‘Uniquely human’ muscles have been discovered in apes
The presence of certain muscles in bonobos and other apes challenges views that some muscles evolved solely for providing special adaptations of human traits. Image: Shutterstock
Apes also have muscles long-believed to be only present in humans and used for walking on two legs, using complex tools, and sophisticated facial and vocal communication
— By Tania Fitzgeorge-Balfour
Muscles once thought ‘uniquely human’ have been discovered in several ape species, challenging long-held theories on the origin and evolution of human soft tissues. The findings question the anthropocentric view that certain muscles evolved for the sole purpose of providing special adaptations for human traits, such as walking on two legs, tool use, vocal communication and facial expressions. Published in Frontiers in Ecology and Evolution, the study highlights that thorough knowledge of ape anatomy is necessary for a better understanding of human evolution.
“This study contradicts key dogmas about human evolution and our distinct place on the ‘ladder of nature,'” says Rui Diogo, an Associate Professor in the Department of Anatomy at Howard University, Washington, USA. “Our detailed analysis shows that in fact, every muscle that has long-been accepted as ‘uniquely human’ and providing ‘crucial singular functional adaptations’ for our bipedalism, tool use and vocal and facial communications is actually present in the same or similar form in bonobos and other apes, such as common chimpanzees and gorillas.”
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Long-standing evolutionary theories are largely based on the bone structures of prehistoric specimens — and, according to Diogo, also on the idea that humans are necessarily more special and complex than other animals. These theories suggest that certain muscles evolved in humans only, giving us our unique physical characteristics. However, verification of these theories has remained difficult due to scant descriptions of soft tissues in apes, which historically have mainly focused on only a few muscles in the head or limbs of a single specimen.
Diogo explains, “There is an understandable difficulty in finding primate, and particularly ape, specimens to dissect as they are so rare both in the wild and museums.”
To find enough data to complete this research, Diogo compiled all previous information on ape anatomy based on studies with colleague Bernard Wood. He also conducted anatomical research on several bonobos that died of natural causes, together with colleagues at the University of Antwerp under the Bonobo Morphology Initiative 2016 — looking for the presence of seven different muscles thought to have evolved only in our species.
Diogo discovered that these seven muscles were present in apes in a similar or even exact form. For example the fibularis tertius muscle, said to be uniquely associated with human bipedalism (walking on two legs), was present in half the examined bonobos. Similarly, both the laryngeal muscle arytenoideus obliquus and the facial muscle risorius — thought to have evolved for our uniquely sophisticated vocal and facial communication, respectively — were present in at least some chimpanzees and/or gorillas.
These findings open crucial new directions for research and question our understanding of human evolution. “The picture emerging from this research is that the origin and evolution of human soft-tissue is clearly more complex — and not as exceptional — as first thought,” says Diogo.
“We need a more thorough examination of why these muscles are present in apes and, in some cases, in just part of a population within a certain species,” he says. “Are these muscles essential for the apes that have them, as adaptationist evolutionary scientists would argue? Or are they evolutionary neutral features related to how their bodies develop, or simply by-products of other features?”
He concludes, “Most theories of human evolution give the impression that humans are markedly distinct from apes anatomically, but these are unverifiable ‘just-so stories’. The real evidence shows we are not so different overall. This study highlights that a thorough knowledge of ape anatomy is necessary for a better understanding of our own bodies and evolutionary history.”
Illustration showing the striking similarities between the head muscles of common chimpanzees, bonobos and humans: the very rare exceptions are those shown in colors and with text. Image source: Rui Diogo
Original article: First Detailed Anatomical Study of Bonobos Reveals Intra-Specific Variations and Exposes Just-So Stories of Human Evolution, Bipedalism, and Tool Use
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Can biologists please stop referring to the “ladder of nature” in the twenty-first century? This shouldn’t need reminding.
Thanks.
It is puzzling to me that some people find the tiny differences proposed to exist only in humans so important sa much larger differences occur commonly throughout the animal kingdom. The amazing fact to me is that so many animals (e.g. vertebrates) share such a vast wealth of commonality in anatomy and development, and much more in living chemistry.
wonderful nature, its evolution is how it has to be, not as we would like it to be
Great discovery, thanks, professor Rui Diogo. It’s often assumed that humans evolved from apes, but in fact humans, chimps & bonobos evolved from the same creature that lived some 5 mill.yrs ago, and that probably already had a mixture of human, chimp, bonobo & unique features, IOW, we didn’t evolve from “apes”, but from early hominoids with a lifestyle that no longer exists, google “ape and human evolution 2018 biology vs anthropocentirsm”.