Eyes

[Believer112]

So, your saying evolution has an intelligence? These RNA, DNA. amino acids ect... all decided it was advantages to create an eye? How did they know what an eye was to begin with?

The short answer is that eyes are advantageous and you can get eyes through mutation and natural selection.

If you can see when a predator comes your way, for example, you have a better chance of not becoming someone else's dinner. The most primitive eye on probably was only able to detect the presence of light and possibly the wavelength/color - jellyfish for example can only do pretty much that. They use that information to decide whether or not to become docile or energetic as different light has a profound impact on their enviornment.

[LuftWaffle]

D-9,

The short answer is that eyes are advantageous and you can get eyes through mutation and natural selection.

Is there any possible organ that you can't get through mutation and natural selection?

[MorningGlory]

D-9,

The short answer is that eyes are advantageous and you can get eyes through mutation and natural selection.

Is there any possible organ that you can't get through mutation and natural selection?

A brain.....?

[nebula]

For multi-celled, it probably started with a patch of epithelial cells becoming light sensitive.

Epithelial tissue became nervous tissue?

That's a good jump.

From what I understand a light sensitive cell needs a photoreceptor to acknowledge the light, and another molecule to start signal transduction to nerve fibers. As you probably know, we start off as a zygote which then undergoes mitosis to create us. In that process cells undergo cell differentiation, so despite that our epithelial and nervous cells have the exact same DNA, it is expressed differently and that expression is usually the result of our development from zygote to baby. Change the development and you get profound effects. I do not think it is as hard to go from epithelial cells to light sensitive cells as you make it out to be once you start messing with development.

I'm not referring to fetal development. I'm talking about "evolution."

Epithelial tissue and nervous tissue are incredibly different from each other - different shapes, different physiology.

For an epithelial cell to be light sensitive, it would take both an anatomical and physiological change.

That's a significant jump for a mutation.

[Believer112]

Having an eye or eyespot is advantageous because of what it does in said environment, not because anything decided that it was advantageous.

How did the primordal soup determine; because of the enviorment, that every animal on this planet would need eyes.

Hebrews 11

Faith in Action

¹ Now faith is confidence in what we hope for and assurance about what we do not see. ² This is what the ancients were commended for. ³ By faith we understand that the universe was formed at God’s command, so that what is seen was not made out of what was visible.

[nebula]

I'm not referring to fetal development. I'm talking about "evolution."

Epithelial tissue and nervous tissue are incredibly different from each other - different shapes, different physiology.

For an epithelial cell to be light sensitive, it would take both an anatomical and physiological change.

That's a significant jump for a mutation.

Evolution and development are intricately intertwined.

How so?

In the case of development, the DNA codes are in the cells, waiting for the "on" signals to determine the next step.

In the case of evolution, the DNA has to be either mutated or added to or reprogrammed or new commands that didn't exist before need to come to be somehow.

That's a huge difference!

Cells in the early developmental stages are omnipotent (able to develop into any type of cell within the body).

"Omnipotent"? Cells are "all knowing"?

All-differentiating, yes, in the initial totipotent phase anyway. But not "knowing". That makes it sound like there's a brain behind it.

The same type of initial cell developing into a skin cell, a nerve cell, a liver cell, and so on happens everyday. Genetic changes that affect development can have far reaching effects.

Does the creation of something that never existed before, though, happen every day?

Skin cells were pre-programmed. Nerve cells were pre-programmed. Liver cells were pre-programmed.

Potorecptors on an organism that never had photoreceptors before is not the same as a liver cell having an altered function, for example. That would be like a baby being born with liver cells that can sense internal heat, or something like that.

[nebula]

The first 'eyes' would have been eye spots on single-celled organisms.

How do "eye spots" function on a single-celled organism without the eye spot being a nerve cell of sorts?

I don't know, the eye spot is an organelle and we see it today in organisms like the Euglena. I don't know how it works, I just know that it does and we can see it today.

The best I can see is that the "eyespot" is simply a light receptor that allows the organism to turn itself towards or away from the light, useful to the Euglena because it carries out photosynthesis.

Some sources all it an organellle, others a cell.

Weird.

If it's a cell, than the organism isn't single-celled anymore!

[nebula]

I need to give some background to my line of thinking.

Tissues are divided into 4 types: epithelial, connective, nervous, and muscular.

Epithelial tissues are for protection (protective lining), secretion, absorption, diffusion. Their structure assists their function.

Nervous tissue is for communicating information. To do so involves a complex interaction between ions across the plasma membrane - which involves the addition of structures for the function.

To go from an epithelial cell to a nervous cell (photoreceptor) would take more than a little mutation.

[nebula]

A lot of the evolutionary change is expressed during fetal development - how long and when certain processes are doing their thing during development have profound impacts on development. Change the course of development (which can/is inherited) and you can get big differences.

OK, then would you please give an example of an observed change? One that created something completely new like this?

You aren't really changing one cell type to another type of cell, you are changing the developmental pathway of certain cells before they differentiate.

Did you read my last post? There are a lot of differences between an epithelial cell and a nerve cell. Nerve cells require the ability to produce and action potential, and that requires the inside of the cell membrane to have a specific "resting potential" charge, ion channels, additional or formation of NA-Cl pumps, and enough sodium and potassium for the action potential to be generated down the plasma membrane.

Nerve cells are likewise different in their organelle make-up from epithelial cells.

Can all of this organization take place in some early embryonic mutation?

[LuftWaffle]

D-9,

Is there any possible organ that you can't get through mutation and natural selection?

I do not think any organ that is present today could not have evolved.

So, no matter what you find in nature, if it exists, it can be explained by mutation and natural selection? Where does that leave us concerning prediction and falsification? You've said that no existing organ cannot be explained by mutation and natural selection, so then any organ that exists can be explained. The only things then that cannot be explained are things that also do not exist. What then does evolution predict?

Secondly when you say you think there isn't any organ today that could not have evolved, what do you base this on, since nobody have ever witnessed even a single organ coming about through this process? You've also stated that, " Just because scientists don't yet know how something evolved doesn't mean that it didn't.", which means that evolution is believed to have produced these organs without any knowledge of 'How'. In other words evolution is assumed a priori, based on faith.

Edited February 22, 2011 by LuftWaffle