BY LENORE PIPES

In print | Published September 28, 2006

More than 30 years ago and 3.3 million years after she died, paleoanthropologists discovered “Lucy” in the Ethiopian desert, one of the most famous, debated and complete hominin skeletal specimens of the species Australopithecus afarensis. The most remarkable aspect of the discovery, one that transformed views on how we became human, was that Lucy was nowhere near us ancestrally, with a brain the size of an ape. Yet, her remains showed clear evidence that she was bipedal, the fundamental characteristic that distinguishes humans from our closest relatives.

Prior to her discovery, the debate over the mechanisms by which we evolved featured theories in which larger brain size, which was correlated with intelligence at that time, was established long before our innovation to walk upright. The notion was that the anatomical shift in posture carried with it changes in the pelvic structure of females. But Lucy’s skeleton was affirmation that the slight narrowing in the birth canal didn’t affect brain size — not even 1.5 million years later when brain size began to rapidly increase in hominins.

I believe that bipedalism is significant in a different way; it represents the first step towards the evolution of modern humans where it engendered unique human adaptations such as increase in brain size, speech and language acquisition and tool use. Without it, we would not have been able to migrate and dominate the world like we do. Recently, a team led by Zeresenay Alemseged from the famous Max Planck Institute of Evolutionary Anthropology revealed a new A. afarensis fossil that might even outshine Lucy just 2.5 miles south of her resting place. Since the discovery of Lucy, Ethiopia’s unstable political situations had made further excavations in this fossil-rich region difficult.

The circumstances surrounding this new discovery compliments Swarthmore College statistician Steve Wang’s predictive model of future fossil findings in the paleontology community.

The new specimen, Selam — nicknamed “Lucy’s baby” — has been estimated to have been born more than 100,000 years before Lucy and only survived until 3 years of age. Selam is the most complete human ancestral infant ever found, and is arguably the most complete finding in human evolution even though it took Alemseged six years to excavate using dentist tools. Unlike Lucy (whose remains are 40 percent of her full skeleton), Selam has a complete torso, fingers and a foot.

Aside from its unprecedented completeness and its rarity (infant’s bones are usually too fragile to make it to the fossil record), Selam holds clues towards the beginnings of childhood, marking the first evidence of growth and ontogenetic development in its species. To accept that bipedalism came first and brain size came second guarantees that for all hominins proceeding A. afarensis, delivery must have been a medical crisis for the mother and the newborn baby since humans are born vastly more immature than primates. Skulls are not even hardened at the time of delivery, and after that, infancy is faced with numerous hazards such as infanticide or parental neglect.

Universally, humans possess a uniquely prolonged stage of childhood that allows for a slow, steady rate of body growth, but an exponentially rapid rate of brain growth. To me, childhood is an example of a human-specific feature that is characterized by intellectual and social development rather than physical development which is biologically emphasized in our close relatives. If physiological development was stressed and the learning process of childhood was absent, we could imagine an adult-sized 4-year-old in the midst of resource and mate competition — what an alarming thought.

On the other hand, childhood might even be an old tactic that college students use: a ploy to extract parental investment. Above all and more importantly, human childhood maximizes the extent to which learning and complex culture can occur through delayed maturity. Selam will provide insight into fundamental questions that researchers have been attempting to answer when, why and how did this change for prolonged dependence on parents occur?

Among other significant research that can be studied through Selam, Alemseged also managed to recover the hyoid bone, which influences the voice box and later became crucial for developing speech. The only other hyoid that has been recovered in any pre-human ancestor is that in a Neandertal specimen, which is one of the hotly debated features over the species’ capability for speech.

Although I personally believe that one plausible explanation for the disappearance of Neandertals is that they were not capable of communicating as effectively with each other as Homo sapiens. Just imagine a human-like species with a bigger brain but without the ability to talk to each other. Fitness-wise, they wouldn’t last long. Selam’s hyoid is more ape-like (suggesting that A. afarensis was not capable of speech), but it provides one of the only resources to study the evolution of the human voice box.

The 3-year-old child is a mosaic in human evolution bearing the initial costs of what it means to be human, walking upright and having a large brain, but still displaying primitive characteristics. No doubt, the discovery of Selam, like that of Lucy, will raise new questions to debate about in human evolution. In terms of a “missing link”, she has filled a developmental void in the fossil record.

Lenore is a junior. You can reach her at lpipes1@swarthmore.edu.

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