Nonsense. The first upright ape, according to this find was Morotopithecus and its close cousins had the potential ability of bipedal locomotion. It is possible that the other great apes had an ancestor that was able to walk upright. I have no reason to suspect that this fact, should it be true, means that current Evolutionary Theory as it now stands cannot explain it.
I have felt for some time that the capability for bipedalism would be older than currently theorized, and that the range of bipedalism vs quadrapedalism is more a matter of degree than of kind. Certainly all members of the hominoid superfamily are capable of walking on two legs in varying degree, as are many old world monkeys (the capuchin "organ grinder" monkey for example).
I looked up Morotopithecus and found several articles discussing the find, such as:
BU Professor Digs Up Clues To Human Origins
quote:
Most primate fossils that date to more than 20 million years ago show adaptations for movement on four legs, called quadrupedalism. The Morotopithecus discovery, however, shows a completely different locomotor pattern: suspensory locomotion, like swinging from branch to branch in trees.
This suspensory pattern is believed to fill an important transitional role in the development of primates. Many anthropologists believe primates evolved from quadrapedal ancestors into suspensory primates and finally into the bipedal creatures we see today in humans.
Morotopithecus shows a mixture of both primitive and modern features. It had a face and teeth resembling earlier species, while the lower spine, legs, and shoulders show a new design allowing suspension from branches. Being able to support an upright posture more easily than previous species meant Morotopithecus could more easily take advantage of the food and shelter found in trees.
Hanging from branches would tend to favor adaptation to a body capable of being verticle from head to toe, and would act to "pre-adapt" apes for occasional bipedalism.
(Morotopithecus would probably have not been exclusively bipedal from what I have read)
More like a baboon, a gibbon (without long arms), or an orangutan it seems to me. Capable of bipedalism but not attached to it.
That question can be asked without this being an issue, we are uniquely bipedal -why? The question is why did evolution modify this trait in us so that we are bipedal specialists
Because there was an opportunity for a bipedal ape and our bipedal capable ancestors were able to take advantage of it. Once taken there was not much opportunity for turning back.
Our spines of course, have been evolving for much longer. However, there is the possibility that our lineage flirted with both bipedalism and quadrapedalim for some time before evolving into the specialists we are.
Suspensory behavior would also adapt our spines (and hips and knees) for a vertical orientation without requiring much bipedal activity. And our necks and skulls, etc.
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