How did the Jovian "Hidden Folk" evolve with legs? What was there for them to stand or walk on in the sky before they built an aerial town from hovering plants?
How did the Hidden Folk develop opposable thumbs? How does any animal? Based on something that I had read, I used to think that, on Earth:
quadrupeds evaded predators by climbing into trees;
they stayed in the trees long enough to develop opposable thumbs for grasping branches;
also, in the trees, they were free to chatter, which is the physical basis of language;
descending from the trees, their descendants walked upright with forelimbs freed to grasp, manipulate and make tools;
they also cooperated and conversed, thus becoming human beings.
Now I am told that the evidence indicates that bipedality preceded opposable thumbs so where did the bipedality come from? Once bipedality did exist, natural selection would favor the ability to manipulate the environment.
6 comments:
Kaor, Paul!
I think you touched on a weakness in THREE WORLDS TO CONQUER, when you asked how the winged Hidden People came to have legs and hands with opposable thumbs on Jupiter. Unless the Hidden Folk had first evolved on the surface before taking permanently to the upper atmosphere?
Sean
Bipedality seems to have evolved as a way to move more quickly on the ground by an animal that was gradually ceasing to be arboreal but was otherwise very like a chimp.
(It's very difficult to find the date of the divergence between our line and our last common ancestor with chimps because it was a "braided speciation" -- a gradual divergence, with episodes of interbreeding at increasing intervals over millions of years.)
But the early bipedal hominids, even after they walked upright habitually on the ground -- australopithecus, for example -- weren't -as- bipedal as we are; the shape of their hips isn't like ours, their arms are relatively longer, they didn't have the critical shape of the buttocks (which act as balance for us, substituting for a tail) etc.
They also seem to have spent a fair amount of time in trees and been edge-habitat dwellers.
The full adaptation to bipedalism seems to have come with h. erectus a little less than 2,000,000 years ago; erectus has a size and body-plan and proportions almost exactly like ours, except that their skeletons are more robust.
The differences between us and them are almost all above the neck. We walk and run exactly the way they did. And we do it very well; human locomotion is extremely energy-efficient and in some aspects of it we're the world-beaters among mammals.
Dear Mr. Stirling,
I'm very enthusiastic about these fascinating notes you write. A sentiment I'm sure Paul agrees with. Many thanks!
You make me very regretful about how little I know about anthropology, only some bits I've picked up over the years, esp. the works of Poul Anderson. Or, oddly perhaps, some of the works of Pere Teilhard de Chardin.
Hmmm, so all hominid lines descended from Homo erectus? But before that it gets more uncertain? Understood!
Bipedality has certainly been a blessing for mankind, but it comes with some costs! I had a nasty fall in October and got a painful case of tendinitis in my left ankle. It's slowly getting better but I still have some pain. And has definitely slowed me down.
Sean
Sean: well, we're getting into the age when our evolutionary role is to be eaten by hyenas... 8-).
All -extant- hominid lines are descended from Erectus (and so were Neanderthals and Denisovians). There were others at the time that have gone extinct since.
The uncertainty I mentioned is way, way back -- among the earliest hominins, and that period is very poorly understood at present.
The -genetic- evidence for the "last common ancestor" with chimps -- is rather contradictory so far, giving variable dates, from as far as 11-12 million years and as recently as 5-6.
The problem is that different chromosomes show different dates of divergence.
The explanation is probably that rather than a clean split between the lineages, there was a long period -- up to four five million years, ending as recently as about 5-6 million years ago -- when there were hybridization events between the diverging lines. They were gradually separating but still interfertile and interbred now and then.
The same thing seems to have happened with the gorilla lineage, a bit earlier.
Speciation in the great apes (which, effectively, we are too) seems to have been "sloppy", so saying precisely when the last common ancestor lived is sort of arbitrary.
Dear Mr. Stirling,
Too true, alas, that we are reaching the age when we become potential food for hyenas! (Smiles)
Again, thanks for writing fascinating comments! So, up to about 4 or five millions years ago, the lines leading to the hominids were still inter fertile with chimpanzees.
I had thought the hominids were LESS closely related to the great apes than we are to the chimpanzees. Probably the definitive split off from the apes was longer ago than from the chimps?
Sean
Likewise. (To the "fascinating.")
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