Evolution of Bipedalism
Bipedalism - Why humans no longer live in the trees?
A brief introduction: The human species is unique in the way we move. Our ability to walk upright on two legs, known as bipedalism, was a huge evolutionary change for our species.
Purpose statement: The purpose of this blog is to discuss why bipedalism developed. There are many hypotheses that have been proposed to explain why today’s humans walk upright.
Background: Our skeleton
The Homo sapien skeleton supports bipedalism. Today our bones are structured so that we can walk upright. Our broad human pelvis, our S shaped spine and the position of the foramen magnum (a large hole in our skull) are all anatomical features that allow us to stand upright and walk great distances.
https://images.app.goo.gl/c6Si61ZT2qf5nyoh6
https://images.app.goo.gl/taL1f5AyaurNEdqb7
Discoveries that proved our ancestors were bipedal: Lucy, the Laetoli Footprints, and Ardi…
Lucy In 1974, paleontologist Donald C. Johanson discovered a 3.2 million-year old fossil skeleton in Hadar, Ethiopia. “Lucy” as it was called showed traits of bipedalism in its skeleton form.
https://images.app.goo.gl/axD62vHxAAkmHRbp6
The Laetoli Footprints
The Laetoli Footprints was the second discovery that documented the early evolution of bipedalism. In 1978, a team of paleontologists lead by Mary Leakey discovered a set of footprints in Laetoli,Tanzania dating back to 3.6 million years ago.The footprints left in wet volcanic ash were made by two humans walking upright side by side.
Credit JOHN READER / SCIENCE PHOTO LIBRARY
“Caption Trail of hominid footprints fossilized in volcanic ash. This 70 metre trail was found by Mary Leakey's expedition at Laetoli, Tanzania in 1978. It dates from 3.6 million years & shows that hominids had acquired the upright, bipedal, free- striding gait of modern man by this date. The trail probably belongs to Australopithecus afarensis & dates from 3.7 to 3.0 million years ago. The footprints show a well developed arch to the foot & no divergence of the big toe. They are of two adults with possibly a third set belonging to a child who walked in the footsteps of one of the adults.”
https://www.sciencephoto.com/media/170821/view/trail-of-laetoli-footprints-
Ardi ! “The Earliest Hominid Remains”
In 2009 important research was completed on fossils remains found during 1990s in Ethiopia. The remains were reconstructed to show a female human like fossil skeleton that dates back to 4.4 million years ago. The skeleton of “Ardi”, short for Ardipithecus ramidus, indicated that she walked up right.
https://images.app.goo.gl/5CXXmtTzVcouVQFX7
Theories explaining the evolution of bipedalism…
Scientists are not sure exactly why our ancestors became bipedal. There are many explanations as to why we became bipedal.
Charles Darwin theory - An original theory first proposed by Darwin suggested that our ancestors became bipedal because walking upright freed the hands to make tools. (This theory has been somewhat discredited since fossil records indicate that bipedalism existed before the occurrence of tool making.)
Savannah theory – This theory suggests that due to climate changing from African forests to open savannah grasslands our ancestors could no longer get their food from the forests and had to travel greater distances to nourish themselves.
The threat model – In line with the Savannah theory, this theory offers that our ancestors had to stand upright to watch over the tall grasses of the savannah to watch out for predators.
Savannah theory - Did the humans evolve on the Savannah? NPR
Postural feeding (reaching for food/balance)- Another explanation for bipedalism is that it was brought about as a feeding posture; early humans stood upright in the trees to reach for food or stood on the ground to reach for food in the trees
Postural feeding
https://images.app.goo.gl/8de9y9djziJJgS6h8
Conserving energy- Bipedalism conserves energy is another hypothesis. By walking upright man is less exposed to the sun’s rays, the body is further away from the hot ground and more exposed to the wind.
Conserving energy
https://images.app.goo.gl/pTRYP9u2djE7wRFx6
Provisioning model (food-gathering/monogamy)- this theory suggests that standing upright allowed males to gather food for females and as a result females would mate only with the males that provided them food.
Question # 1: Why did we become bipedal? Among the 6 theories proposed above (Charles Darwin theory, Savannah theory, Threat model, Postural Feeding, Conserving energy, Provisioning model), which one makes the most sense to you? Is there one reason why we walk upright today? Or is the likely explanation as to why we walk on two feet today a combination of various theories?
Question #2: Thanks to bipedalism, humans have become a dominant species. Without bipedalism, we would still be living in the trees! What advances have we made as humans because of bipedalism?
Hey Natalie,
ReplyDeleteNice topic, I think it's awesome you picked something more narrow as a subject, as it speaks a lot about the research done. I like the section you included with the different theories about bipedalism, as it reflects the uncertain nature of the field of anthropology. I think the fact that there are many theories out there and they all have merit is interesting. Nice job!