The fact that humans have opposable thumbs is often used as a sure sign of our evolution.?

Question

How does it?

Answer 1

A single feature of a single species is not evidence of anything. It has to be a *shared* feature with a certain *group* of species.

So if it was only humans that had opposable thumbs, then this would not be a sign of anything, much less a "sure sign". But people who think that humans are the only species with opposable thumbs are just wrong.

If anything the opposable thumb is more an explanation for why there is larger brain development in primates, compared other mammals.

But it is *SEVERAL FACTS ALL CONSIDERED TOGETHER* that provide considerable evidence for relationships through common ancestry to other primates who also have opposable thumbs ... and thus for evolution. Any one of them is just a piece of evidence ... and may even have other explanations. But put them all *together* and no better explanation stands.

What do *you* think all the following facts add up to?

(1) All apes have opposable thumbs. (Chimps, bonobos, gorillas, orangutans, and the many species of gibbons.) This is a *sign* (piece of evidence) that humans are related to (share genes with) apes.

(2) All Old World primates, have opposable thumbs. These are all the African and Asian monkeys, and all the apes (as they are also all from Africa or Asia). This is another *sign* (piece of evidence) that both the apes and the humans are related to (share genes with) Old World (African and Asian) monkeys.

(3) All New World monkeys do NOT have opposable thumbs. (These are the monkeys of South and Central America.) This is another *sign* (piece of evidence) that humans, apes, and Old World primates are more closely related to each other, than any of them are to the New World primates.

(4) Almost no other mammals (with a few notable exceptions) have opposable thumbs. This is another *sign* that humans and apes are more closely related to Old World primates than they are to other mammals.

(5) The rare exceptions tell us even more. Some New World monkeys do have opposable thumbs ... and there are some non-primates (like koalas) that also have opposable thumbs. The genetics and exact structure of these cases shows that they arrived at opposable thumbs independently (what's called 'convergent evolution') rather than through the same genetic path.

(6) There are lots of other features that independently confirm the same genetic relationships. For example, humans, apes, and Old World primates all have color vision, while New World primates (and other mammals) do not.

(7) The fossils of all other extinct Hominids all show the bone unmistakeable structure of opposable thumbs on the hands. This is a *sign* (piece of evidence) of an unbroken line of ancestors all of which had opposable thumbs. For example, if Homo erectus or Australopithecus did *NOT* have opposable thumbs, then this would be a big blow to the picture of human evolution.

(8) The fossils of Hominids also show the distinct signs of ever diminishing opposable thumbs *on the feet*. This is a *sign* (piece of evidence) that these fossils trace a lineage tracing back later Hominids (like Homo erectus) to earlier ancestors that had grasping toes.

(9) Look at your own foot. The human foot has distinct signs of you having an ancestor that once grasped with the feet:
(a) You have two bones in your big toe (one less knuckle) just like your thumb ... where as the other toes like your other fingers, all have three bones (one more knuckle).
(b) There is a muscle in your calf (the Plantaris muscle) that is long and weak with no actual purpose in humans. (In fact, it is often harvested for reconstructive surgery, with no effect at all on walking. And 9% of humans are born with no Plantaris muscle at all.) However, the Plantaris muscle is used in other primates for *grasping* with the feet.
(c) Your big toe has more nerves and muscles ... which is why you can wiggle your big toe independently of the others.
(d) Both your thumbs and your big toe are on the inside ... and are bigger and fatter than the other digits. There is no structural reason for this ... other than opposability.

All of these facts *TOGETHER* paint a clear picture: The genes for opposable thumbs (and other features like color vision) appeared in the primate line *AFTER* the continental drift caused the African and American continents to drift apart. And the genes for opposable thumbs in the *feet* have been suppressed because of upright walking ... but there are still signs that these genes are still there.

Evidence, evidence, evidence.

Just as a lawyer would never walk into a courtroom with a single fingerprint ("humans have opposable thumbs") ... but with a *lot* of related evidence that *together* produce strong evidence. There is never a single "sure sign" ... it is always a *collection* of evidence, that when considered together, has no better explanation.

Answer 2

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RE:
The fact that humans have opposable thumbs is often used as a sure sign of our evolution.?
How does it?

Answer 3

Do Chimpanzees Have Opposable Thumbs

Answer 4

Having opposable thumbs means we can actually pick up an object, turn it around and look at it very carefully. Only the primates can do this........imagine a dog or a cat trying to pick something up with its paws? impossible.
Because we have such nimble fingers and thumbs we are able to examine objects in such a way that it stimulates thought and increases our intelligence. Theory suggests this also allowed us to make tools and manipulate objects (ever seen a chimp poking ants out of a termite hill with a long stick?) and increase our survival. It all fits with survival of the fittest and I think its a pretty reasonable suggestion.

Answer 5

Do Chimps Have Opposable Thumbs

Answer 6

The only part of your anatomy that is a sign of human evolution is the brain, specifically, how it is used. Many other animals have oppositely arranged digits. Like the raccoon. Raccoons are not evolving to replace humans. So, claiming evolution works or does not work based on a single anatomical structure seems to be poor use on that piece of anatomy that makes you superior to other animals.

Answer 7

It depends on what aspect of evolution you're talking about.

When dealing with microevolution, the appearance of opposable thumbs could be viewed as an adaptation to more effectively utilize the environment.

If you are referring to macroevolution (apes -> humans), there is no correlation whatsoever. In fact, there are no sure signs of [macro]evolution in general.

The normal argument is that both humans and apes have opposable thumbs (and other things, like 99% shared DNA), and therefore, "logically", humans evolved from apes. I don't want to start a religious flamewar, so I'll make this as short and objective as possible- macroevolution violates the "disproving of spontaneous generation", and is therefore invalid. When macroevolution is proven, then you can worry about the specifics.

Answer 8

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Answer 9

False.
Evolutionary theory is based on studies involving populations of species.

Looking at one specific feature of one species doesn't have anything to do with evolution. That's anatomy.

Answer 10

It is not evidence of evolution any more than it is evidence of design.

It is an example of the evolutionists argument of homology.
Evolutionists that use this argument need to examine the evidence and the logic of their argument.

Homology involves the theory that macroevolutionary relationships can be proven by the similarity in the anatomy and physiology of different animals. Since Darwin, homology has been cited in textbooks as a major proof for evolution. A review of the literature on homology indicates that the theory does not provide evidence for evolutionary naturalism, and that the common examples of homology can be better explained by Creation. Furthermore, increased knowledge about the genetic and molecular basis of life has revealed many major exceptions and contradictions to the theory which, as a result, have largely negated homology as a proof of evolution.
http://www.creationontheweb.com/content/view/1818