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Transcript

THE EVOLUTION

OF HUMAN BIPEDALISM

BIPEDALISM

"Walking upright on two legs is the trait that defines the hominid lineage: Bipedalism separated the first hominids from the rest of the four-legged apes." - Erin Wayman, Smithsonian Magazine

According to Merriam Webster, 'Bipedalism' is defined as "the condition of having two feet or of using only two feet for locomotion."

"The oldest evidence for walking on two legs comes from one of the earliest humans known, Sahelanthropus. Walking upright may have helped this species survive in the diverse habitats near where it lived—including forests and grasslands." - Smithsonian Natural Museum of History

Adrian Smith

Sahelanthropus

7-6 MILLION YEARS AGO

"Few specimens of the Sahelanthropus are known, other than the partial skull nicknamed Toumaï. the Sahelanthropus has been often described as 'Possibly Bipedal' and represents the earliest possible example of bipedalism among our ancestors. From at least 6 to 3 million years ago, early humans combined apelike and humanlike ways of moving around. Fossil bones found record a gradual transition from climbing trees to walking upright on a regular basis."

SOURCES

All facts/information gathered using data from the Smithsonian Museum of Natural History

http://www.smithsonianmag.com/science-nature/becoming-human-the-evolution-of-walking-upright-13837658/

"The teeth, brow ridges, and facial structure differ markedly from those found in Homo sapiens. Cranial features show a flatter face, u-shaped dental arcade, small canines, an anterior foramen magnum, and heavy brow ridges. No postcranial remains have been recovered. The only known skull suffered a large amount of distortion during the time of fossilisation and discovery, as the cranium is dorsoventrally flattened, and the right side is depressed..."

http://humanorigins.si.edu/evidence/human-fossils/species/sahelanthropus-tchadensis

ARTIST REPRESENTATION

http://humanorigins.si.edu/evidence/human-fossils/species/orrorin-tugenensis

LEG SUPPORT

http://humanorigins.si.edu/evidence/human-fossils/species/australopithecus-anamensis

Orrorin Tugenensis

http://humanorigins.si.edu/evidence/human-fossils/species/australopithecus-africanus

6.2-5.8 MILLION YEARS AGO

http://humanorigins.si.edu/evidence/human-fossils/species/homo-erectus

Fossil records of the Orrorin Tugenensis indicate that the primate may have walked on two legs. Such records show that the upper part of the thigh bone (femur) is similar in size to those of other large apes, but the angled part more closely resembles that of modern humans. It formed a strong bridge with the hip to support the body’s weight, suggesting Orrorin tugenensis walked upright.

Artist Representation

STRONG KNEE

Australopithecus Anamensis

4.1 MILLION YEARS AGO

Australopithecus anamensis has a combination of traits found in both apes and humans. The upper end of the tibia (shin bone) shows an expanded area of bone and a human-like orientation of the ankle joint, indicative of regular bipedal walking (support of body weight on one leg at the time). Long forearms and features of the wrist bones suggest these individuals probably climbed trees as well.

The size and broad shape of the hip bones of Homo erectus are similar to a modern human’s, showing that this early human species had given up climbing for walking.

HIP SUPPORT

1.95 MILLION YEARS AGO

FULLY BIPEDAL

The pelvis and thigh bones (outline to right) of Homo erectus are similar to modern humans, and show that this early human was able to walk long distances. That ability was a big advantage during this time period. East Africa’s environments were fluctuating widely between moist and dry, and open grasslands were beginning to spread.

1.9 MILLION YEARS AGO

The long thigh bones of Homo erectus enabled its owner to take long strides and therefore to walk farther and faster than earlier humans.

LONG LEG

1.89 MILLION YEARS AGO

CURVED SPINE

Australopithecus Africanus

Homo Erectus Representation

2.5 MILLION YEARS AGO

The curve of your lower back absorbs shock when you walk. It is uniquely human. You can see a similar curve in the spine of this early human, Australopithecus Africanus, who walked upright in a way very similar to modern humans.

"Early African Homo erectus fossils (sometimes called Homo ergaster) are the oldest known early humans to have possessed modern human-like body proportions with relatively elongated legs and shorter arms compared to the size of the torso. These features are considered adaptations to a life lived on the ground, indicating the loss of earlier tree-climbing adaptations, with the ability to walk and possibly run long distances. Compared with earlier fossil humans, note the expanded braincase relative to the size of the face. The most complete fossil individual of this species is known as the ‘Turkana Boy’ – a well-preserved skeleton (though minus almost all the hand and foot bones), dated around 1.6 million years old. Microscopic study of the teeth indicates that he grew up at a growth rate similar to that of a great ape. There is fossil evidence that this species cared for old and weak individuals. The appearance of Homo erectus in the fossil record is often associated with the earliest handaxes, the first major innovation in stone tool technology."

"Au. africanus was anatomically similar to Au. afarensis, with a combination of human-like and ape-like features. Compared to Au. afarensis, Au. africanus had a rounder cranium housing a larger brain and smaller teeth, but it also had some ape-like features including relatively long arms and a strongly sloping face that juts out from underneath the braincase with a pronounced jaw. Like Au. afarensis, the pelvis, femur (upper leg), and foot bones of Au. africanus indicate that it walked bipedally, but its shoulder and hand bones indicate they were also adapted for climbing."

Silhouette of Homo Erectus Skeletal Structure

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