Evolving Senses

[Lestat]

Warning: This post has idiot rambling and some very dumb questions. Feel free to flame my stupidity, but please have the class to at least provide me with some insight.

I often wonder how we evolved to have the senses that we have. To me, it's quite remarkable that we have eyes to see the world, and ears to hear sounds. I suppose I can imagine how we developed the sense of taste. It makes sense that when an organism ingests something which can kill or harm it, it would evolve a distate for it. Likewise, when something is healthy, we would devolop a pleasing sense (although I'm not sure how this explains why in today's world almost everything that tastes good to me, is unhealthy -lol). In addition, I understand how other poisenous living things evolved to taste bad so that others wouldn't eat it. So ok, to a childlike degree I guess I understand a little (but it's probably still very wrong).

But the eye... That has to be one of the most amazing evolutionary inventions. What evolutionary pressure could've been put on an organism that would a). Allow an organism's genes to realize that visual sight was even possible, and b). To then select for it?

Aren't plants and trees among the only organisms that don't have sight? All other organisms that do not employ sight live in places where visual sight is impossible (or not very practical, such as the bottom of the see, or underground, or those that dwell in the darkness of night).

So what was it about light that tipped off a gene that sight was even possible, let alone beneficial?

Again, I'm willingly showing my ignorance and incompetence to gain even a little insight to better understanding this. Thanks.

[Taraz]

Actually many plants can "see" light and shift toward it. I realize they don't have eyes, but they can react to light and move.

It seems like something similar could have happened at the outset of animal vision. First it was simple reactivity to light and dark, and then to different wavelengths of light, and then to specific boundaries in the source of the light (edge detection), etc.

[Arp220]

Many cells are light sensitive, just by virtue of basic biology (which I know little about, to be fair)

Then just add in that sudden changes in light levels usually presage being eaten by something big.... and you get an evolutionary driver for more and better light sensitive cells [img]/images/graemlins/smile.gif[/img]

[Aver-aging]

[ QUOTE ]
Actually many plants can "see" light and shift toward it. I realize they don't have eyes, but they can react to light and move.

It seems like something similar could have happened at the outset of animal vision. First it was simple reactivity to light and dark, and then to different wavelengths of light, and then to specific boundaries in the source of the light (edge detection), etc.

[/ QUOTE ]

That's pretty much it. There are tons of animals and cells out there that have 'light sensitive' areas that influence them to move towards lit areas. *EDIT* Considering that prehistoric bacteria were factories for photosynthesis, it is no surprise that having a sensory organ that attracted it to light became a huge advantage. It all started out with that, but it evolved because other necessary pieces of equipment evolved with it.

The most important thing to remember about mammalian senses is that they evolved along with the development of the cortex in the brain. Our sensory organs just provide us with a means of obtaining sensory information, and their evolution will always be limited to the capacity that our neocortex has for deciphering that sensory information and creating recognizable and understandable patterns with it. So these organs kind of always evolved at the same rate neocortex evolved at.

And Lestat, the reason why lots of those unhealthy foods taste good is because back in the old days (pre-human and early human days) our ancestors had to work hard for their food, and evolved to love foods that had loads of sugar and fat in them for energy. Our bodies are built to adore calories.

[gumpzilla]

Dawkins wrote a book focusing on exactly this line of thinking. It's called "Climbing Mount Improbable" and is a quite interesting read. I don't remember all of it, but the chapter on the eye makes what I thought was a pretty compelling case (when I read it a few years ago) for how gradual development of the modern eye could have taken place.

EDIT: He also discusses wings, which seem sort of like another "all or nothing" type development you wouldn't expect from evolution, and how they could have occurred. The final chapter was a very weird symbiotic relationship between figs and fig wasps that I wish I remembered better.

[carlo]

The eye is formed in response to the light.Light first, then the eye. Consider a primeval light "burning" a hole within the human body, that of severe pain. In response to the pain an organ which lives in the pain is formed and is called the eye. One gains a sense of the light through this evolutionary movement. Note that the eye is practically disjointed from the human body, in its own sockets. It almost seems that one could remove the eye as it appears to be part of external nature. Our other senses are more inward but the principle is the same, outer sensibility to inner senses.

Should state that the "human body" was is no way alike to our present body. Think ethereal and you still won't have it.

[vhawk01]

[ QUOTE ]
The eye is formed in response to the light.Light first, then the eye. Consider a primeval light "burning" a hole within the human body, that of severe pain. In response to the pain an organ which lives in the pain is formed and is called the eye. One gains a sense of the light through this evolutionary movement. Note that the eye is practically disjointed from the human body, in its own sockets. It almost seems that one could remove the eye as it appears to be part of external nature. Our other senses are more inward but the principle is the same, outer sensibility to inner senses.

[/ QUOTE ]

You might be the greatest 17th century scientist to ever live, or at least you could write some mean books for those guys.

[carlo]

[ QUOTE ]
The eye is formed in response to the light.Light first, then the eye. Consider a primeval light "burning" a hole within the human body, that of severe pain. In response to the pain an organ which lives in the pain is formed and is called the eye. One gains a sense of the light through this evolutionary movement. Note that the eye is practically disjointed from the human body, in its own sockets. It almost seems that one could remove the eye as it appears to be part of external nature. Our other senses are more inward but the principle is the same, outer sensibility to inner senses.



You might be the greatest 17th century scientist to ever live, or at least you could write some mean books for those guys.


[/ QUOTE ]

Think deep Hawk, and then go deeper, but of course you're going to get wet. Are you and Midge comparing notes? He has me in the coffee houses at the end of the 19th century. You're in regression. [img]/images/graemlins/grin.gif[/img] Please note my addition to my original post, it might clarify, maybe.

[Lestat]

Thanks to everyone for their responses. They were more insightful than I had hoped. Aver-aging, you seem to have far more than an average layman's knowledge of this. Thanks. Much of what you stated let's me make better sense of the eye.

Also, thanks to gumpzilla. I'll have to read, "Mount Improbable". I've heard of it, but have been too lazy to buy and read it. I'm encouraged to do so now.

I'm still a little slow on this though. While I can comprehend a cell being sensitive to light, and moving towards light (I understand this, because it makes sense how this might be beneficial to an organism), I still don't get how a cell can go from sensing light, to picking out the intricate details in a leaf for example.

Well, I guess I can imagine it, but why? There's a whole world we never would've known about if we couldn't see if we didn't developed the sense to experience it. Can we go on to hearing?

So there was a time when an organism could sense sound because the ground shook due to a loud noise. Over time, what happened? That sound started being sensed more and more intimately by certain cells until it could actually hear all sorts of different wavelengths?

I think this whole subject is fascinating. How a cell went from sensing light or sound, to develop more cells to pick up all the fine details of it. I wrote a post a while back on how many things are out there that we do not have the ability to sense. I suppose there are quite a lot, like UV and gamma rays, etc. Oh, and...

I just read that scientists think they discovered that birds can actually see magnetic fields! That's literally see with their eyes. Until now, it was thought they could only sense them through some sort of internal compass. Yes, evolution is amazing!