Humans belong to the taxonomic family of hominids (or Hominidae) together with chimpanzees, gorillas and orangutans. In fact, chimpanzees and humans belong to the same subfamily tribe (Hominini) and have gradually split apart over a period of 4 million years. Bipedalism (moving on two legs) was a major milestone in hominid evolution. Why or how did bipedalism evolve?
Bipedalism and Hominid Evolution
When the hominids of the Hominini tribe started walking on two legs their world changed. There are many theories as to why or how bipedalism evolved. The different hypotheses focus on feeding, behavioral and climatic conditions that made bipedalism possible. An overview of these theories is presented in Roger Lewin's Human Evolution (Blackwell, 2005). Reasons for this major evolutionary milestone include:
- food access and provisioning (standing on two legs to gather food)
- behavioral changes (vigilance against predators; monogamy)
- energy conservation (bipedalism facilitates body heat dissipation)
- climate change that brought about the decrease of wooded habitats.
Indeed bipedalism was a major step in hominid evolution for it gave early man increased mobility freeing his hands for other uses (manipulation). It also improved early man survival and detection of food resources (raised head improved danger detection and made for more efficient hunting or scavenging). Physical differences between men and women are also seen as a result of bipedalism. Fossil footprints are a "precious window" as to how Homo erectus walked.
What are Fossil Footprints?
Tracks made by animals or hominids are preserved by a combination of events. The process is described in Stephen Tomkins, The Origins of Humankind (Cambridge U. Press, 1998): A volcano erupts covering the landscape with lava ash; shorty after, lava ash is turned into cement-like ash by rain; birds and mammals mark it with their footprints; more ash falls from the volcano sealing the footprints. After millions of years erosion uncovers the prints. The greatest discovery in the history of hominid evolution are the Laetoli fossil footprints found by the team of Mary Leakey in Tanzania in 1976.
Fossil Footprints and Bipedalism
The Laetoli fossil footprints, a major discovery for the history of hominid evolution and bipedalism, are the oldest hominid tracks. They are at least 3.6 million years old and the earliest evidence for bipedal walking. They come from a hominid, perhaps a female carrying an infant, whose body structure is very similar to a modern human's.
"Between 1.8 and 1.5 million years ago, Homo erectus evolved into an ancestor very different to anything that came before", says Matthew Bennet, whose team discovered the second oldest hominini footprints known after Laetoli. New Scientist's Robert Adler ("Fossil footprints reveal our modern walk in the making") reported on 26 February 2009 about Benett's team discovery in the Turkana basin, Kenya: the fossil footprints found were made between 1.53 and 1.51 million years ago by Homo erectus and provided compelling evidence of bipedalism of the early man.
The footprints of these hominids have a clear heel, a pronounced arch and alignment of the big toe with the other toes. They are more recent than Laetoli and point to hominids with a modern stride. The Homo erectus who left this fossil footprints had greater potential for movement to different habitats, for more effective scavenging and for increased meat consumption.
As Paleoanthropologist, W. Jungers told New Scientist "the emergence of our own genus, Homo, is linked to the adaptive shift revealed by these fossilized footprints".
Related Articles on Hominids
Fossil Skeleton and Human Evolution in the Neanderthal Museum
Neanderthal Diet or Cavemen Eating Habits
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