If I understand natural selection correctly - a mutation will eventually spread throughout a population if it gives member of that population a reproductive advantage.

A accept that more cave fish will lack eyes than other species, as it doesn't matter whether they can see or not. To the seeing cave fish - they are as good as blind in their environment, regardless of vision. However, why would being born without eyes lead to a reproductive advantage? Or is it just a matter of the seeing cave fish seeing light - swimming towards it, and thus leaving the environment? While the blind cave fish would have other reasons for staying. Food, calm water, consistent temperature, etc. - with no external stimuli such as light to encourage them to go anywhere else.

Never mind. I think I answered my own question.

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Spock Jenkins of the Vulcan Jenkins'.

because in the dark they offer no advantage a fish with a mutation that resulted in no eyes wouldn't be selected against, also the resources needed to develop eyes would be used elsewhere,. A damaged eye could result in infection and death. So a fish with no eyes has a slight advantage.

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'The eye can only see what the mind is prepared to accept'

Unless the eyes are tuned for infrared and detect heat instead of light.

Growing a complex sense organ like an eye requres energy and biological resources (such as RNA) that can be dedicated to strengthening or improving other parts of the fish's physiology. Growing an unneeded organ is wasted effort.

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

Well, and as hinted on with the damage/infection post; an eye is a huuuuuge weak spot, defensively speaking. Get rid of it, if not needed.

As for reproductive advantages; if the female fish has eyes, and some annoying cave-diver comes by with a light,she might see her mate and realize how unattractive he is.

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I'm like one of those idiot savants...well, except for the savant part.

Theory of Zombie Relativity:
1) Everyone Else is a Zombie relative to You
2) Whether or not it matters is related to the inverse square of the distance between their teeth and your brain
(Quoted from Demigrog)

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

It takes a very long time before the 'colony' of cave fish has lost their eyes.
Even then it's faster on the evolutionary scale than normal. Simply put, there is a slight advantage as has been pointed out. That slight advantage alone isn't enough all by itself, unless it's repeated and reinforced.
The fish trapped in the cave will suffer mutations at the same rate. Yet because they are more isolated, the mutations (including no eyes) will have a better chance of making it into a larger percentage of the gene pool. Not that I am saying these fish were inbreeding exactly, but very close to it

There is truth in saying that the resources are better used elsewhere if eyes are useless.
However, I must also point out that DNA is not intelligent and it does not willingly decide that resources are going to waste. It just follows its programming.

The reason others said that a wasted resource may evolve out is because of the advantages of it on an evolutionary scale- Not because the body knows that a resource is going to waste and 'mutates' at will.
There are many examples of 'wasted organs' in animals today that have not evolved out. Without a driving force to make it advantageous enough for trial and error to weed out the most advantaged mutant.
See the thread : Darwin Was Wrong that Coliver started that addresses this (Warning I was on the wrong side of the fence in that thread and had to be corrected swiftly- This resulted in something of a religious revolution in me...)

All of this (so far in this post) is based on the assumption that a mutation is necessary.

However, animals in captivity and humans in society have been observed to be born without eyes and with white blank blind eyes.
It seems that in many species, this mutation has already occurred. The gene for it is highly recessive. If born in the natural state, an animal will not live long blind (A human will live much longer because of society and perhaps contribute his gene back into the gene pool). Seeing blind animals in the wild is beyond rare. But the gene is there as observing births in captivity demonstrates.
With a recessive 'no eye' gene, a trapped cave species will no longer have those blind individuals singled out, and with even a slight advantage of having no eyes, their gene will eventually take dominance.

One thought that comes to mind is that vision takes quite a bit of the brain's capacity. That suggests vision requires resources (nutrition & oxygen). In a dark cave where eyes are useless, those born without eyes wouldn't have to waste resources on a useless organ. Perhaps that is the evolutionary advantage to not having eyes where they serve no purpose. I speculate that eyeless creatures would be better adapted to survive under those circumstances.

What if we turn this around. Andrew Parker Ph.D., a marine biologist and evolutionary scientist, has suggested that a major reason for the Cambrian explosion was the acquisition of vision. Now, this is certainly conjectural and refers to the very earliest of Cambrian times where the fossil record is very sparse. But, in the context of the current discussion, could we hypothesize that eyesight became important because the arthropods and other forms were living in an environment where light was adequate for vision to be an advantage? It is always assumed that these early Cambrian communities were near shore and there is ancillary evidence of such, could we then add development of eyesight as another suggestive piece of the puzzle for where they lived, in the light? Trite as this seems at first blush, it is not proven. As it has been stated earlier in this thread, vision takes resources from the organism. (An example might be that blind people learn higher levels of hearing discernment.) Therefore, if indeed vision was a driving force of the evolutionary expolsion of divirsification, could it have caused a shift of living environment from deeper waters to a more near shore one where there were more plants, i.e. food, that also fueled the explosin of life?

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(By the way, I hate it that so many papers in the areas of planetary science and geology are not easily avaiable to the dreaded "non-subscribers". It is like they are screaming at me: "YOU CAN'T HANDLE THE TRUTH". Good, I feel better now.)

I know you are a person who takes his physics seriously, but isn't it said that most great discoveries aren't discovered with "Eureka!" but with, "Hmmm, that's funny." Big Don

<<Growing a complex sense organ like an eye requres energy and biological resources (such as RNA) that can be dedicated to strengthening or improving other parts of the fish's physiology. Growing an unneeded organ is wasted effort.>>

Yep--even nature has a budget.

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"Call me old-fashioned, but I think fire is magic. And it scares me a lot."

--The State

What I don't get about this is where the mutation(s) come[s] from. It's not exactly common, in a species with eyes, for individuals to be born/hatched without them or with reduced or deformed ones.

On the time scales that we are talking about, it doesn't need to be common.

And bear in mind that there are a great many mutations. You and I probably have a bunch in our own DNA code.
From faulty vision (needing glasses - I don't need them but that is a common thing with people) to crooked teeth (not that these are always caused by mutations- but can be sometimes.) or even balding. Balding in men has not shown to be totally disadvantageous- so the mutated gene from long ago is still common in men to lose their hair. In women however, balding is a disadvantage and the gene is more rare in women.

Polydactilism, for example, is very rare (highly recessive gene) in humans. Some dogs and cats get more instances of it. But it does appear time and time again.

Now should a colony of humans get trapped in a cave (that has glowy worms for light or something) and polydactilsim demonstrates an evolutionary advantage for some reason, especially with breeding with the larger population outside cut off- given the time scales- it will become more and more dominant as the breeding spreads the gene through the whole colony- and those who have it are favored by the advantage of it.

As far as where mutations come from- Animal DNA is a very very very long sequence. It's almost amazing that as few mistakes are made.
Enzymes go up and down the string checking and rechecking and correcting errors. But not all errors will get corrected- some will be missed- Viola- mutation. Many mutations simply result in a slight discomfort, a strange appearance in some way or some can result in death, inability to function etc. Depending on the severity of the mutation.

They can also be 'forced' by radiation, and even certain chemical exposure.

Remember the 7-legged hermaphrodite deer a few months back?

Once a mutation arises- if the mutant breeds, those mutant genes are also passed on to its offspring. As a recessive gene, they will most likely not appear in the offspring but will still be in the DNA code. Once it is in the offsprings code- the DNA does not 'realize'* that it is an error or mutation. The mutated gene 'becomes' the original code. As the enzymes work over the DNA correcting errors, it will leave the mutated gene alone because it has no basis to 'assume'* that it should be otherwise.
Also it will even correct a gene sequence back to the original mutation should it discover an error in a mutant gene. Once mutated- it will stay that way. The only way for it to be eliminated would be for all those that carry the gene to not breed or not survive long enough to breed.

So if that 7-legged hermaphrodite deer had sired offspring prior to its death- those genes are now in that herd (At least its offspring) and should those offsrping all breed- so on and so on.



* these words are used for descriptive purposes to demonstrate the programmed nature- not intellect.

The only thing I would suggest is that the seven legged hermaphrodite deer is more likely two fraternal twins that somehow combined in utero rather than a true gene mutation. But not having read the story - my guess is based solely on this thread.

I still like my idea. Sightless animals were prone to stay due to still waters and consistent termperatures. Sighted animals were prone to leave and swim toward any light they might see. But I also see merit to the whole, "you could poke your eye out" survival factor in complete darkness. I would also think that sighted fish might see just enough, even in almost total darkness that they would make decisions trying to rely on their sight to get around. However, sightless animals would have no such crutch and would more willingly defer to sound, vibration, and touch - making them more likely to find a mate in the first place.

Evolution is fun. More people should embrace it rather than fear it. It only took me a bit over 30 years to get it, when everyone around me was teaching otherwise, can't be that hard, eh?

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Spock Jenkins of the Vulcan Jenkins'.

Well, I guess to more accurately word my above post (as Neverfly pointed out, your DNA doesn't intelligently mutate...unless you're some cool sci-fi creature who...can, well intelligently mutate):

The fish mutate because eye-lessness has advantages; but not because they consciously know it does. A mutation will survive, and subsequently spread, only if it's not detrimental to the point where the mutated animal either cannot attract a mate, or cannot physically mate. Blindness in cave fish would cause neither. And because not having eyes would also leave one less "weak point" physically, fish with this mutation would also have a higher chance to survive, and thus better chances/more opportunity to reproduce, possibly spreading said mutation.

It's advantageous, selective evolution purely through odds and numbers, not through self awareness in mutation.

Although one could argue that the mutated animal could also be more likely to attract the member of the opposite sex due to it's advantage, which is conscious mutationism, even if the animals don't have the reasoning skills to realize it.

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I'm like one of those idiot savants...well, except for the savant part.

Theory of Zombie Relativity:
1) Everyone Else is a Zombie relative to You
2) Whether or not it matters is related to the inverse square of the distance between their teeth and your brain
(Quoted from Demigrog)

I've often heard that blind people say they can sense a wall. The report a feeling on the part of their face closest to the wall, as if they are being touched. Scientists think that what's actually happening is that their brains are sensitive enough to sound that they're able to detect echos from the wall.

The point is, without the eyes, the brain actually devotes additional processing power to other senses. So if the eyes were useless anyway because you lived in a cave, there might be a very real selective advantage to getting rid of them - beyond simply saving the resources used to grow the eye.

Agreed. But what we're also saying is that when the sperm impregnates the egg to form the new creature, the DNA doesn't go "Hmm...now what resources should I put where?" and actively chose to do away with the eyes.

What happens is that the random mutation that causes the animal to be born with no eyes does not pose any problems, and as you pointed out, may ever give an advantage to the animal. And so that animal reprodcues, and (possibly) passes on the mutation. And so those reproduce, etc. etc. And if they really do have an advantage, they should reproduce at a better rate than those without it...eventually leading to high-to-total populations of the mutated animal. Vwa-la, evolution.

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I'm like one of those idiot savants...well, except for the savant part.

Theory of Zombie Relativity:
1) Everyone Else is a Zombie relative to You
2) Whether or not it matters is related to the inverse square of the distance between their teeth and your brain
(Quoted from Demigrog)

I just posted a thread linking an article from TIME I came across today, talking about the human brain and our ability to remember the past and predict the future. The Three-Dimensional Human Mind.

Anyway, the article was about two sections of our brains: one that's active when we're thinking, and the other that's active when we're idle. According to the article, it's this idle-active section that allows us to think back to our past experiences, and also make informed guesses to our future experiences.

I'd imagine these two sections are not exclusive to humans, however are more active in humans which gives us our "intelligence" (other animals can "learn" from repeated experience, but obviously not at the same rate as us).

What's this have to do with eyeless cave fish? Well, not alot, but we were talking about evolution. If what's in the article is true, then I think we can make a pretty good bet that one of the major mutations that led to our evolution from the apes had to do with this section of our brains.

Being able to reason (ie learn from past and foresee future outcomes) would be a huge advantage as far as mating and off-spring rearing. Animals with this mutation would have lots more opportunity to survive, reproduce, and spread said mutation.

Anyway just something I thought was kind of neat.

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I'm like one of those idiot savants...well, except for the savant part.

Theory of Zombie Relativity:
1) Everyone Else is a Zombie relative to You
2) Whether or not it matters is related to the inverse square of the distance between their teeth and your brain
(Quoted from Demigrog)

The gene for "male pattern baldness" (starts at the front and progresses to the back) is found on the Y chromosome, so of course, is only found on men.

The other type of baldness is known as "non gender specific baldness". The gene for it is found on the X chromosome and therefore found in both sexes. In it, thinning starts at the crown of the head and gradually moves outward. In men (having only one X chromosome) it is fairly mild, but for women (having two X chromosomes) it can be mild or severe.

My brother has male pattern baldness (as he says - "my hairline is making a beeline for my waste line".).
I, on the other hand, have non gender specific baldness. I still have most of my hair, but it's getting mighty thin on top. That is one of the reasons I never leave home without a hat!

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Any day you wake up on "the right side of the dirt" is a good day.

T. Anderson