In Search of the Missing Link

The missing link is a term that is popularly bantered in popular culture, but if you think about it, do you really know what the missing link is?  What it symbolizes?  Its importance to anthropology?  Today's blog post explores the concept of the missing link and potential candidates for this famous yet elusive entity.

The Missing Link (www.anticlothes.com)

The term "missing link" was coined in the early 1900s and describes a transitional hominid specimen that ideally blends features of nonhuman primates and humans and acts as the common ancestor among modern humans and apes, thereby demonstrating where the evolutionary branches between the two groups occurred.  The term was originally associated with the discovery of a "fossil" find known as Piltdown Man.  Piltdown Man was believed to be a Paleolithic hominid skeleton with features of both modern apes and humans, leading to the "missing link" conclusion, but it was eventually discovered that Piltdown Man was a fraud, created out of prejudice, jealousy, and European pride.  

Despite this fraud, the concept of the "missing link" continues.  While much is known about nonhuman primate and human evolutionary paths, there remains the mystery of who the common ancestor between modern apes and humans may be.  Paleoanthropological scholars have made progress toward this mystery, establishing that the most likely defining trait between the two groups would be skeletal evidence of bipedality (the ability to walk on two legs), and several candidates have been identified, including Ardipithecus, Orrorin, and Sahelanthropus. 

Ardipithecus: 

Ardipithecus ramidus  (www.wired.com)

Ardipithecus is one of the earliest known fossil genera, and the first species discovered was that of ramidus in Ethiopia in 1992 and 1993.  A total of 17 fossil fragments making up arms, the base of the skull, child’s mandible, as well as some teeth were found and they were diagnostically dissimilar from any other fossilized remains found to that point, warranting its own genus.  Ardipithecus ramidus (root of the ground ape) was the name used to describe these fossil finds, and they are the earliest discovered hominid ancestor, dating to 4.4 million years ago (mya).  These fossil finds were followed up a year later (in 1994) by more discoveries in Ethiopia.  This time around a total of 90 fragments representing a pelvis, leg, ankle, and foot, which substantiated the previous finds and solidified the place of Ardipithecus ramidus.  

This species is considered part of the Hominidae family because of the forward placement of the foramen magnum, teeth looking  slightly more human than ape, and changes to the elbow, but  this species  remains very ape like in several features, particularly enlarged canine teeth.  Plus, the only evidence of this species being bipedal is evidence of the location of the foramen magnum, and while there is fossil evidence of pelvis and legs, more fossilized evidence is necessary to guarantee without a shadow of a doubt that these species were actually completely bipedal and that the location of the foramen magnum was a true intermediary feature between apes and humans.  Without this defining evidence, some scholars are loathe to classify this species as the "missing link". 

Ardipithecus kadabba was discovered five years later, also in Ethiopia, and to date fossilized remains representing at least five specimens have been recovered.  This species dates to approximately 5.6 to 5.8 mya and is differentiated from the later ramidus by its teeth, which are considered more ape-like.  The only feature that suggests that this species was bipedal was one toe bone, which is not very strong evidence to that effect or being the "missing link".

Orrorin:

Orrorin tugenensis (http://www.smashinglists.com/10-human-evolutional-ancestors/)

Another discovery  at the site of Tugen Hills in Kenya of femurs (upper leg bones), teeth, and portion of the mandible (jaw) that date from 5.6 to 6.2 mya.  The scholars who made this discovery, dubbed Orrorin tugenensis, claim that the morphological  features on the femurs are evidence of bipedal walking, which if true would date this adaptation to 2 million years earlier than originally believed.   But other scholars question if this species belongs in the Hominid lineage, leaving this species and its "missing link" status in question.

Sahelanthropus:

Sahelanthropus tchadensis (http://www.smashinglists.com/10-human-evolutional-ancestors/)

Another species, Sahelanthropus tchadensis, is also believed to be a possible hominid ancestor by some scholars and dates between 7 to 6 mya.  This species was discovered in Chad and consisted of a cranium, jaw fragment, and several teeth.  Several of the cranial features are considered primate-like, but there are some key features that scholars claim to be more human like: small canines, reduced prognathism, continuous brow ridge.  The discovers claim that this species is evidence of the "missing link" between humans and nonhuman primates,  but others claim that the species is more ape than human and therefore in the ape lineage. 

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In conclusion, there remains no definitive evidence that fully supports the discovery of the "missing link" thus far.  This does not mean that the "missing link" did not exist as there is substantial evidence both before and after the spot where the "missing link" would exist that suggests its existence.  The mystery remains and continues to drive the passions and interests of paleoanthropologists.  Who knows-perhaps the discovery of the "missing link" will happen today.  New discoveries are occurring daily.

References:

http://humanorigins.si.edu/evidence/human-fossils/species/orrorin-tugenensis

Feder, Kenneth and Park M. Human Antiquity: An Introduction to Physical Anthropology and Archeology, McGraw-Hill.