The Pliocene Environment and Hominin Diversity 155addition, a forearm bone from Lucy, which is relatively
shorter than that of an ape, suggests that the upper limb
was lighter and the center of gravity lower in the body
than in apes. Still, the arms of Lucy and other early aus-
tralopithecines are long in proportion to their legs when
compared to the proportions seen in humans.
Though she lived about 150,000 years before her
namesake, “Lucy’s baby,” the discovery from Ethiopia an-
nounced in 2006, will add considerably to our knowledge
about A. afarensis once the analyses are complete.^3 These
fossilized remains of a young child, dated to 3.3 mya, were
discovered in the Dikika area of northern Ethiopia in- Because the remains of this child, thought to have
died in a flash flood, are particularly well preserved, sci-
entists can investigate new aspects of this species’ biology
and behavior. For example, a preserved hyoid bone (lo-
cated in the throat region) will allow scientists to recon-
struct australopithecine patterns of vocalization. While
the lower limbs clearly indicate bipedalism, the specimen’s
scapula and long curved finger bones are more apelike.
The curvature of the fingers and toes and the some-
what elevated position of the shoulder joint seen in adult
specimens indicate that A. afarensis was more adapted to
tree climbing compared to more recent human ancestors.
In the following Original Study, paleoanthropologist John
Hawks discusses the kinds of evidence used to reconstruct
a behavior such as tree climbing in our ancestors.
(^3) Zeresenay, A., et al. (2006). A juvenile early hominin skeleton from
Dikika, Ethiopia. Nature 443, 296–301.
Fossil finds are rare enough, but a well-preserved juvenile specimen
is especially unusual. The skull and skeleton of this young girl are
actually tens of thousands of years older than Lucy, but due to her
incredible preservation, she has been nicknamed “Lucy’s baby.” In
addition to the skull pictured here, this specimen includes a torso,
fingers, and a foot.
© Vilem Bischof/AFP/Getty Images
Original Study
Ankles of the Australopithecines by John Hawks
Recent University of Michigan Ph.D. Jer-
emy DeSilva gets some nice press about
his work demonstrating that fossil homi-
nins didn’t climb like chimpanzees.
“Frankly, I thought I was going to
find that early humans would be quite
capable, but their ankle morphology
was decidedly maladaptive for the kind
of climbing I was seeing in chimps,”
DeSilva told LiveScience. “It kind of
reinvented in my mind what they were
doing and how they could have survived
in an African savannah without the
ability to go up in the trees.”a
This is a good example of the com-
parative method in paleoanthropol-
ogy. We can’t observe the behavior of
extinct species; we can only observethe behavior of their living relatives.
We can observe the anatomy of fos-
sil specimens, but testing hypotheses
about their behavior requires us to
understand the relationship between
anatomy and behavior in living species.
We’ve known about the anatomy of fos-
sil hominid ankles for a long time, but
it’s not so obvious how the anatomical
differences between them and chim-
panzee ankles relates to behavior.
DeSilva studied the tibiae and ankle
bones of early hominins and concludes
“that if hominins included tree climb-
ing as part of their locomotor repertoire,
then they were performing this activity
in a manner decidedly unlike modern
chimpanzees.”DeSilva’s conclusion is straightfor-
ward and easy to illustrate. Chimpanzees
climb vertical tree trunks pretty much
like a logger does. A logger slings a strap
around the trunk and leans back on it.
Friction from the strap holds him up as
he moves his feet upward; spikes on his
boots hold him while he moves the strap.
Of course, chimpanzees don’t have
spikes on their feet, and they don’t
use a strap. Instead, their arms are
long enough to wrap around the trunk,
and they can wedge a foot against the
trunk by flexing their ankle upward—
dorsiflexing it—or grip the trunk by
bending the ankle sideways—inverting
the foot—around it. The paper includes
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