A 3.3 Million Year Old Baby: A Human Evolutionary Link
By Dr. Rizwana Rahim
Chicago, IL

Last September, two scientific papers published in “Nature”* announcing the discovery of the near-complete fossilized remains of a three-year-old human-like baby girl, who died some 3.3 million years ago, made headlines. The story has prominently featured since in popular science magazine, like New Scientist, Discover, National Geographic (which partly funded the research) and Scientific American (December).
This fossil was spotted in December 2000 by a visitor to the Dikika region of Ethiopia, across the winding Awash River, and unearthed by a team led by an Ethiopian paleoanthropologist, Zeresenay Alemseged, of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Zeresenay saw smooth brow and small canne teeth, among other human features. But it took his team five years to remove the entire fossil buried in sandstone sediments. The Afar depression in the north of Africa’s Great Rift valley has seen for decades many paleontological expeditions by foreign research teams.
This fossil, later christened ‘Selam’ or ‘peace’ in some Ethiopian languages, belongs to the species, Australopithecus afarensis, ancestral to humans, and is perhaps the best and most complete fossil of the species ever found. Main characteristics of this species projecting snout and narrow nasal bones, which can easily distinguish her from another member (Taung child from South Africa) of a closely-related A. afarensis species. Selam is a member of the same as what is nicknamed Lucy, an adult skeleton found in 1974, just 4 kilometers from the Selam site.
Twenty years ago, Lucy was regarded as the oldest human ancestor (an adult) known to science. Selam is at least 100,000 years older than Lucy. These Australopithecines, according to Dr. Alemseged, “a very good transitional species for what was before four million years ago and what came after three million years." This northeastern Ethiopia region is a virtual goldmine of pre-human fossils — some of the highly productive areas are: Gona (Ardipithecus ramidus); Hadar (Ausrathopithecus afarensis); Middle Awash (A. afarensis, A. garhi, Ar. ramidus, Ar. Kadabba); and Dikika (A. afarensis; Selam).
The bones in children are quite fragile and hence, rarely preserved, which is why the near-complete remains of Selam is an extremely rare find. It is possible that the baby died in a flood, rolled into ball and was quickly buried in the sediment, thus protected from further damage and exposure. Selam is now beginning to show secrets of this Australopithecus species and other hominins, i.e., a group that includes all in human line, after it branched off the line of chimpanzees.
Selam has a mixture of features similar to both ape and human. It has virtually the whole skull (which Lucy’s was missing), the entire torso with all her tiny ribs, and crucial parts of the upper and lower limbs, knees (size of a dried pea, but no larger than a macadamia nut) – many bones still in articulation -- several fingers still curled in a grasp, a full set of the milk and un-erupted adult teeth still in the jaw (revealed by CT scans). Her heals are wide, like in human.
One of the delicate bones, rarely preserved, is the hyoid, or tongue, bone, which helps anchor the tongue and the voice box. This suggests air-sacs in the throat, just like in an ape. Hyoid can also show how the voice box is constructed and what sounds can be produced. This, according to Fred Spoor of University College London, another member of the study team, is an “early glimpse of the evolution of the human voice box.” This is the only second hyoid found in a hominin: the first was found in a 60,000 year old Neanderthal. Selam had a small brain (estimated 330 cubic centimeters, or 63-88% of its adult size) when she died, the size being similar to that of a similar-age chimpanzee in which by three, almost 90% of the adult brain-size is formed.
The next oldest skeleton of a juvenile that is comparably intact is the so-called Neanderthal baby, about 50,000 years old.
In most non-human primates and other mammals, the babies begin to be independent after nursing. In Salem, however, there are indications of human-like development, i.e., longer dependency on parents. Zeresenay says, in Selam, "We've captured a moment in time for an individual, but also a moment in the life history of a species."
To her discoverers, Selam’s two shoulder blades look more gorilla-like (facing upward), but others think they are more-human-like. Presence of semi-circular canal system in Selam’s inner ear (for maintaining balance, similar to those found in African Apes) favors an arboreal life, and she may not be as fast or agile as the humans. A walking-climbing combination might fit better for Selam lifestyle, might show whether she and A. afarensis spent their time walking on the ground or like ape, had partly lived in the trees like an ape and led an arboreal life.
A major question for more than two decades has been whether our ancestral species first had large brain and then walked on their two feet (bipedalism), or they first became bipedal and then developed large brains. That was partially settled by Lucy who had a small skull, but walked upright. Then in 1980s rose the question: Whether they also lived in trees (arboreal life), because, apart from clear adaptation in the lower limbs for walking, the upper limbs had a number of primitive traits (curved fingers, e.g.) suggesting an arboreal life.
An interesting transition in a human ancestral hominin species!


Editor: Akhtar M. Faruqui
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