The Evolutionary Utility of the Opposable Thumb

Factual Questions
1

Would I be safe in assuming that I am not alone in having had spoon-fed to me, along with the rest of the public school curriculum, the notion that one of the really prodigious evolutionary strides of our species was stridden when we rearranged our metacarpals and phalanges and ended up with opposable thumbs?

We of the five digits, in the form of 4 fingers and a convenient thumb that closed towards them in the opposite direction, were by virtue of that design said to be toolmakers and tool-deployers. Toss a couple hundred millennia of learn-and-extend on top of “hey check it out, stone scrapers” and you’ve got homo sap footprints on the moon and urban blight and reality television, yeah? no?
Question the First: Actually, didn’t other species with no more of a head start develop that general kind of arrangement at least as early if not earlier (e.g., some of our primate cousins, who seem to have it in their feet as well as their hands), and yet have not manifested any serious tool-using tendencies as a consequence thereof?

Question the Second: Opposition could exist and could manifest in other configurations of the subject at hand. (Sorry). You could theoretically have three fingers and two “thumbs”, or three and three. Have other configurations of the “opposable thumb” adaptation shown up as parallel grasping & holding “strategies”?

2

The opposable thumb was a significant evolutionary advancement, but it began earlier in primate development than it appears you’ve been taught. Larger, more complex brains and walking upright were later developments that were a bigger leap.
Wikipedia has a list of non-ape animals that have thumbs of some sort, like the Koala, who has two opposing digits on its hands.

3

A koala has two digits on its hands and they are opposed, or a koala has two “thumbs” and x fingers that the thumbs oppose?

re: the brain thing, it was always said that having the opposable thumb set the stage for the bigger brain, sort of a “we’ve got the chassis, let’s drop in a better engine”. Tool use --> greater utility of a bigger brain if a bigger brain develops, etc.

4

Two “thumbs” and three “normal” fingers. Like on [url=http://www.koalaziekenhuis.nl/img/il-hand.gif] thi drawing.

5

Damn, forgot slash in closing tag. Correct link.

6

I would think the opposite, that opposable thumbs evolved because our ancestors had the brains to make real use of them. I suppose it takes quite a bit brain-power to quickly grab onto branches and swing around. You do, after all, have to offset the lost advantage of running really fast.

But anyway, without doubt, the real thing that led to our brains wasn’t the evolution of some big, noticeable, “god-why-didn’t-we-think-of-this-before” feature, but the evolution of the genetic blueprint mechanisms which could handle the planning and development of such a complex a thing. Also, it took time for evolution-enhancing shortcuts/prototype patterns/homeobox-type-genes to be developed and customized for brain development.

Whenever you see anything impressive in evolution, you should never just assume that evolution hadn’t realized before how good such a thing would be. Evolution isn’t so poor at its job as such a view implies. Although few biologists realize this too acutely now, the real thing which does most of the labor of evolving over the eaons isn’t the limbs or breeding behavior or other end-user features (so to speak), but all the peripheral equipment which does the work of accelerating the evolution of those things. I suppose it is another thing that many biologists don’t give much thought: that evolution isn’t so ineffective as to let mutations be completely random. That it would construct proteins one amino acid at a time, or leave the generation of variation alone to dumb mutation. Even with natural selection, such a ridiculous scheme would never work. Things like symmetry and segmentation are the most simple to understand examples of the evolution of accelerating mechanisms. Homeobox genes are another, although it takes a second to realize that they are not simply triggers for development, but tuning knobs for evolution. Other features like introns (the real reason, imo, why eukaryotes were able to have organelles), are more sophisticated devices whose purpose can only be wildly speculated now.

7

Actually, one of the little theories I’ve been fond of for awhile is neoteny — the notion that homo sap are “born premature”, retaining characteristic that other primates have in earlier embryonic and fetal stages, the key one being the softness of the bones of the head. Advantage: that huge brain-filled head can pass through the birth canal. Other neotenous characteristics that get tossed in for free, so to speak: tiny brow ridges, absence of tail, the angle of the foramen magnum opening with regards to the orientation of the head (this one is important for upright walking — in other primates it apparently kind of gravitates more to the back of the head, so that the head more easily faces forward when down on all fours), significantly less hair, and less jaw musculature.

It’s interesting to think of all of these different evolutionary changes as really being manifestations of a single change, no?

As far as I know, though, it doesn’t have any implications for the five digits / opposable thumb thingie.

8

[QUOTE=Alex_Dubinsky]
I would think the opposite, that opposable thumbs evolved because our ancestors had the brains to make real use of them. I suppose it takes quite a bit brain-power to quickly grab onto branches and swing around.
[/QUOTE]

Opposable digits have nothing to do with brain power, and nothing to do with moving fast. Chamaleons have opposed digits (arranged 3 and 2) on front and hind feet, but are not very brainy and are exceptionally slow moving. Likewise koalas are not terribly bright, and are also slow moving. Several very slow-moving primates like the slow loris and the potto also have opposable thumbs. Opossums have opposable digits, but are neither bright nor exceptionally swift.

Opposable digits are an adaptation for climbing by means of gripping (rather than by using claws). They have little to do with anything else. They are a basal (“primitive”) characteristic among primates; even the prosimians have them.

Simply having an opposable thumb is not the thing that facilitates tool manufacture and use in humans. Instead it is the precision with which the thumb can be opposed to the other fingers.

The basic hominid adaptation is neither our hands nor our brains, it is our legs. Bipedalism is the key evolutionary development that distinguishes our line from other apes. Bipedalism, by freeing the hands from locomotion, was what made the human precision grip possible.

9

[QUOTE=Alex_Dubinsky]
I suppose it is another thing that many biologists don’t give much thought: that evolution isn’t so ineffective as to let mutations be completely random. That it would construct proteins one amino acid at a time, or leave the generation of variation alone to dumb mutation. Even with natural selection, such a ridiculous scheme would never work.
[/QUOTE]

I have to wonder whether you simply don’t know what the theory of evolution as elucidated by biologists actually says, or if you have developed your own novel “theory of evolution”.

At any rate, yes, mutations are random, and proteins are indeed constructed through tiny, accidental modifications of their structure. That’s what evolution is; it doesn’t operate towards an end as you describe - not unless you mean to describe some religious belief that you’re calling “evolution” in order to be deceptive.

10

Well right, exactly. If you’re slowly grabbing branches and aren’t swinging around, a simple brain will work well. However, being very slow is also a huge disadvantage, which is why only a few creatures take up that path. A thumb on a non-tree-grabbing creature is only a liability for injury. You misread me a little, so let me know what you think of the clarification.

Bipedalism and thumb precision are pretty clearly (at least to me) enabled by a powerful brain as well. It takes a lot of calculation for such precise sensing and positioning.

I agree. That may very well have been (hell, i mean probably was) evolutionary history. However, it is by no means a contributor to our intellect. How ridiculously easy must it be to just slow down development? No new feature or protein is even really being added.

The things whose evolution is most responsible for our intellect weren’t just tiny, seemingly-obvious fixes to physiology, like soft heads, undeveloped bodies, big brains, or opposable thumbs. Rather, they changed the fundamental dynamic and advantages of growing large brains. They made them wireable and useful, initiating all those secondary modifications.
Excalibur, I am not claiming evolution operates toward an end other than propagation. I am claiming that natural selection would have evolved mechanisms to make natural selection faster. Such as sex, symmetry, and repetition. As well as much more subtle mechanisms, such as junk dna. They are the reason that over the course of the earth maximum complexity has grown exponentially while the number of individual*generations (among those record holders) has generally dwindled.

Yes, that’s not what biologists are talking about now. However, maybe they should be.

11

[QUOTE=Alex_Dubinsky]
I am claiming that natural selection would have evolved mechanisms to make natural selection faster.
[/QUOTE]

You do realize that this statement is nonsense, right?

12

no, no I don’t. ok, maybe I should have said “natural selection would have evolved mechanisms to make evolution faster.” Does that change much? If not, please explain.

13

[QUOTE=Alex_Dubinsky]
no, no I don’t. ok, maybe I should have said “natural selection would have evolved mechanisms to make evolution faster.” Does that change much? If not, please explain.
[/QUOTE]

Natural selection is not a “thing” upon which, well, anything can act. Especially not “itself”. It is a shorthand for statistical probabilities; it is the sum total of all external forces, events, conditions and happenstances which affect the relative frequencies of gene alleles within a population. As such, there’s really no way for natural selection to feedback on itself (keeping in mind there is neither an “it” nor a “self” involved…) to make itself faster / more efficient / whatever.

Remember that natural selection is simply an analogous process to artificial selection. Except, instead of humans selecting individuals based on traits which we desire, nature is “selecting” organisms based on traits which are most advantageous to themselves. Advantages and disadvantages are translated into likelihoods of success or failure in terms of passing one’s genes on to subsequent generations. Regardless how populations evolve under the scrutiny of NS, NS will still operate in the same way.

14

[QUOTE=Alex_Dubinsky]
Bipedalism and thumb precision are pretty clearly (at least to me) enabled by a powerful brain as well. It takes a lot of calculation for such precise sensing and positioning.
[/quote]

And you would be wrong to think that. Australopithecines had brains much more akin to those of chimps than humans, and yet they walked upright.

I’m inclined to think they probably have a better idea what they should be talking about than you do.

15

[QUOTE=Alex_Dubinsky]

Bipedalism and thumb precision are pretty clearly (at least to me) enabled by a powerful brain as well. It takes a lot of calculation for such precise sensing and positioning.

[/QUOTE]

Which is why Ostriches are so much smarter than Elephants. Bipedalism doesn’t require much brain power. Have you seen an ostrich head?

16

[QUOTE=Darwin’s Finch]
Natural selection is not a “thing” upon which, well, anything can act. Especially not “itself”. It is a shorthand for statistical probabilities; it is the sum total of all external forces, events, conditions and happenstances which affect the relative frequencies of gene alleles within a population. As such, there’s really no way for natural selection to feedback on itself (keeping in mind there is neither an “it” nor a “self” involved…) to make itself faster / more efficient / whatever.

Remember that natural selection is simply an analogous process to artificial selection. Except, instead of humans selecting individuals based on traits which we desire, nature is “selecting” organisms based on traits which are most advantageous to themselves. Advantages and disadvantages are translated into likelihoods of success or failure in terms of passing one’s genes on to subsequent generations. Regardless how populations evolve under the scrutiny of NS, NS will still operate in the same way.
[/QUOTE]

Generally, yes. I mispoke, and had meant “evolution,” not specifically natural selection. However, under some definitions, I wouldn’t agree that natural selection cannot change.

For example, (and this is hypothetical) what happens if a species evolves to be intelligent enough to look at each other and have an idea of who is fit and who isn’t. At first, this may start out very simply as the animals which look healthy and well-featured attract more mates (although, even at that point, the process has gotten pretty sophisticated). However, with further advancement, the overall process may honestly resemble artificial selection more than natural.

Now, since natural selection isn’t usually defined as only being powered by survival until reproduction (or by some other narrowly-delineated mechanism), it really isn’t clear that you have the right to claim there to be a very sharply drawn line against improvements to natural selection.

To argue more effectively with an example, humans in times of little food are more likely to think plumpness to be attractive. While natural selection for even blind organisms would push towards the energy-stockpiling adaptation, the process has been improved and has gotten faster because of the evolution of our brains along with the instincts which make us think that way.

Who knows, maybe we should start changing our definitions. But for now, let’s not start arguing from them. Actually, let’s not ever argue from definitions (even though it’s so easy and seductively straightforward). If taken too far, all it does is let strictness of language limit the reach of thought.

[QUOTE=Excalibur]

.
And you would be wrong to think that. Australopithecines had brains much more akin to those of chimps than humans, and yet they walked upright.
[/QUOTE]

Australopithecines were smarter than chimps and could walk better than them. Chimps and other apes can walk too, but they’re also very smart. Other animals sometimes stand up in the wild, but very few are able to walk far before falling over (at least without lots of training). If you say humans train themselves for walking, then try watching the olympics and seeing what trained humans are really capable of (to compare effectively).

You can’t build a segway with a pocket calculator. You need brains for these things (bipedalism and movement precision).

Man, what’d you do? Wake up on the smartass side of the bed?

17

[QUOTE=Lemur866]

Which is why Ostriches are so much smarter than Elephants. Bipedalism doesn’t require much brain power. Have you seen an ostrich head?
[/QUOTE]

Good point. I actually started thinking about dinosaurs (well, two-legged raptors) and birds (who evolved from them) before I had read your post. Raptors were the smarter members of their kind, and birds show some pretty damn sophisticated behavior too (during migrations, mating rituals, and FLYING for crissakes) Their brains are small, but they seem tightly packed and especially tuned for coordination. Remember, bird/dinosaur brains and mamallian ones took rather long-diverged courses of evolution and so their sizes cannot be directly compared.

18

[QUOTE=Alex_Dubinsky]
Australopithecines were smarter than chimps and could walk better than them. Chimps and other apes can walk too, but they’re also very smart. Other animals sometimes stand up in the wild, but very few are able to walk far before falling over (at least without lots of training). If you say humans train themselves for walking, then try watching the olympics and seeing what trained humans are really capable of (to compare effectively).

You can’t build a segway with a pocket calculator. You need brains for these things (bipedalism and movement precision).
[/QUOTE]

You’re so scattered that I can’t tell what you even think you’re saying. At any rate, the evolutionary line that led to humans developed true bipedalism long before it developed human-like brains. All bipedalism requires, anyway, is a bit more motor sophistication. I’m not sure why you imagine it’s such a challenge.

19

My chihuahua does pretty impressive little stints as a biped and she doesn’t even have the hips or neck for it. Still manages to balance on her back feet and walk around for several minutes when she thinks whatever I’m doing in the kitchen might lead to food for her. If it takes a big brain to manage bipedal locomotion even when you’ve got the skeletal architecture for it, I’d imagine it would take an even bigger one to carry it off when you don’t.

Trust me — she’s cute and, for a chihuahua, rather sweet, but not really the sharpest spine on the cactus.

20

[QUOTE=Alex_Dubinsky]

For example, (and this is hypothetical) what happens if a species evolves to be intelligent enough to look at each other and have an idea of who is fit and who isn’t. At first, this may start out very simply as the animals which look healthy and well-featured attract more mates (although, even at that point, the process has gotten pretty sophisticated). However, with further advancement, the overall process may honestly resemble artificial selection more than natural.

[/QUOTE]

This process is generally known as sexual selection. But it isn’t tied to increased brain power, rather some simple signal that potential mates respond to. So female peafowl dig peacocks with big fancy tails. They don’t have sophisticated brains that tell them that a peacock with a fancy tail is more likely to be fit/healthy than a peacock with a raggedy tail, they just dig bad boys with big tails. And so in a sexual arms race tail sizes increase to the spectacular sizes we see in peacocks today. Or it could be something else…a particular song, a patch of feathers, a mating dance, different species have different signals.