[Catalyst 2016] Final

PHOTOS FROM:
WIKIMEDIA COMMONS
Homo naledi
A New Piece in the Evolutionary Puzzle
By Ethan Wissell
H
uman beings share 96% of their
genomes with chimpanzees,which is
why modern science has accepted
the concept that humans and apes share
a recent common ancestor. 1 However,
our understanding of the transition from
these ancient primates to the bipedal,
tool-wielding species that conquered
the globe is less clear than many realize.
One crucial missing chapter in the
evolutionary story is the origin of our
very own genus, Homo. Scientists believe
that somewhere between two and three
million years ago, the hominid species
Australopithecus afarensis evolved into
the first recognizably human species,
Homo erectus. However, the details of
this genealogical shift have remained a
mystery. In 2013, a discovery made in the
Rising Star cave by two recreational cavers
may have provided revolutionary insight
into this intractable problem.
The Rising Star cave lies 30 miles outside
the city of Johannesburg in northern
South Africa. A popular destination for
spelunkers for the past 50 years, this cave
is well-known and has been extensively
mapped. 2 Two years ago, Steven Tucker
and Rick Hunter dropped into the Rising
Star cave in an effort to discover new
extensions to the cave, with the hope of
finding something more. 2 They found
a tight crevice that was previously
unexplored, which led to a challenging
forty-foot drop through a chute. At the
bottom, Hunter and Tucker came across
scattered bones and fossils in what would
later be named the Dinaledi chamber. 2
Hunter and Tucker consulted with Dr.
Lee Berger, a paleoanthropologist at the
University of Witwatersrand. It was clear
to Dr. Berger that these fossils were not
of modern humans — an ancient hominid
species had been discovered. 2
Within weeks of this discovery, Dr. Berger
assembled a qualified team and set up
camp at the mouth of the Rising Star cave.
In the largest hominid artifact discovery
in Africa, over one thousand bones from
multiple bodies were extracted and
analyzed. 2
As the fossils were being transferred
out of the cave, paleoanthropologists at
the surface worked to piece together a
skeleton. Some aspects of this species’
bone structure were distinctly human, like
the long thumbs, long legs, and arched
feet. 2 Other features, including curved
"these fossils
were not of modern
humans. An ancient
hominid species had
been discovered."
fingers and a flared pelvis, were indicative
of a more primitive animal. 2 A large skull
fragment from above the left eye of
one of the skeletons allowed scientists
to definitively determine this hominid’s
genus.
The Australopithecus skull is characterized
by a large orbital ridge above the eye,
with a deep concavity behind it, leading
to a flatter face with pronounced brows. 3
The skull fragment collected by the team,
however, had a shorter ridge and less of
an indentation above the frontal lobe. 3
This finding led the team to conclude that
they had discovered a new member of
the Homo genus, which Dr. Berger named
Homo naledi. ‘Naledi’ in the Sotho language
means ‘star,’ a reference to the vivid
stalactites emanating from the ceiling of
the Dinaledi chamber. 3
Dr. Berger’s discovery in the Rising Star
cave was an incredible breakthrough, but
finding fossils is only half the battle. The
next step is to find a place for this species
in the million-year narrative of human
evolution we have created.
In accomplishing this feat, a logical place
to start is considering how the fossils of
Homo naledi ended up in their final resting
place. There were no signs of predation,
as no other animal fossils were found
at this location. In addition, these fossils
accumulated gradually, meaning that the
bodies did not all die from a single event.
Dr. Berger postulated that these bodies
were placed there with purpose, but
intentional body disposal is an advanced
social behavior which, up to this point,
has only been exhibited by more evolved
Homo species. The brain size of the
discovered hominids is estimated to be
between 450 and 550 cubic centimeters,
about one third the size of the Homo
sapiens brain and only marginally larger
than that of a chimpanzee. 3 The possibility
of such a small-brained animal engaging in
intentional body disposal challenges ideas
about the cognitive abilities necessary
for such advanced social behavior. Dr.
William Jungers, chair of anatomical
sciences at Stony Brook University, argues
that advanced social intelligence was not
9
CATALYST