Humans and our closest existing relatives, the apes, display an astonishing diversity of ways to move, extending from bipedal walking on two legs to tree climbing and quadrupedal walking on all fours.
Although scientists have long been fascinated by the question of how humans’ bipedal posture and movement progressed from a quadrupedal ancestor, neither historical studies nor fossil archives have permitted the creation of a distinct and conclusive history of the early evolutionary stages that directed to human bipedalism.
However, new research, which centers on newly exposed evidence from skulls of a 6-million-year-old fossil ape, Lufengpithecus, offers significant evidence about the roots of bipedal locomotion courtesy of an innovative method: examining its bony inner ear region utilizing three-dimensional CT-scanning.
The semicircular canals, situated in the skull between our brains and the external ear, are critical to providing our sense of stability and position when we move, and they deliver an essential component of our motion that most individuals are possibly oblivious of, explains Yinan Zhang, a doctoral student at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences (IVPP) and the principal author of the paper, which can be found in the journal the Innovation. The size and form of the crescent canals relate to how mammals, as well as apes and humans, move about their setting. Using modern imaging technologies, we were able to imagine the internal assembly of fossil skulls and study the structural details of the semicircular canals to disclose how extinct mammals moved.
The study directs to a three-step growth of human bipedalism, adds Terry Harrison, a New York University anthropologist and one of the co-authors. Primarily, the most primitive apes moved in the trees in a manner that was most comparable to features of the way that gibbons in Asia do currently. Additionally, the last mutual ancestor of apes and humans was alike in its locomotor range to Lufengpithecus, using a combination of climbing and clambering, forelimb suspension, arboreal bipedalism, and terrestrial quadrupedalism. It is from this comprehensive ancestral locomotor selection that human bipedalism evolved.
Most research on the evolution of ape locomotion has focused on comparisons of the bones of the limbs, shoulders, spine, and pelvis and the method they are related to the diverse types of locomotor behaviors perceived in living apes and humans. However, the assortment of locomotor behaviors in living apes and the incompleteness of the fossil archive have hampered the creation of a clear picture of human bipedalism’s ancestries.
The skulls of Lufengpithecus—initially revealed in China’s Yunnan Province in the early 1980s—have allowed scientists to address, in new ways, unanswered questions about the development of locomotion. However, the substantial compression and distortion of the skulls concealed the bony ear region and led former scientists to believe that the fragile semicircular canals were not preserved.
To further explore this region, Zhang, Ni, and Harrison, together with other scientists at IVPP and the Yunnan Institute of Cultural Relics and Archaeology (YICRA), utilized three-dimensional scanning technologies to highlight these portions of the skulls to generate a simulated reconstruction of the inner ear’s bony canals. They then likened these scans to those sampled from other living and fossil apes and humans from Asia, Africa, and Europe.
The investigation shows that early ape locomotor collection was ancestral to human bipedalism, describes IVPP Professor Xijun Ni, who originated the project. It seems that the inner ear offers a unique record of the evolutionary history of ape locomotion that suggests a vital alternative to the study of the postcranial skeleton.
Most fossil apes and their indirect ancestors are intermediate in locomotor style between gibbons and African apes, adds Ni. Later, the human ancestry diverged from the great apes with the attainment of bipedalism, as seen in Australopithecus, an early human relative from Africa.
By reviewing the rate of evolutionary alteration in the bony labyrinth, the universal team proposed that climate variation may have been a significant environmental catalyst in encouraging the locomotor modification of apes and humans.
Cooler global temperatures, related to the build-up of glacial ice sheets in the northern hemisphere roughly 3.2 million years ago, correspond with an uptick in the degree of change of the bony labyrinth and this may signal a rapid upsurge in the pace of ape and human locomotor development, informs Harrison.
