Human evolution; onset of bipedalism (Introduction)

by David Turell @, Saturday, June 01, 2019, 20:51 (141 days ago) @ David Turell

Current research:

https://www.sapiens.org/archaeology/human-bipedality/

"Fossils suggests that bipedality may have begun as early as 6 million years ago. But it was with Australopithecus, an early hominin who evolved in southern and eastern Africa between 4 and 2 million years ago, that our ancestors took their first steps as committed bipeds. Yet scientists still know little about the circumstances that led to this trait’s emergence.

"Carol Ward, a paleoanthropologist and anatomist at the University of Missouri, studies this question. A specialist in human origins, Ward has spent a number of field seasons at various paleontological sites, including at Kanapoi and Lomekwi in West Turkana, Kenya, where she and her colleagues recovered australopithecine fossils. Her latest work repurposes 3D medical-imaging technologies to compare modern primate anatomy, including soft tissues and organs, with the skeletal fossil record of ancient hominids.

"The way that humans get around the world is different from any other animal on Earth. We move around on the ground, upright on two feet, but in a unique way: with one foot after the other, holding our body fully upright in a characteristic series of motions. This is something that no other primate does, and it seems to be a behavior that was present in some of the earliest members of our branch of the family tree. It represented what was really the initial major adaptive change from any apelike creature that came before us.

***

"... the fossil record tells us that we began to walk upright on two feet maybe between 6 and 4 million years ago. Brains in early hominins really don’t start to get large until after 2 million years ago, so for the first two-thirds of human evolution, brain size change wasn’t really a major event.

"We have many apelike creatures that lived in the Miocene, between 23 and 5 million years ago. There’s nothing really like us at this time. And then there’s a gap in the fossil record, largely because of geologic happenstance, if you will. There aren’t many sites at the right time and place that have any fossils. And then all of a sudden, around 4 million years ago, we have these committed bipedal animals, and we don’t have a great fossil record of transitional forms.

That said, sometime between 7 and 4 million years ago a number of primates appear to have developed upright postures, but nothing as developed or specialized as we see later on. So we may be starting to get a little window on this time period.

***

"Taking my perspective in looking at the torso, combined with the new things we’re learning about australopithecines, we are finding out they’re not quite as chimp-like in all ways as we thought. Dipping further back in time, into the ape fossil record, we are finding out those things aren’t very much like modern chimps either. You map that onto the whole tree and apply the basic principles of parsimony (what’s the simplest way this could have happened?), and it’s really supporting the hypothesis that’s been around for a long time: that maybe we didn’t evolve from something that was just like a modern chimp or gorilla. But now we’re able to show in which ways ancient hominids might have been similar or different. And that’s going to help us get a much better picture of what the ancestral condition was that led to bipedality.

"Natural selection can only work on “last year’s model.” If you want to understand why something happened, you need to understand what happened."

Comment: It seems as if our evolution from the ape group was really very special. We are certainly not chimps. Note the late development of the larger brain as compared to the early bipedal posture. The hands for different uses preceded the brain development. Seem logical to me as God did His work.


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