Australopiths shared several traits with modern apes and humans, and were widespread throughout
Eastern and
Northern Africa by 3.5 million years ago (MYA). The earliest evidence of fundamentally bipedal hominins is a 3.6 MYA
fossil trackway in Laetoli, Tanzania, which bears a remarkable similarity to those of modern humans. The footprints have generally been classified as australopith, as they are the only form of prehuman hominins known to have existed in that region at that time.
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According to the
Chimpanzee Genome Project, the
human–chimpanzee last common ancestor existed about five to six million years ago, assuming a constant rate of mutation. However, hominin species dated to earlier than the date could call this into question.
[38] Sahelanthropus tchadensis, commonly called "
Toumai", is about seven million years old and
Orrorin tugenensis lived at least six million years ago. Since little is known of them, they remain controversial among scientists since the molecular clock in humans has determined that humans and chimpanzees had a genetic split at least a million years later.[
citation needed] One theory suggests that the human and chimpanzee lineages diverged somewhat at first, then some populations interbred around one million years after diverging.
[38]
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