In fact, in my article I took pains to stress "cousins as well as ancestors".
Lubenow next attacks the date of A. ramidus; if substantiated, this 4.4 Ma date extends human ancestry farther back in time. So, he says, it is claimed to be the earliest known hominid, and explains that "Hominid' is an evolutionary term referring to all fossil individuals who are believed to be direct human ancestors, including the australopithecines, especially those believed to have walked erect". There are several things wrong with this explanation:
White et al wrote of Aramis: "All hominid specimens were surface finds ..." This does not mean that they were rolled in from elsewhere; in fact, their condition indicates otherwise (there is a whole field called Taphonomy which is devoted to the study of how fossils got to be where they are). The date was also, at one point, queried by Kappelman and Fleagle (1995, Nature, 376:558-559), and satisfactorily answered by Wolde Gabriel et al. in the same edition of Nature. Lubenow misunderstands Wolde Gabriel et als reply; he thinks he has caught them out in an admission that they were led to the 4.4 ma date by "biochronological comparisons" of fauna from other places:
(1) "Hominid" is not an evolutionary term but a taxonomic one; it is a vernacular from Hominidae, the name of the zoological family which includes humans.
(2) The family Hominidae is increasingly taken to include the Great Apes (orangutans, gorillas and chimpanzees) as well as humans. The human clade is, in this taxonomic scheme, regarded as at most only a Tribe, Hominini, within the Hominidae.
(3) The old Hominidae (= the tribe Hominini) includes not only fossils "believed to be direct human ancestors". Something that creationists seem not to understand is that "evolutionists" do not believe that all fossils related to a living species are its ancestors. Read again what I said: "cousins as well as ancestors".
(4) It happens that all of the more completely-known fossil taxa in the Hominini were bipedal in at least their predominant locomotor pattern. But clearly bipedalism developed in the human clade after it separated from the closely related chimpanzee clade. So the discovery of fossil hominin species that did not walk erect can be anticipated.
In other words, an estimate was made of what the date should be based on the evolutionary development of similar fauna found elsewhere.
This is a travesty. The full sentence reads:
Our first published chronological assessment was made on the basis of statigraphy, structural relationships, biochronology, 40Ar/39Ar dating and palaeomagnetic data.
Later, they note that:
Biochronological comparisons with fauna from Maka/Belohdelie provided the first clue that the Aramis hominids were older than those from east of the modern Awash River.
This is an account of the history of the growth of understanding of the dating of the deposits; it is not some kind of admission of circular reasoning, of making the 40Ar/39Ar dates fit. They then go on to explain in some detail why Kappelman et al. misunderstood the argument about the dates.
[As an aside, there has been much speculation, informed and uninformed, about the reasons for the delay in publishing further information about Ardipithecus. White presented a paper at a congress in South Africa in late June/early July, 1998, attended by about 750 palaeoanthropologists and human biologists. The paper was illustrated by slides of the site and some of the fossil material. The site is flat, stony and arid; the fossils are scattered over the landscape, friable in the extreme, and difficult to collect, let alone to preserve. It is true that remains of at least 50 specimens ascribed to A.ramidus have been collected, but these will take years to preserve, fit together, study and describe.]
For Lubenow, this seems to be an attempt to make the radiometric dates fit the faunal
analysis, which reminds him of the polemic over the date of the famous skull KNM-ER 1470,
from Lake Turkana in Kenya. There was, he claims, such disagreement between radiometric
and other dating techniques that it was finally dated by "biochronological
comparisons", in this case the stages of evolution of pigs in East Africa.
Not true, actually. What is true is that the palaeontologists argued for some years for restudy of the K/Ar dating techniques, because their faunal analyses suggested that the date of the KBS Tuff, below which ER 1470 was found, was anomalous. Ian McDougalls group finally managed to date material from which all contaminants had been eliminated, and showed that the palaeontologists were correct.
[Incidentally, the significance of these "stages of evolution of pigs" is passed over in silence by Lubenow. Surely he is not making a tacit admission that pigs did evolve! In creationism, neither humans nor pigs should evolve; and yet, there they are - several lineages of them, abundantly represented - in sites like Omo/Shungura, whose stratigraphy and dating are entirely uncontroversial, evolving away and eventually either becoming extinct or ending up as the modern Bushpig, Warthog and Giant Forest Hog. Elephants, incidentally, did the same thing, and their remains are likewise sufficiently numerous that their evolution can be tracked in great detail between about 4 and 1 million Ma.]
He then turns to the question of the thickness of the enamel on the fossil teeth, offering this quote from White et al.:
A comparison of this ratio of enamel thickness suggests that A. ramidus may be characterized as intermediate between the chimpanzee and the A. afarensis/africanus/early Homo conditions
- contrasting it with this from Peter Andrews:
... all other hominids, including modern humans, have relatively thick enamel... . So the thin enamel of ramidus is more of what you'd expect from a fossil chimp.
He then accuses White et al. of "using an improper diagnostic tool" to give A.
ramidus the status of "missing link", because of studies that have shown
great individual (including environmental) variation in enamel thickness in primates. But
this is not what White et al. are doing - enamel thickness itself is not the basis for
White et al.s, or anyone elses, phylogenetic placement of A,ramidus.
The thin enamel was actually a surprise, and led Andrews, as quoted, to reassess the
phylogeny of enamel thickness in the Hominidae.
Then there is the evidence of the first deciduous molar (dm1) of A. ramidu. Lubenow quotes White et al.:
The dm1 has been crucially important in studies of Australopithecus since the discovery of the genus 70 years ago, and has been used frequently as a key character for sorting apes and hominids. The Aramis dm1 is morphologically far closer to that of a chimpanzee than to any known hominid.
This, Lubenow claims, means that, like Peter Andrews, they are virtually admitting that
A. ramidus is really a fossil chimpanzee! What nonsense. White et al. make it clear
that, chimplike though the mandibular dm1 of A.ramidus may be, it does not
fall within the range of variation of chimpanzees. Peter Andrews and I confirmed this
together, using the Natural History Museum (London) sample: the tooth is more like that of
a chimpanzee than those of orangutans, gorillas, humans or australopithecines, but it is
not, repeat not, identical. It differs from chimp dm1, as White et al.s figures
indeed show, in the human/australopithecine direction.
Finally - bipedality. Lubenow thinks this important because, according to him, "the definition of a hominid [read hominin] involves bipedality". Little postcranial material was discovered by the time of the 1994 description (we understand that it has been since then), so evidence for bipedality must be sought in the basicranium. In humans the foramen magnum is beneath the centre of gravity of the skull; in quadrupedal mammals (including Great Apes, though these are somewhat intermediate), it is further back. Two basicranial fragments in A. ramidus "...evince a strikingly chimpanzee-like morphology ..." according to White et al., though the position of the foramen magnum "...may correlate with bipedality although this remains to be demonstrated". As Lubenow thinks that to be a hominid (hominin) you must be bipedal, and as White et al. admit that bipedality has not been demonstrated, "a refutation", he says, "is hardly necessary".
No sir, bipedality would not be "essential" if A.ramidus is a hominin. It is intermediate, in the sum total of its known parts, between chimpanzee and human; that is all one needs to know.
A DIAGNOSTIC PROBLEM
Henry Gee, a senior editor of Nature, now gets a guernsey from Lubenow. Gee "is honest enough to admit" the existence of a problem: "... with creatures as primitive as A.ramidus it will be almost impossible to tell the difference" between it being on the human or some other line. Lubenow takes this to mean that Gee is admitting that it might actually be a chimpanzee.
Note well: "on some other line". Chimpanzees, too, had ancestors: they
have not remained unchanged since they and we diverged from the common ancestor. On the
evidence as we have it so far, three possibilities exist for the phylogenetic position of Ardipithecus:
(1) it is part of the human clade, (2) it is part of the chimpanzee clade, (3) it is the
common ancestor, or close to it. While, and this is what Gee is saying, any of these
hypotheses can be entertained, the balance of evidence supports the first. What it
certainly is not is a chimpanzee, either common (Pan troglodytes) or pygmy (Pan
Lubenow sums it up: A. ramidus is not proof of evolution. Only if evolution is true can it be given any significance in human ancestry. If evolution is not true, it becomes just a "fossilized chimpanzee" - and, as he thinks he has shown, this is a more logical interpretation of it.
Now, in my article, I stressed that A.ramidus by itself is not "proof of evolution". Read the following quote (which Lubenow himself has already quoted, earlier on, but not taken note of):
In case any creationists are reading this, let me warn them not to seize on its apishness, or on the natural caution of scientists, to say 'its just an ape'.
Then follows the section which he cited above, "It doesnt exist alone..."
A. RAMIDUS AND PYGMY CHIMPANZEES
Is A.ramidus actually a pygmy chimpanzee, he now asks? The pygmy chimpanzee, or bonobo (Pan paniscus) is a rare species confined to the rainforests south of the great bend of the Congo/Zaire River. There is argument about the precise relationship of Pan paniscus to the common chimpanzee (Pan troglodytes), and Lubenow seizes on this:
Although the two are placed in a separate species, it is not known if the pygmy chimp is just a scaled down version of the common chimp, a phyletic dwarf, or if it is distinct enough to be placed in a separate genus-as blood group serology studies suggest.
If we cant even solve questions like these, he says, concerning living apes of which we have whole skeletons for study, we are within our rights to challenge the status of A. ramidus, known from 17 fossil fragments, as the "missing link" proving human evolution.
(His reference for this taxonomic/phylogenetic uncertainty is a review by Leutnegger of a 1984 book called The Pygmy Chimpanzee, edited by Randall L.Susman. Leutnegger is citing a chapter in that book by Socha, who is actually the only person since the 1950s to suggest that Pygmy Chimpanzees are generically distinct from Common Chimpanzees.)
Anyway, he goes on, Adrienne Zihlman has shown that the pygmy chimp is remarkably like "our alleged early ancestors", and he quotes her: "Except for the pelvis [a big "except", isnt it?], the P. paniscus skeleton shows a striking resemblance to fossils of the earliest hominid Australopithecus." Of course, as he admits, she does not believe that australopithecines were actually just pygmy chimps, rather that the most recent common ancestor looked rather like a pygmy chimp. So that should be that, shouldnt it, for A.ramidus and australopithecines being pygmy chimps?
THE BIPEDALISM PROBLEM
Next, bipedalism. Lubenow quotes Carol Ward: "The origin of hominid bipedality is one of the most controversial issues paleoanthropology", and Bernard Wood: "Bipedalism is a fundamental human characteristic yet virtually nothing is known about its origins." He cites Wood citing Hunt on the distinction between bipedal posture and bipedal locomotion; most chimp bipedalism is postural, related to feeding, very little to locomotion, and, according to hunt, early hominids (hominins), such as Lucy, were postural bipeds, and locomotor bipedality came only with the appearance of Homo.
Sorry, but this is a misquote. Wood writes as follows, summarising Hunts argument:
postural biped, he suggests that an emphasis on locomotor bipedalism did not appear until the emergence of early African Homo erectus, or Homo ergaster around 1.9 million years ago". Emphasis on - note that.
Whereas he provides cogent functional anatomical arguments that A.afarensis was a
The short paper by Wood, quoted by Lubenow, was written as a discussion of two other papers, the one by Hunt being "in press" in Journal of Human Evolution. In principle, what one does, rather than rely on a secondary source, is to find the primary source. Sure enough, in the March 1994 issue of JHE (26, 3:183-202), we find Hunts paper published. What does he say? On p.195 we find: "[in Australopithecus afarensis] a lower frequency of bipedal walking is suggested compared to modern humans", and on pp.198-9, this:
Although bipedalism may have been virtually the only terrestrial locomotor mode in A.afarensis, poor bipedal mechanics and compromises that improve arboreal competence suggest a role for locomotor bipedalism that is relatively reduced compared to modern humans. The small-tree postural feeding hypothesis reconciles the presumed contradiction between bipedal lower body morphology and arboreal upper body anatomy in A.afarensis. It also suggests that early hominids may not have been reluctant, half-evolved bipeds, but rather they had a fully evolved, unique adaptation for both terrestrial and arboreal bipedal gathering that was unlike that of any extant species, including humans.
Hunt here is supporting the (still controversial) hypothesis that australopithecines were not only terrestrial and indeed locomotor bipeds - which no specialist, none at all, disputes - but were efficient at arboreal locomotion as well; in fact, he was one of the first to argue in detail for this model.
No fossils chimpanzees have ever been identified. Lubenow claims that they have, but "the blinding power of a naturalistic evolutionary philosophy, and the determination of evolutionists to find evidence for it" has caused "evolutionists" to misidentify them - as australopithevines and as Ardipithecus ramidus.
RECENT TRENDS REGARDING HOMO HABILIS
"The demise of Homo habilis", Lubenow claims, "has been amazingly swift", and he identifies the following problems:
(1) There is a large range of variability in cranial size. This has been identified as sexual dimorphism, or as indicating that two or more species are involved. [Correct]
(2) There is equally a large range of variability in the post-cranial material. [Correct again]
(3) What Lubenow calls "the problem of reversals". If Homo habilis was ancestral to Homo erectus which was the direct human ancestors, you have to go from the thin-walled and high-domed cranium of Homo habilis to the thick-walled and low-domed cranium of Homo erectus and then back to the thin-walled and high- domed cranium of modern humans. "Reversals are not supposed to happen", he tells us, "in an evolutionary sequence.
What? Reversal is a well-established evolutionary phenomenon. It is one of three ways in which evolutionary change can be non-homologous; the other two are parallelism and convergence. Together they are dubbed Homoplasy. This is the sort of thing I meant when I said that Lubenow simply does not know evolutionary theory.
So, what used to be classed as Homo habilis is now fairly generally split into two or even three separate species. What is the problem? Lubenow seems to feel that this is devastating to the whole concept of human evolution, Im not sure why. It seems to involve his misapprehension that somehow the transition that is needed by "evolutionists", between australopithecines and Homo erectus, has fallen away. He sees this quote by Milford Wolpoff as a "confession":
... the phylogenetic outlook suggests that if there weren't a Homo habilis we would have to invent one;
- and says that this is precisely what has happened!
Alas, Lubenow in his zeal has completely misinterpreted Wolpoff, who is here reviewing a huge monograph by Phillip Tobias (1991) entirely devoted to Homo habilis; and this, I suppose, is what leads him to omit Wolpoffs next sentence, which reads:
With its ancestry circumscribed by the evidence for a lineal split reflected in the discovery of a 2.6 myr Australopithecus boisei... , and the clearly recognizable descendent species Homo erectus 1.8 myr or older, there is a distinct species with a beginning, an end, and, as Tobias has shown herein, a set of diagnostic features and a unique evolutionary role.
What "confession" is there here? As Wolpoff says, Homo habilis is precisely what might have been predicted.
RECENT TRENDS REGARDING HOMO ERECTUS
The next "stage" in human evolution, in Lubenows unilineal scheme, is Homo erectus. He thinks it absolutely damning that the "more than 222" known specimens of Homo erectus have "stubbornly resisted efforts" to place them "into a neat evolutionary continuum".
Problems with the species, he tells us, include its origin, its fate, and the lack of evolutionary change over at least a million years. Concerning its origin, he mentions Johanson and Whites view that "the three foot tall Homo habilis" at 1.8 Ma "evolved into [six foot tall] Homo erectus by about 1.6 Ma". Lubenow feels that this is ludicrous: to double in size in such a short time "is asking too much even of the punctuated equilibria model".
Why? As indeed he notes, there are indications that Homo erectus - Homo ergaster, actually - was already around over two million years ago.
Ancestral taxa surviving alongside their descendants - Lubenow again does not know evolutionary theory. I already pointed this out in my 1993 review of his book.
Lubenow sees Bernard Woods "proposal" of two new species as an attempt at a solution of this imagined problem. (Actually, Wood was reviving two previously proposed species. Homo rudolfensis was first proposed (as Pithecanthropus rudolfensis) by Alexeev in 1986, and Homo ergaster by Groves & Mazak in 1975. Most authorities now accept H.rudolfensis; on H.ergaster the field is split - some accept it as a separate species; others regard it as the same as H.erectus).
The origin of Homo ergaster (or African H.erectus, if you are being conservative) is not known. There is a gap, filled by just a few scarps, between about 2.5 and 2 ma. There is no dark secret about this. Until the mid-1970s, there was a big gap prior to 3 Ma; this is now filled, just as the post-2.5 gap will be filled (and is, slowly, being filled, in fact). But Lubenow has his own hypothesis about the origin and fate of Homo erectus: the whole thing - that distinctive cranial form - "may be the result of the environment of the post-Flood Ice Age".
It is at this point that we can bring in another creationist, Jack Cuozzo. In his (admittedly rather bizarre) book, Buried Alive), he warns against not taking fossil hominin morphologies seriously, and specifically mentions Lubenow in this regard (concerning, in this case, Lubenows proposal that Neandertal morphology is not real, but due to pathology).
LACK OF EVOLUTION WITHIN HOMO ERECTUS
If evolution were true, claims Lubenow, we would expect change over time within Homo erectus, but we dont get it. Why would we, I may ask? He has heard of punctuated equilibria, but not, apparently, of stasis, an inescapable corollary of the punctuationist model, and well-known to evolutionary theory well before Eldredge and Gould wrote their seminal paper.
THE FATE OF HOMO ERECTUS
Lubenow next brings up the debate over modern human origins: "Out of Africa" ("Noah's Ark", "African Eve", including "Mitochondrial Eve") versus Regional Continuity. Good; at the time I wrote my review of his book, he had not heard of this debate. And he even realises that "Mitochondrial Eve" does not imply that at any time there was just a single female ancestor.
The "Out of Africa" model, he notes, is "politically correct", as it stresses the unity of humanity; it is favoured by the supporters of punctuated equilibria; and there is a hint of catastrophism. The molecular evidence for it has fallen away (well, he says so, anyway). And, he claims, it is completely falsified by the Asian fossil record because a lot of "individuals having a Homo erectus morphology" (he says at least 67) are less than 100,000 years old. (He apologises for having to use "evolutionary dating" here). As evidence for this claim, he cites his book Bones of Contention, but fails to cite my review of it in which I refuted them.
As for the Multiregional Evolution model, the interfertility of all human populations falsifies it. Now, I have argued against the Multiregional model in the past, but interfertility is not an argument. He quotes Rouhani:
Even under ecologically identical conditions which rarely exist in nature, geographically isolated populations will diverge from each other and eventually become reproductively isolated... It seems to me that the multiregional model of modern human origins is therefore theoretically implausible.
- and Cavalli Sforza:
Very large populations have a genetic inertia... It would take a very long time for mutations to move through such a population. I don't see how the multiregional model could work.
Rouhani says that populations would diverge (which they have to only a limited extent); Cavalli-Sforza, that gene-flow would not be sufficient to prevent divergence. Why reproductive isolation happens - whether it is a by product of genetic divergence, or can be selected for - is argued. Lubenow, and Rouhani, I must concur, get it half right.
So is the logic behind the Out-of-Africa model merely that "only Africa is left", as Lubenow says? He quotes Howells:
The persisting features are such that, in Africa, a transition from Homo erectus to Homo sapiens should be accepted, taking place in a region not determined as yet.
This is not just "faith", as Lubenow claims. Howells, in the passage cited, has just finished referring to archaic specimens like Salé, Ndutu, "Broken Hill" (now called Kabwe), Florisbad, and Omo/Kibish. These retain features from earlier fossil types, such as ER 3733 (which he is calling Homo erectus, though I refer it to Homo ergaster), i.e. their "persisting features". The succession of morphologies, getting closer and closer to Homo sapiens over time, is an inescapable feature of the African fossil record.
I am sorry, but carping and sniping are all very well, but even Lubenow - better though he is in many respects than Gish - ignores context and in the end has nothing to offer but minor quibbles. Very comforting to creationists, of course, but it has little enough to do with science.