Light sensitive skin?

Why do albino chidren occur without rhyme or reason. Another gift from god

No

worthy,

I believe I know where you are going with this.. Now, I can probably help explain, but first I will need you to tell me what is meant by "light sensitive skin" --- i.e. in what way does the skin respond to light?

The way you have presented it, the "skin" is the only thing sensitive to the light (meaning the dermal tissue, not the nerve tissue within it) -- and the sensitivity does not appear to be the type that we talk about when we say a person sunburns easily. If that is the case - if the cells have some unusual behavior that acts in a way that is isolated from other organs of the body, it is quite possible that there would be no selective advantage or disadvantage to this trait & it would be unlikely to become fixed in the population.

If you had something else in mind though, I could perhaps explain the mechanism of selection in regards to it if I had more detail on what you meant...

 

Do you need to "know" how to metabolize your food in order for your body to use it? Do you even need to be aware that you are eating? A simple organism is not aware of its own existance, let alone its biochemical processes. Knowledge has nothing to do with survival.

Having light sensitive skin is not necessarily enough to ensure the survival of an organism. Unless that light sensitivity results in a change in behaviour.

Unworthyone,

You have many issues here and I will address them out of order.

Then how does this trait get passed along to its kids if its mate does not have the genetic mutation of light sensitive skin?

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If the trait is the result of a genetic mutation, then it can be passed on. However, this can only happen if the mutation is also found in the germ line of the fish.

how this light sensitive skin is recognized as a "trait" that would improve survival

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If the trait improves the fish's ability to reproduce over non-sensitive skined fish, then it would carry a selective advantage. If it decreases the ability to reproduce, then it would be disadvantageous. If the ability to reproduce is not affected at all, then it would be a neutral trait.

and how the body knows it now has light sensitive skin.

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It doesn't, no more then my body "knows" that I have brown hair.

What use is light sensitive skin if the brain of the organism doesn't even know it has it?

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In other words, you are asking what happens if the fish can't "see" with light sensitive skin. Well in that case then nothing happens. If the skin is light sensitive, but the fish is unable to "sense" with it, then it probably will be a neutral trait.

unworthyone: Now guys, pretend I'm an idiot (which you probably already do)...

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Actually, you're asking questions, so I have a hard time thinking of you as an idiot.  Idiots already know it all. 

unworthyone: ...and explain, maybe metaphorically, with some imagery or something, how this light sensitive skin is recognized as a "trait" that would improve survival and how the body knows it now has light sensitive skin. What use is light sensitive skin if the brain of the organism doesn't even know it has it?

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Well, that's what nervous system handles in organisms--taking all the various inputs and outputs and using them.  I can't speak to organisms simple enough not to have one--I'm not a biologist--but in organisms with nervous systems, they are able to take inputs and feedback and learn how to use the various bits they have.  Leech neurons, for example, have been used to control robots by giving them stimulus and feedback; eventually the neuron clusters are able to learn the behavior the scientists wanted via a photocell input.

Thus, in your example, the organism would have an extra bit of input, and would have to learn how to use it.

unworthyone: Then how does this trait get passed along to its kids if its mate does not have the genetic mutation of light sensitive skin?

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You know, it's been way too long since I had my biology courses, and I haven't read much on this, so my knowledge on genetics is a little lacking, so I could be a bit off here.  When a child organism is formed (from species that have genders, I forget the term), it gets some of its genetic material from both parents.  The mutation for the light sensitive skin--or something mutated even futher--may be present from the mutant parent's contribution.  There's more than this, but someone like Rufus might better be able to explain this.

Ok, worthy...

Let's talk about two paths this evolution of the eye could have taken. The first is "light sensitive skin", but here we would have to consider the possibility that the light sensitivity was in nerve endings that were already connected to the brain of the organism. For this to confer a selective advantage, then the behavioral response to the activity of these nerves would have to be one that was more advantageous in the presence of light.

The other possibility is that single-celled organisms, or extremely simple multi-celled organisms became sensitive to light. The response might not be a result of a central nervous system, but a direct response (motion, for instance) by the cell(s) affected. If that motion is advantageous in the presence of light, it could be selected for --- and the genes for light-sensitivity may have been passed down from those cells to the more complex multicellular life that came later, where those genes may have been only expressed in cells of the emerging nervous system.... For instance, a single celled organism swims "towards" light: it is rewarded by water nearer the surface and richer in oxygen. A colony of light-loving cells is established, and eventually simple multicellularity evolves. Then specialization of tissue begins to evolve, and the genes for light-sensitivity are only "switched on" in the tissues where they have a positive impact on survival, and "switched off" elsewhere as a conservation measure.

As to how this trait is passed on, that would depend on the scenario. In organisms that reproduce by mitosis and fission, the obvious answer is that each daughter cell carries exactly the genome of its parent cell.

In organisms that reproduce sexually, then there is a certain probability (depending on the number of offspring that the organism produces in one lifespan) that the trait will be passed to the second generation, where one or more of the daughter organisms will be heterozygous for it. They in turn each have a chance to pass it to the third generation, etc... It is not entirely unlikely in a small breeding population that an organism could be homozygous for the trait by the third generation (if its parents were brother and sister). On the other hand, it may confer its advantage only when expressed heterozygously (see sickle-cell anemia), in which case, just the possession of one copy would be enough increase the chances that the next generation will carry the gene. If it is a trait that depends on being carried homozygously for advantage, then there is a time before the gene has enough currency in the population that we have to hold our breath & see whether the gene will survive long enough to become subject to selection.

I guess I have been completely unclear in my response & while I was typing it most likely everyone else has piped in with a better answer than mine, but there you have it.

Worthy,...
Rufus said:

In other words, you are asking what happens if the fish can't "see" with light sensitive skin. Well in that case then nothing happens. If the skin is light sensitive, but the fish is unable to "sense" with it, then it probably will be a neutral trait.

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Selectively neutral mutations do not tend to persist in a population so long as that. Sometimes they do come about as a "pre-adaptation" which becomes useful generations later when the environmental factors are right, but they do not tend to lay latent while whole other systems evolve to incorporate them. I don't think that he sees the likelihood of something very complex evolving from an adaptation like light-sensitivity that has no behavioural impact. I think he was just answering your question - not jumping ahead to the question of how eyes evolved.

Originally posted by unworthyone
Ok, from quite of few guys over here I've learned that populations evolve not individual organism, animals etc..

So lets say we have 10,000 sightless water organisms and one of them, through genetic mutation, gets blessed with light sensitive skin.

Now guys, pretend I'm an idiot (which you probably already do) and explain, maybe metaphorically, with some imagery or something, how this light sensitive skin is recognized as a "trait" that would improve survival and how the body knows it now has light sensitive skin. What use is light sensitive skin if the brain of the organism doesn't even know it has it? Then how does this trait get passed along to its kids if its mate does not have the genetic mutation of light sensitive skin?

Can someone help me understand this?

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OK, we have to go no further than the paramecium.  Not even multicellular, but has a light-sensitive spot.  Connected to the cilia such that the paramecium can move toward greater light -- which is where the concentration of bacteria that it feeds upon comes is at!

Now, as to getting passed on.  Let's see if we can reason it out. Let's assume, for simplicity, that the light sensitive allele is L.  Let's even assume, for simplicity, that the female doesn't have one (and yes, the paramecium does reproduce sexually sometimes).   So, the paramecium has LL in it's two DNA strands.  The mate is -- because it has no gene for L.  The two paramecium merge and undergo sexual recombination, where they exchange genes.  So now both offspring are now L- and L-.  One allele from the L parent and one blank allele.  Of course, as soon as the DNA is copied, the L will be copied also and you now have LL.

Originally posted by unworthyone
So this mutation had to be present in the other fish, or in the germ line of its mate? Do you have diagram or can you make one on this?
Is that how we must assume it worked? And then later in time the population of fish, with this light sensitive skin, began to form neural connectors to it? Or for the fish to even form the light sensitive characteristic must it already be neurally connected?

Would these fish all look the same at glance, but the ones with the light sensitive skin may have like a small discoloration of some sort on its skin? 

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No, the mutation didn't have to be present in the other fish. 

Again, let's start out with a fish that has a gene "l".  This gene undergoes a mutation to become L.  And L gives a light sensitive spot (didn't happen that way, since fish descended from ancestors that already had eyes, but this is just an example).  So now the fish has L on one strand of it's DNA and l on the other strand.  Now, in meiosis to form a sperm (assuming this is a  male fish), you end up with a sperm with L and a sperm with l.  Now you get to combine with a female fish's egg.  This egg will be l because it doesn't have the mutation.  So have the female eggs fertilized will be Ll and half will be ll.  BUT, at this point selection intervenes and let's be drastic -- only the Ll fish survive.  So the two fish had 10 offspring, 5 with Ll and 5 with ll.  But only the 5 Ll survive. Each breeds and produces 10 kids.  That's 50 total offspring. Since it is unlikely they bred with each other, that means 25 fish with Ll and 25 with ll in the second generation of this population. Again, only the Ll survive.  Next generation, assuming no interbreeding with 1st cousins, we end up with 125 Ll fish in that generation.  Now, let's say that 2nd cousins start interbreeding.  Ll and Ll give you 25% of the offspring with LL, 50% of the offspring with Ll, and 25% with ll.  Say 10 of the 125 Ll fish interbred for 100 offspring. That's 25 LL, 50 Ll, and 25 ll.  Only those 75 having L survive.  So, let's just look at the LL's.  Say they breed now with a ll.  All 25 of them will produce LL kids,

This is a simplified example, but do you see how fast such a mutation will spread in the population until every individual will have it, even if it happened only to one individual.

Now, we assumed the most drastic selection for simplicity.  However, it works just as well as long as there is any selection.  It just takes more generations but the result is the same.

Originally posted by unworthyone
Now guys, pretend I'm an idiot (which you probably already do) and explain, maybe metaphorically, with some imagery or something, how this light sensitive skin is recognized as a "trait" that would improve survival and how the body knows it now has light sensitive skin. What use is light sensitive skin if the brain of the organism doesn't even know it has it? Then how does this trait get passed along to its kids if its mate does not have the genetic mutation of light sensitive skin?

Can someone help me understand this?

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My question to you: Does the organism have to know it has a mutation in order to gain an advantage from it?

Try this analogy:By some genetic fluke, you were born with an incredibly strong immune system. You've had it your whole life, but never knew about it. This is a beneficial mutation.

Now let's change the environment: Let's suppose that someday, a terrible plague sweeps across the world. Almost the entire planet is wiped out. Your mutated immune system protected you, although you didn't know it. You'd think it was God, minimal exposure, or just good luck.

You, and a handful of other humans with similarly mutated immune systems, will survive and eventually repopulate the planet. Those children will have super immune systems too, as will their children, etc......

And there you have it. You caused an evolutionary leap in the human race and never suspected it for a moment.