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!
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