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Why aren't humans 'knuckle-walkers?'


Researchers at Case Western Reserve University have cracked the evolutionary mystery of why chimpanzees and gorillas walk on their knuckles: The short explanation is that these African apes climb trees and they are mobile on the ground.

Why aren't humans 'knuckle-walkers?'
Credit: Case Western Reserve University
Their bodies—more specifically, their hands—represent a compromise adaptation allowing both forms of travel.

That’s according to Bruce Latimer, professor of anthropology, anatomy and cognitive science and director of the Center for Human Origins, who was one of the study’s authors. Their work was published in The Anatomical Record.

Latimer said much of the research ties anatomy with its relationship to Newton’s laws of motion: For every action, there is an equal and opposite reaction.

“When you walk, there’s a reaction from the ground pushing up,” he said. “Chimps and gorillas are large bodied animals and, as a consequence, they have trouble dissipating all that ground reaction energy.”

This is especially true given the anatomical adaptations they have for climbing, Latimer said.

“In running humans, these reaction forces, can be multiples of body weight on a single supporting foot,” he said. “That’s why we have a uniquely human adaptation the arch in our foot—it’s a shock absorber.”

This also why the old saw rings true that people with flat feet can’t join the infantry, Latimer said. “Without the shock absorbing properties of the arch, long marches would result in damage to the bones of the foot and ankle.”

In chimps and gorillas, climbing adaptations don’t allow them to walk upright. They have long arms, short legs, stiff backs and cone shaped torsos.

Their triangle-shaped torsos allows for better rotation at the shoulder which also serves as a shock dissipater during knuckle walking, according to the research. In addition, chimps and gorillas also utilize their forearm muscles for climbing and for impact absorption when on the ground.

“Clearly, when humans stood up, we completely forfeited the use of our upper limbs for locomotion,” Latimer said.

The “knuckle-dragging” mystery has challenged researchers for years.

“Walking on your knuckles is absolutely as odd as walking bipedally, a very peculiar way to get around. It doesn’t make sense, and it’s bothered anthropologists for years. Only chimps and gorillas do it. No one has come with the reason why—until now.”

Latimer teaches microscopic anatomy and evolution at Case Western Reserve School of Dental Medicine. The focus of his research is the evolution of human walking.

“To understand how humans walk and run,” he said, “you have to understand biomechanics.”

Latimer was joined in the research with C. Owen Lovejoy, a distinguished professor of anthropology at Kent State University, and Scott Simpson from the Case Western Reserve School of Medicine anatomy department.

Source: Case Western Reserve University [March 20, 2018]

TANN

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3 comments :

  1. Because we didn't come from monkeys! We were created in God's image as whole human beings. Each one according to it's kind as found in the fossil record.

    ReplyDelete
  2. It's not because Pan & Gorilla kuckle-walk and also climb trees & are mobile on the ground that their KWing evolved for these purposes. Most cercopithecines climb & run, but are palmigrade.
    Already in the 1990s, I showed that KWing evolved in parallel in Pan & Gorilla, and that humans never had KWing ancestors ("Australopithecines: ancestors of the African apes?" Hum.Evol.9:121-139, 1994. Google "Ape and Human Evolution 2018 made easy".
    In giant anteaters as well as chimps & gorillas, KWing reduces the gap between bi- & quadrupedality: unlike palm-walking, it lengthens the upper limb with the length of the metacarpal + the proximal phalanx. IOW, KWing facilitates switching between bi- & quadrupedalism. Anteaters frequently stand upright to destroy termite hills, and African apes had more bipedal/vertical ancestors (Verhaegen 1994). Probably also relevant is that both anteaters & the African apes had arm-hanging ancestors: not only with vertical spines (suspensory) but also with curved claws or fingers (preadaptation to KWing?).

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  3. These are just-so "explanations": it's not because humans walk/run with the feet/pelvis they have that these feet/pelvis evolved originally "for" walking/running. No cursorial mammal is plantigrade. No cursorial animal runs with vertical spine (is disadvantageous for muscle insertions, strength & equilibirum).
    The comparative anatomy & fossil evidence (incl.paleo-environment) are obvious:
    - Mio-Pliocene hominoids (including Dryopithecus, Oreopithecus, australopiths etc. & probably Ardipithecus) had already vertical spines & low pelvises, not for walking upright, but for frequently climbing vertically & wading vertically in the swamp forests where they fossilized, google "bonobo wading".
    - Early-Pleistocene archaic Homo dispersed intercontinentally, not running over savannas (eating what??), but along the coasts & rivers (aquatic food are rich in brain-specific nutrients: DHA, iodine, taurin etc.).
    Google e.g. "Ape and Human Evolution 2018 made easy".

    ReplyDelete


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