There has been a recent furor in the paleontology and anthropology circles this month, which was really started last spring. In the latest edition of Science (behind a paywall, sorry! Students you can probably access it via your school’s library), five reports have been published on fossil remains discovered last April in South Africa that purport to be humanity’s current “missing link”. I emphasize current for a reason which I will return to later, it is a prescient point. But let us discover this new ancestor!
New data has been published (2011) about (2011) Australopithecus sediba (2010). These two new fossils of a female and a juvenile australopith have now pushed back the ape-human common ancestor by about one to two million years. This is simply fantastic news because it gives us a better look at and understanding of just how we humans evolved from quadrupeds to bipeds with radically different-but-similar morphologies and what that really means historically. The remains are described as having extremely well understood Australopithecine skeletal types while somehow having radically “modern” features in bone formation. Both skulls are very much ape-like but also contain evolving plates and structures to support changing musculature and organs; the brows are very prominent like those of other australopithecines and early Homo species, the orbits (eye sockets) are still very large, the zygomatic process (cheek bones where mandibular muscles and ligaments attach) lies closer to the supraorbital ridge (brow), more convex maxilla (upper jaw plates), low sloping frontal plate, while the parietal (top) and occipital (rear) skull plates are clearly becoming enlarged to support a growing brain case and weight. The foot of Au. sediba is described by Lee Berger, discoverer of the remains, as “a heel bone that’s as primitive as a chimpanzee, attached to the ankle bone that’s as evolved as ours is.” Just taking the evolved ankle and skull plates as evidence, the fossils clearly demonstrate an evolution in typical ape locomotion from quadrupedal 99% of the time to splitting movement between upright and knuckle-walking. I remember reading about the discovery of Au. sediba last year and was utterly entranced by what was purported to be found: a better missing link than Lucy! There is little doubt that in the next few years, our ancestral tree will undergo another rewriting to add this newest member and hundreds of thousands of words will be used to elucidate us as to how these australopithecines lived. I am very anxious to get my hands on those newly published papers, this stuff is absolutely fascinating.
But this all leads to one problem, the issue of the newly termed current missing link. Before I even begin to rant, I will preface it all with this:
I understand the sole usage of terminology such as missing link. It is needed to garner enough attention to this information, both in academia and the general public at large, it serves no other purpose than to generate headlines. What’s more interesting to read, “newly discovered ape-human ancestor” or “newly discovered remains may be missing link to apes”? Yeah, it is not the first choice.
The phrase “missing link” itself is a Victorian holdover when the theory of evolution was new and fresh and barely fleshed out. Everyone, self-respecting scientist or not, figured there were definitive intermediate functionary forms for everything: fish, plants, humans, horses, whales, you name it. Whenever something was found to resemble one species and another, it was deemed to be the “missing link” between species A and species B since it would contain shared morphologies. The etymology of the phrase itself is worthy of a book, but suffice it to say it is simply a linguistic shortcut to mean “new discovery that fills in the gaps between A and B”. You can look at any biological niche and find claims of missing links being discovered every so often and this is where science has to take a backseat to public interest. Good paleontologists and anthropologists know that there is no such thing as a missing link but the public at large, being uneducated and not a scientist, does not understand this concept for the most part. Thanks to less-than-adequate education on evolution and how it occurs is the main contributor to this, sprinkle in social mores about how being a scientist (of nearly any kind) is simply “uncool”.
There are two camps in social science about using the phrase “missing link” in regards to evolution: nothing is missing, we just have not found it yet, and everything is a missing link because of evolution. The great thing is both say the exact same thing with different words, but the perception of what is said is the most important thing. Let’s tackle each one.
Nothing is missing, it just has not been found yet
Most of the anthropologists that I know and follow fall into this camp and it is the one I most identify with because, to me, it makes the most logical sense. However, it is also the viewpoint that can attract the most negative commentary because of fallibility and the unknown. If we haven’t found it, how do we know it is not missing? And this is where understanding evolution comes into play as we as scientists can see and express changes that occurred over hundreds of generations and thousands of years to take an organism from point A to point B. In the case of human evolution, scientists have constructed a cogent ancestral history dating back to 7 million years ago starting with S. tchadensis all the way through H. sapiens sapiens (us!). This history shows the gradual development from mainly quadrupedal locomotion to solely bipedal locomotion and relocation of the foramen magnum from the rear quarter of the skull to its current position under the medial base of the skull, and all the changes in between. This is all demonstrable through biological morphology comparisons of structures. Hell, we can even illustrate the similarities of the whale wrist — did you know whales even had wrists?! — and the human wrist, it’s incredible.
Thanks to evolution, everything is a missing link!
By looking at each human ancestor as a single entity between apes and modern humans, we can identify each one as a missing link. This is because scientists can point to various changes that began to emerge via evolution in ancestors as peak or emergence events. For example, fossils show the evolution of locomotion by pointing to the foramen magnum. As we began to walk upright more and more, the foramen magnum proceeded to move from a distal position to its current medial position. This can be seen as the link between how humans can habitually move around bipedally with the ability to go on all fours, whereas our ape cousins ably do the reverse; this would be a peak event. When you view changes in terms of strict comparison, everything is missing since it’s being purposefully left out but the change from species A to species B can be observed on a one-to-one comparison basis.
The discovery and subsequent analysis of A. sediba is amazing, the more insight on how we evolved gives us a clearer vision of who we are as a species. Now that the first studies of the remains have been published, it will get even more exciting once more anthropologists get their (gloved) hands on the bones or bone molds to conduct things like modality studies and physiological reconstructions. Since one set of remains was what seems to be an adult female, it would be an interesting study to explore sexual dimorphism to hypothesize what an adult male A. sediba would look like! While it is just being called a missing link, these fossils are an important branch of the human family tree that only serves to enrich science’s understanding of ourselves and vertebrates at large.