Six million-year-old human ancestors left clues found in their ear canal that they would one day walk upright, scientists have revealed.
And they believe that climate change around three and a half million years ago might have speeded up this development.
The discovery was made after scientists reconstructed the ear canal of the ancient apes.
The researchers studying the fossilized skulls of Lufengpithecus or ‘Lufeng ape’ were able to draw clues on how and when our pre-human ancestors went from climbing trees to crawling on all fours and, finally, to walking on two legs.
In reconstructing the ear canal of the ape, scientists also found that cooling global temperatures may have been an environmental catalyst which quickened our evolution.
Scientists have long been puzzled as to how humans’ bipedal stance and movement evolved from a quadrupedal ancestor running around on all fours.
Past studies and fossil records have thus far been unable to provide a clear and definitive history of the early evolutionary stages that led to us walking on two legs.
But a new international study, published in the journal Innovation, has finally provided some clues.
Scientists focused on recently discovered evidence from the skulls of the six-million-year-old ape.
In analyzing its bony inner ear region using three-dimensional CT scanning, the researchers found important clues as to the origins of the evolution that saw our ancestors begin walking on two feet.
Yinan Zhang, a doctoral student at the Chinese Academy of Sciences’ Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) and lead author of the study, explained how the inner ears of mammals offer valuable evidence as to how they moved around.
“The semicircular canals, located in the skull between our brains and the external ear, are critical to providing our sense of balance and position when we move, and they provide a fundamental component of our locomotion that most people are probably unaware of,” Mr Zhang said.
“The size and shape of the semicircular canals correlate with how mammals, including apes and humans, move around their environment.
“Using modern imaging technologies, we were able to visualize the internal structure of fossil skulls and study the anatomical details of the semicircular canals to reveal how extinct mammals moved.”
Dr. Terry Harrison, a New York University anthropologist and one of the study’s co-authors, said their findings pointed toward a three-stage evolution in humans which started in the trees and eventually led to how we move today.
“Our study points to a three-step evolution of human bipedalism,” Dr. Harrison said.
“First, the earliest apes moved in the trees in a style that was most similar to aspects of the way that gibbons in Asia do today.
“Second, the last common ancestor of apes and humans was similar in its locomotor repertoire to Lufengpithecus, using a combination of climbing and clambering, forelimb suspension, arboreal bipedalism, and terrestrial quadrupedalism.
“It is from this broad ancestral locomotor repertoire that human bipedalism evolved.”
Though the majority of studies on the evolution of ape movement focus on comparisons of the bones of the limbs, shoulders, pelvis and spine, the diversity of movement behaviors in living apes and the incompleteness of the fossil record have hampered efforts to elucidate humans’ bipedalism origins.
But the skulls of Lufengpithecus – originally discovered in China’s Yunnan Province in the early 1980s – have allowed scientists to address unanswered questions about the evolution of human movement in new ways.
However, the heavy compression and distortion of the skulls obscured the bony ear region and led previous researchers to believe that the delicate semicircular canals were not preserved.
So, to better explore this region, the research team used three-dimensional scanning to illuminate these portions of the skulls and create a virtual reconstruction of the inner ear’s bony canals.
They then compared these scans to those collected from other living and fossil apes and humans from Asia, Europe, and Africa.
IVPP Professor Xijun Ni, who led the project, said: “Our analyses show that early apes shared a locomotor repertoire that was ancestral to human bipedalism.
“It appears that the inner ear provides a unique record of the evolutionary history of ape locomotion that offers an invaluable alternative to the study of the postcranial skeleton.
“Most fossil apes and their inferred ancestors are intermediate in locomotor mode between gibbons and African apes.
“Later, the human lineage diverged from the great apes with the acquisition of bipedalism, as seen in Australopithecus, an early human relative from Africa.”
In studying the rate of evolutionary change in the fossilized apes’ bony labyrinth, the researchers also proposed that climate change may have been an important environmental catalyst in promoting the diversification of movement in apes and humans.
Dr Harrison said: “Cooler global temperatures, associated with the build-up of glacial ice sheets in the northern hemisphere approximately 3.2 million years ago, correspond with an uptick in the rate of change of the bony labyrinth and this may signal a rapid increase in the pace of ape and human loco motor evolution.”
Produced in association with SWNS Talker
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