Skip to comments.Evolution's Poker Hand
Posted on 05/31/2005 4:48:54 PM PDT by RightWingAtheist
As I type these words, my fingers fly across the keyboard -- albeit not as efficiently as I would like. For one thing, I have never really been a 10-finger typist. For another, I have only 10 fingers. Surely, I could get this piece written and emailed to TCS Headquarters faster if I had, say, 12 or 14 fingers. Why don't I?
Although it might sound like I'm on drugs, the question I am raising is one that is of interest in evolutionary biology. Humans and numerous other species have five (or fewer) digits per appendage. Why? And moreover, why have selection pressures not given rise to appendages with more digits? A few extra fingers, after all, would allow more detailed grasping and other operations, and thus a mutation that provided them would seem like a good bet to spread through the gene pool.
The explanation, it turns out, tells us something not only about the evolutionary past but also about humanity's future -- about the potential and limitations of genetic engineering. In one scene in the 1997 sci-fi film Gattaca, a close shot of a pianist's hands reveals that he has six fingers on each (and thus he gives a virtuoso performance of "Impromptu for Twelve Fingers"). Just what would be involved in making such a concert possible?
Some 360 million years ago, at the end of the Devonian era, an evolutionary experiment was underway. Fish, which had long been the only vertebrates on the planet, were giving rise to tetrapods, animals with four limbs. The evolutionary link consisted of fish with two pairs of fins that gave them a survival advantage in shallow water (they could push themselves off if stranded, for instance). Some tetrapods had more than five digits on their appendages. One such animal, Aconthostega (a fossil of which was found in Greenland in 1987), had eight digits on each appendage (and had lungs as well as gills).
By 340 million years ago, there were tetrapods that spent much of their time on land, such as a small, lizard-like animal called Casineria (a fossil of which was found in Scotland in 1992). Casineria had five digits on each limb. Having relatively few digits may have been an advantage in making a land animal better suited for walking rather than aquatic paddling. Casineria also had more flexible digits (the fossil bones have furrows that once held ligaments) and a stronger backbone, key adaptations to land life.
A basic pattern of having five digits thus was set early in the history of land vertebrates. It seems to have taken hold before the evolutionary break between amphibians and amniotes (a broad category that ultimately would include dinosaurs, birds, reptiles and mammals). Many land animals today have fewer than five digits, but there is a notable absence of species that have more than five. This is not entirely surprising; in evolution, losing a feature that is not needed is relatively easy, compared to gaining (or regaining) a potentially useful feature.
Still, in the sweep of evolutionary time, one would expect some species to have found a survival advantage in having extra digits -- for example, in becoming better at tree-climbing or, in the case of more recent human ancestors, tool-making. The fact that this did not happen suggests that there are genetic constraints involved. Clifford J. Tabin of Harvard Medical School has suggested that the genes that control digit formation are structured so as to produce five basic patterns (thumbs, pinkies, etc., in the case of a human hand). Thus, additional digits that arise through genetic abnormalities merely duplicate an existing digit, and thus offer little survival benefit.
An even more daunting constraint appears to arise from pleiotropy, the capacity of genes to influence multiple physical characteristics. A rare genetic disease called Hand-Foot-Genital Syndrome involves malformations of the genito-urinary system as well as limbs; the cause seems to lie in incorrect coding across the same set of genes that handle digit formation. Thus, in the course of evolution, whatever advantage arose from having more digits may have come alongside the disastrous disadvantage of having malformed reproductive organs.
Vocal proponents and critics of genetic engineering both tend to assume that the technology is on the verge of transforming humanity. But the practical difficulties of achieving the hoped-for or feared transformation are too often overlooked. Perhaps, future genetic engineers will be able to create a 12-fingered pianist without unwanted side effects. Yet the complex evolutionary and genetic history behind having five fingers on each hand suggests that such virtuosity, scientific and musical, may be a long time in coming.
If you didn't "need" to change, you wouldn't be toilet trained now.
The change you are talking about is akin to replacing poopy diapers?
No, just don't anthropomorphize simple cells. A-G will do a very good job telling you that the answer to your question is a "will to live". She can do it much better than I.
Do simple cells exist to this day?
Not necessarily; they may just get in each others way. It's not clear that detailed grasping is needed for reproductive advantage.
Evolution is conservative; most things just hang around if not detrimental.
Thanks for the ping!
Texas Eagle, if you are interested in the discussion of the "will to live", here's a primary thread: Can the Monist view account for 'what is life?'
Experiments in robotics have shown that 3 digits is minimal..
Two "fingers" and an opposable "thumb"..
One thumb and one finger will allow grasping of an object, but control or manipulation is "shaky" as the object will rotate (laterally?) between the two digits...
digit #3 allows control of that rotation..
So one could argue, that for the sake of efficiency, humans could get rid of the 4th finger (pinky) and still have sufficient digital dexterity for any imagined task...
In many animals, an extra digit remains in the form of a "dew claw", which may be a disposed of thumb..
In hooved animals, the digits have evolved into 2 digits, (cloven hooved, like cattle and deer) and 1 digit ( hooved, like horses )..
The author looked in the wrong direction.. evolution "simplifies" ...
In different orders, digits have evolved to the task at hand..
Oh.. and then there's "flippers" on seals, etc.. and the whales... Once a land mammal, now sea-borne, and still retaining vestigial digits within it's flukes..
I once had a school buddy who was born with six fingers on each hand. He had scars from where the extra digits had been removed. I once told him he should searh the world over & find a six fingered girl to marry and he didn't think that was too funny at all.
Chimpanzees are not monkeys, nitwit, they are apes. How the hell do you expect anyone to take you seriously when you don't even get first-grade zoology correct?
I'm partial to the 'Big Smoke' theory, right after the 'Big Bang'.
It's not difficult to comprehend, and just about every one does comprehend it.
... and what is it about evolution that people turn aside all reason to deny it?
The belief that humans are somehow "special".
Welcome to Crevoland.
Which version of evolution are you talking about? The one I'm familiar with is a scientific theory.
It's just the usual chest-thumping for their side. They'll scream they're winning all the way to irrelevance and oblivion.
This is a rehash of "if we evolved from monkeys why are there still monkeys" question. In the same way, if Americans came from Europe, why are there still Europeans?
they were exempted from the forces that have acted on other forms of life for billions of years--seems strange that any old form including sharks and crocks would not have had major evolutionary change when the Evolutionist tell us that Evolution is such a powerful force- why are these life forms not effected???
Ever hear of a local fitness maximum? Top-level predators don't have much pressure to change. But that notwithstanding, what makes you think evolution has no effect on sharks?
Perhaps you misapprehend what the theory of evolution actually says.
Under the external hoof, horses have 5 digits
Not only do simple cells exist, the amoeba which is a one celled animal is literally a part of the first amoeba since they reproduce by division.
... evolution seems to have weakness in explaining major new species which are not able to reproduce with progenitors. Are we to believe that such changes must produce offspring of both sexes at the same moment.
...so no I do not refute evolution I just think that it may not be the primary vehicle for major change.
Again, it appears as though you labor under a number of misconceptions regarding the theory of evolution. You may be correct in that evolution may fall by the wayside, but I find it unlikely. However, should evolution ever be falsified beyond recoverability, I will cheerfully abandon it. Just remember that ID must stand or fall on its own merits.
How can they still exist if they reproduce by division? Once it evolved into something else wouldn't it divide itself into what ever form it evolved into?
Or are you saying those things live forever and the very first amoeba to ever exist still exists?
No, They don't..
"The horses foot contacts the ground only with the hoof of the third digit [like our middle toe] in an almost vertical position [like a ballet dancer, en pointe]," says Gheorghe M. Constantinescu, professor of veterinary anatomy, University of Missouri-Columbia and author of the book Clinical Dissection Guide for Large Animals.
Only splint bones alongside the cannon bone remain of its second and fourth toes. [P.D. Garrett, DVD, MS]
Moreover, the so-called cannon bone is much longer proportionately than ours.
What do I mean by "cannon bone"? Look at your foot.
The five bones going from your ankle to your toes correspond to the one bone in the horses foot: the cannon bone.
But, its huge running half way up the horses leg to what looks like its knee but is actually its ankle (called the hock).
Almost all trace of its other toes has vanished. Only splint bones alongside the cannon bone remain of its second and fourth toes. Short, strong ligaments tie the splint bones to the cannon bone.
That should read:
"A horse can still produce a mule..."
I'm not sure if this is scientifically correct, but the principle involved is the "differentiation" of the species of horse and donkey..
At some point, horses and donkeys split into two different breeds or species..
For a very long time, there was plenty of interbreeding, but over eons, the two species became less and less alike..
Such matings became "accidental" until man came along and started interbreeding on purpose..
Without human interference, ( and maybe in spite of it, ) horse and donkey will eventually be unable to interbreed at all..
Result,.. No more Mules..
While still closely "related" enough to produce offspring, they are generally infertile.
Occassionally a horse/jenny or donkey/mare offspring will be fertile and able to produce offspring..
What am I missing?
I think what is missing is Time.
The Salamanders have not remained distinct for a long enough period to completely become two different "species", if that's the right word..
Something similar was reported recently concerning birds that split their migration around the Himalayan mountain range.. ( National Geographic? )
Those that went North and East can interbreed...
Those that went North and West can interbreed..
Those IN the Northeast and Northwest cannot..
The two branches even have developed different coloration, as well as mating calls and habits..
Given time, the salamanders will become distinct branches of their species, with more than mating habits to differentiate them.. physical characteristics will eventually develop as well, to make identification of qualified mating material easier to identify..
The old "It's all random" argument..
Evolution isn't random..
I beleive in God, and God's creation of the Universe..
Second, I believe God created evolution..
I have no I repeat, no problem with the existance of God and Evolution in the same universe..
I don't see evolution as an attempt to discount the existence of God, I see it as an attempt to understand how God created the universe and everything in it..
That said, let's get back to randomicity..
All life has certain priorities, the foremost are survival and reproduction..
This fact (FACT) alone precludes the idea that evolution is a "random" process..
That which survives has the (an) opportunity to determine the characteristics of the following generation(s)..by passing on it's genes...
That which has the best chances for procreation, (health, choice of mate, health of said mate) are most likely to do so, and to produce healthy offspring, with the best survival characteristics..
Often, the environment in which that life exists can have a determining effect on which characteristics are emminently "survival" and "health" characteristics, and when (not if, when) that suited life "exhibits" certain feaures which identify it as more suited to survive, said life will increase it's chances at mating, and therefore, passing on it's survivability, health, preferable mating features, etc..
This is, in essence, evolution.. in it's simplist form..
As you can plainly see, it is not random..
I have pointed out the "external factors" that influence that life, and will, in Time, differentiate it from other life forms...
It has nothing to do with monkeys on typewriters...
It is not random..
It is evolution..
And like I said at the beginning, it does Not Exclude God in any way..
A God or Being, whatever or however you wish to describe It/Him/Her that can create a Universe, create the Physical Laws that govern Mass, Energy, Gravity, the orbits of Galaxies, Stars and planets, That created Elements in solid liquid and gas, and that created Life itself, is surely intelligent enough to create an orderly way in which to do all that and more...
Look to your Bible..
Man cannot comprehend God..
I suppose, if God had "wanted" to create Man out of the blue, God could very well have done so..
But, that would be like an "afterthought" wouldn't it??
If God were to create a Universe, and a place for man to live, called Earth, and all the Cosmos, wouldn't God just "do it" ???
Wouldn't God Just Do It, All At Once, and simply let the process happen?
well said , I will have plenty of time to see if evolution holds up as main engine of diversity of life - but those monkeys typing away over millions of years surely they have a shot at something great. Thanks for your discussion on a very polarizing subject..Peace thru strength.
I stand corrected.
i can understand those who would propose this ring data shows evolution - it well may- but you do not have a mule at the far end of the ring you still have a salamander with unique breeding habits.
what am i missing??
The fact that these two populations are reproductively isolated.
C - D / \ B E \ / A | F
A breeds with B, B breeds with C, C breeds with D, D breeds with E, E breeds with F, but A and F do not breed.
They are still technically classified as a single species, but incremental changes along the continuum have accumulated to the point that the ends of the ring function as separate species. Each end is free to drift (genetically speaking) independently of the other. What difference does it make if they don't breed because of coloration or sex organs or a funky mating dance? They are now separate and will in all likelihood continue to diverge.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.