A comparison of ancient and contemporary footprints reveals that our
ancestors were strolling much like we do some 3.6 million years ago, a time
when they were still quite comfortable spending time in trees, according to
a study which will be published in the March 22 issue of the journal PLoS
So rather than quibbling over badly crushed?and often missing?fossil bones,
the researchers behind the new study turned much of their focus back to the
famous Laetoli footprints, which were discovered more than 30 years ago in
what is now Tanzania. Likely left by Australopithecus afarensis, the same
species as "Lucy," these prints show an upright gait, but it has remained
controversial just how fluid and modern this creature's walk would have
"Based on previous analyses of the skeletons of Australopithecus afarensis,
we expected that the Laetoli footprints would resemble those of someone
walking with a bent knee, bent hip gait typical of chimpanzees, and not the
striding gait normally used by modern humans," David Raichlen, an assistant
professor in the Department of Anthropology at the University of Arizona in
Tuscon and lead author on the study, said in a prepared statement.
To test this assertion, Raichlen and his colleagues created a sandy test bed
for contemporary subjects to walk across?both normally and then in a bent,
chimpanzee-like manner. The researchers used a laser scaner to construct 3-D
models of all of the footprints to compare with the Laetoli tracks.
"To our surprise, the Laetoli footprints fall completely within the range of
normal human footprints," Raichen said. The upright, modern walkers' prints
had heal and toe-print depths that were relatively equal, as the Laetoli
prints do, but those locomoting more like chimpanzees?as ancient humans have
been proposed to have done?produced toe prints that were much deeper and did
not match the Laetoli patterns.
"This more human-like form of walking is incredibly energetically efficient,
suggesting that reduced energy costs were very important in the evolution of
bipedalism," Raichlen said.