Human Evolution

Fundamentalists and hominin evolution

Despite overwhelming evidence to the contrary, detailed by mainstream archaeologists, geneticists and palaeoanthropologists in thousands of publications, creationist fundamentalists maintain that modern humans do not share a common ancestor with chimpanzees. In the UK, there is a young-earth creationist organisation called Truth in Science, which promotes Intelligent Design creationism. Truth in Science continues to engage in uncritical and deliberately misleading statements about our evolutionary past, and proposing what effectively amounts to a dilution of teaching human biology in school science classrooms.

No member of Truth in Science is actively involved in archaeological or palaeoanthropological research. In addition, they refuse to submit their reviews to scientific journals for peer review and subsequent critique by the relevant scholars. This behaviour should not come as a surprise as they have openly stated, and subsequently tried to hide the fact, that they believe anyone who disagrees with them is a charlatan and must be confronted. Through selective targetting of well supported scientific hypotheses and models, they attempt to portray some as tentative and others as outright incorrect.

Take, for example, the Truth in Science article entitled Ancient ape-like fossil described in Nature on the discovery and subsequent analyses of the young Australopithecus afarensis skeleton, the Dikika juvenile. The article does not categorically deny that man is descended from apes, but the implication is implicit and the wording "designed" to create doubts in the mind of the reader. Instead, lets us look directly at what was actually stated in the relevant journal publications.

Essentially what the Truth in Science author(s) is/are accusing Bernard Wood, one of the world's foremost palaeoanthropologists, of is misinterpreting and subsequently exaggerating the data and findings of the research team. Wood's job, as the commentator, is to place the data and findings within the wider context of existing palaeoanthropological research and debates. I have yet to come across the sorts of exaggerations in Wood's writings and papers that TiS are effectively accusing him of, impinging a well-respected scientist's reputation. This sort of behaviour is unprofessional and unethical, giving lie to their claim they would welcome inaccuracies pointed out for correction.

The Dikika juvenile was found by the Dikika Research Project members in Ethiopia. The sandstone sediment in which the child was found was deposited on a subaerial delta plain; the age of the Sidi Hakoma Member ranges from 3.31 - 3.35 million years. When combined with the lack of pre-weathering of the anatomical remains, these factors indicate that the child was buried in a flood.

The initial anatomical report (Alemseged et al. 2006) is the accumulation of five years of painstaking cleaning and examination. Most of the postcranial remains were covered by sandstone matrix, together with the cranium's midface, left temporal bone and the cranial base.

Analysis of the skeletal elements places the child firmly within the known range for Australopithecus afarensis and distinguish them from modern gorillas and chimpanzees. CT-scans were used to model the age using an African ape model. The resulting 3 years of age would not differ by more than a year and a half if a modern human model had been used instead. Given that A. afarensis is a hominin, the utilisation of an African ape model is a prudent measure for a minimum age.

The tibiae has a sharper anterior border and its muscle attachment orientations resemble that of modern humans. In addition, also like modern humans, the side of the upper part of the shaft is a little concave, becoming convex towards the back. The ape-like scapula, the longer phalanges and the reconstructed environmental settings (woodland with a nearby plain) all combine to reinvigorate investigations into the mobility patterns of A. afarensis. The basis of these investigations will likely be that A. afarensis combined a form of arboreal behaviour with habitual bipedalism, as reflected by the more derived lower body which would have been under variable selection pressures.

As more of the sandstone matrix is removed from the skeletal remains and further analysis is made possible (hopefully including isotope analysis), we expect to see the new models of hominin growth, dietary and evolutionary patterns emerging over the coming years. These will yield valuable insights which can then be tested against the known and future anatomical remains of both A. afarensis and other hominin species.

If you compare this information with that provided by the article on the Truth in Science web site, it is evidence that Truth in Science fail to mention their leading members' affiliation to American young-earth creationist organisations Answers in Genesis and the Biblical Creation Society. Ask yourself too what the impact on your child's likely exam results would be if they repeat the creationist pseudoscience that has been pushed by Truth in Science proponents.

Subsequently, Truth in Science published an article on their website entitled Comparative Genetics and Biochemistry. The anonymous author superficially critiques the genetic arguments for common ancestors, in particular humans and chimpanzees sharing a common ancestor, and concludes, "The patterns of similarity and difference in living organisms are fully consistent with design." What, though, is the good of making sweepingly generalised statements on human genetics without adding in similar misconceptions on anatomy? Such misrepresentations appear on their hominid fossils page: a pretence that the fossil record is too fragmentary and incomplete for any plausible hypotheses to be proposed on hominin ancestry (i.e. homologies are to be explained instead by recourse to "structural and functional contraints"), complete with a complementary creationist side-swipe against particular interpretations of the AL 288-1 skeletal remains (Lucy, the female Australopithecus afarensis)

In disabusing these inaccurate conclusions, lets begin by looking at the the number of hominin fossil remains available for study. For the sake of time, and merely as an illustration, I will summarise Fred Grine's contribution ("Description and preliminary analysis of new hominid craniodental fossils from the Swartkrans Formation") in:

The remains from these main palaeoanthropolgical sites are beautifully described in The Human Fossil Record series, edited by Jeffrey Schwartz and Ian Tattersall. The box below lists the sites first in Africa, Asia and Europe where fossils of the genus Homo have been excavated and analysed.

The palaeoanthropological and archaeological evidence derived from these and numerous earlier australopith localities demonstrate that australopiths and chimpanzees share a geologically recent common ancestor and that Homo sapiens are descendants of the evolutionary branch that began with the divergence of the australopiths.

The anatomical characteristics that link the australopiths to Homo, and show their intermediate form between modern humans and the last common ancestor between humans and chimpanzees, include:

• The canines of the australopiths do not project much further forward in relation to the other teeth than they do in Homo; Australopith canines also show a decrease in sexual size differences over time - the more recent forms are more like the condition of modern humans;
• Tooth enamel progresses to a more Homo-like thickness over time;
• Wear patterns on australopith teeth suggest a "crushing" action, similar to that of Homo;
• The cranial capacity of the australopiths increases to a capacity range approaching that of early Homo;
• The australopith foramen magnum, which allows the spinal cord to connect with the base of the brain, is located more toward the base of the skull than in apes, yet not completely under the skull, as in Homo but excluding the robust australopiths (also known as Paranthropus) where it was just as in Homo; and
• The features of the tibiae (orientation angle, thickness and internal structure) shared by australopiths and Homo reflect the demands placed on their bodies by bipedalism.

The anatomical similarities between chimpanzees and anatomically modern humans (Homo sapiens) can be summarized as follows:

• In both species, the rib cage is broad from side to side and shallow from front to back; the rib cage extends back beyond the vertebral column
• Both have a dorsally-placed scapula and shoulder joints facing outward to the side, giving humans a mobile shoulder joint; a hangover from our arboreal ancestry; and
• The positioning and angle of the humeral shaft and humeral head and other joints in the forelimb are the same in both species.

Table 1 below summaries the similarities and differences between chimpanzees, australopiths and modern humans as a result of millions of years of evolution.

It is also worthwhile noting Bernard Wood and Brian Richmond's (2000) summary of comparative limb morphology: "The substantial differences between the lower limbs of modern humans and apes are largely attributable to the bipedal locomotion of the former. The most striking difference is the great absolute and relative length of modern human lower limbs that increases stride length and thus the speed of bipedal walking. Because the lower limbs support the body during bipedal gait, the acetabulum, femoral head and other lower limb joints are relatively larger in humans. Modern human femora are distinctive in that they show the valgus condition (i.e. they converge towards the knees), thus helping to position the feet closer to the midline."

Interestingly, Lucy (AL 288-1) is one of the smallest individuals from the Hadar collection belonging to Australopithecus afarensis and was an obligate bipedal hominin ancestor. Her skeletal remains are 40% complete (Larson et al. 1998), comprising some 47 out of 206 bones (Johanson & Edgar 2001). Her estimated size is ca. 105 cm and she had a weight of ca. 27 kg. Her femur length is 27 cm, which contrasts with the 40.4 cm femur of AL 333-3. Sexual dimorphism is also present in the upper limb bones: the humerus of AL 137-50 and the ulna of AL 438-1 is roughly 25% greater. Lucy's pelvis is constricted front to back and her sacrum wider compared to present-day women, which indicates a gestation period closer to present-day apes and a brain size at birth comparable to chimpanzees. While Häusler & Schmid (1995) have disputed the attribution of Lucy as a female based on pelvic metric data and shape, Tague and Lovejoy's (1998) subsequent pelvimetric analysis show vital flaws in their argument. With no male pelvis known from the current Australopithecus afarensis collections, the shape of Lucy's pelvis (to a lesser extent) and the magnitude of sexual dimorphism present in the Hadar collection argues strongly in favour of Lucy's female attribution.

In addition, recent reviews of the available anatomical (Shoshani et al. 1996) and genetic evidence (Ruvolo 1995, 1997; Wise et al. 1997) have convincingly re-affirmed yet again the theory that apes and anatomically modern humans share a common ancestry. The DNA sequences of human chromosomes 2 and 4 have been completely analysed and were published in the April 7 (2005) issue of Nature, reinforcing the conclusions reached by previous studies. In essence, the chimp chromosomes 2a and 2b fused to form the human chromosome 2. Previous comparisons between the chimpanzee and human genomes and other known genomes have yielded a gene which appears to be functional only in chimpanzees and humans. This gene is suggested to make a protein in the brain and testicles. Furthermore, geneticists have analysed the differences in the amino acid sequences of protein and in the base sequences of DNA from apes and humans; the results have yielded a divergence time-frame of 5-8 million years ago.

The genetic basis for a LCA (Last Common Ancestor) between chimpanzees and humans is not in dispute amongst mainstream evolutionary geneticists. Before and with the publication of the chimpanzee genome, geneticists have focused on identifying and exploring genetic dissimilarities at a functional level, looking at show the differences affect development, mental maturation, reproductive biology and other aspects of life history. At the same time, the estimated 1%+ difference between humans and chimpanzees have always been known to be based on certain types of genetic analyses. As a consequence, the short summary provided on the Truth in Science news page is disingenious in that it attempts to portray studies, showing a greater differential percentage in select genome components, as having "profound implications for Darwinian evolution"; coming from an organisation which believes the Earth is 6000 years old, it becoems clear their statement attempts to cast a shadow over genetic research demonstrating a LCA between humans and chimpanzees. Our evolution is comprised of multiple steps, some of which would have left their footprint in our genome. Genetic processes such as chromosomal rearrangements and the amplification of transposable elements or endogenous retroviruses most likely have affected the genomes of our ancestors in profound ways that allowed subsequent novel adaptations.

At this point, it is worth pausing to reinforce this information with a pertinent summary provided by the anthropologist Professor Jonathan Marks on pages 39- 40 of his publication What it means to be 98% chimpanzee: Ape, people and their genes:

There is another category of evidence which has been brought to bear on the study of hominin evolution: brain endocasts. The eminent Professor Ralph Holloway has authored and co-authored a number of seminal papers on the subject, some of which are available on his university webpage. His work was brought together in a co-authored massive publication in The Human Fossil Record series. The authors trace the evolution of the hominin brain from Australopithecus afarensis through to anatomically modern humans. Australopithecus afarensis specimens evidence an important reorganisation of the cerebral cortex which is inclined towards the human condition. The environmental and skeletal evidence from their localities is highly suggestive of different behavioural patterns to their gorilla and chimpanzee ancestral counterparts. By this stage, re-organisation of the brain's structure was preceding a relatively large brain expansion (estimates of the ancestral group range from 300 - 400ml; A. afarensis is ca. 385 - 550ml).

These models and predictions are based upon detailed anatomical evidence and do not use any particular religious text either as the starting point or as the given conclusion. I would urge readers of this article to watch the Natural History Museum video of Professor Chris Stringer discussing the early modern human crania from Herto, Ethiopia, to get a visual insight into how the discipline of palaeoanthropology works. Finally, I strongly urge you to pay heed to the wise words of the palaeoanthropologist Professor C. Loring Brace (1983), with which this article ends.

Recommended readings

Alemseged, Z., Spoor, F. Kimbel, W., Bobe, R., Geraads, D., Reed, D. & Wynn, J. 2006. A juvenile early hominin skeleton from Dikika, Ethiopia. Nature 443(21): 296-301

Brace, C.L. 1983. Humans in time and space. In Godfrey, L. (ed.) Scientists confront creationism. London: W.W. Norton & company

Hausler, M. & Schmid, P. 1995. Comparison of the pelves of Sts 14 and AL 288-1: Implications for birth and sexual dimorphism in australopithecines. ''Journal of Human evolution 29: 363-383

Johanson, D. & Edgar, B. 2001. From Lucy to language. London: Cassell Paperbacks

Jungers, W.L. 1988. Relative joint size and hominoid locomotor adaptations with implications for the evolution of hominid bipedalism. In, Strasser, E. & Dagosto, M. (eds.) The Primate Postcranial skeleton: Studies in Adaptation and Evolution, pp. 247-265. London: Academic Press

Larsen, C., Matter, R. & Gebo, D. 1998. Human origins: The fossil record. Illinois: Waveland Press, Inc.

Pilbeam, D. 1996. Genetic and morphological records of the Hominoidea and hominid origins: a synthesis. Molecular Phylogenetics and Evolution 5: 155-168

Richmond, B. & Strait, D. 1999. Knuckle-walking traits retained in the wrists of early hominids. American Journal of Physical Anthropology, Suppl. 28: 232

Shoshani, J. et al. 1996. Primate phylogeny: morphological vs molecular results. Molecular Phylogenetic Evolution 5: 101-153

Tague, R. & Lovejoy, O. 1998. AL 288-1—Lucy or Lucifer: gender confusion in the Pliocene. Journal of Human Evolution 35: 75-94

Tardieu, C. & Trinkaus, E. 1994. Early ontogeny of the human femoral bicondylar angle. American Journal of Physical Anthropology 95: 183-195

Walmsley, T. 1933. The vertical axes of the femur and their relations. A contribution to the study of erect posture. Journal of Anatomy 67: 284-300

Washburn, S.L. 1967. Behaviour and the origin of Man. Proceedings of the Royal Anthropological Institute 3: 21-27

Wise, C. et al. 1997. Comparative Nuclear and Mitochrondrial Genome Diversity in Humans and Chimpanzees. Molecular Biology Evolution 14(7): 707-716

Wood, B. & Richmond, B. 2000. Human evolution: taxonomy and paleobiology. Journal of Anatomy 196: 19-60

Wynn, J. Alemseged, Z., Bobe, R., Geraads, D., Reed, D. & Roman, D. 2006. Geological and palaeontological context of a Pliocene juvenile hominin at Dikika, Ethiopia. Nature 443(21): 332-336