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ChrisRT
2004-Dec-14, 09:26 PM
I was thinking, how is it that our eyes, ears, speech, and sense of smell came along? Where, when, and why was it in the point of evolution (for those who believe in it) did these luxuries come along? Where they flukes or mutations? If so, why does everything from fish to snakes to humans and bugs have one or the other?

What is the probability that life elsewhere will have or will ever develop this?

GOURDHEAD
2004-Dec-14, 11:00 PM
I was thinking, how is it that our eyes, ears, speech, and sense of smell came along? Where, when, and why was it in the point of evolution (for those who believe in it) did these luxuries come along? Where they flukes or mutations? Evolution constantly churns the pot and tries many solutions to survival enhancement. The physical environment provided the stimuli that enhanced the survivability of critters that accidentally developed organs that gave them a decided advantage over those that did not develop such organs. The endowed critters outcompeted the others and passed the attributes on to their heirs. These attributes appeared soon after multicellulars appeared and gradually improved over time. The attributes were mutations that did not confer a disadvantage to their possessors.



What is the probability that life elsewhere will have or will ever develop this?
Very close to one. The more ways that critters can interact with their environment, the more likely they will become the dominant species in their environment and achieve a level of consciousness that supports technology.

qraal
2004-Dec-14, 11:44 PM
All living things react to their environment which is constantly impinging upon their bodies via light, chemicals and physical forces - thus senses make sense. They're not luxuries, but vital means of gaining information about the world outside one's body.

Smell is a primal sense, since even bacteria can respond to chemicals floating around in their environment. In humans it's not a lot different, but we have dedicated cells with nerves hooking into the brain - and our smell is not as efficient as in many other mammals. Taste is related to smell and touch but with not as many possible sensations - contrary to 19th century myth we don't have a "taste map" laid out on our tongues with just salt, sweet and bitter, but the range isn't as great as for smell.

Touch is the second most primal of senses and is caused by the fact that deforming the outer layers of cells changes their electrical potentials. Higher animals have nerves under their skins to pick up and co-ordinate the sense, but even single celled organisms can react to "touch".

Sight comes from the fact that most biomolecules are photoreactive and have different configurations when exposed to light - when they relax after being excited by light they give up a bit of energy that can be passed on as a signal. Initially a few light sensitive cells congregated in a certain patch on the animals skin with a few nerves to pick up the signal - as seen in flat worms. A few simple steps - simple cups and folds filled by transparent cells - and you have simple lenses which see better. Then with more curvature, more nerve cells and so on until sight improves until you have something like a fish's eye - which isn't too far removed from our own. Animals with all grades of sight, from "eyespot" to eagle's eyes are known.

Hearing is akin to touch since it depends on tiny hair cells in our inner ears. A smooth gradation from fish-style hearing to mammal-style hearing - human ears are pretty much identical to other mammals - can be seen in the fossil record. Reptiles have pretty basic inner ears that pick up vibrations in the bones near them, then between reptiles and mammals the various jaw bones around the ear became more and more involved in hearing while the dentary bone expanded and became the only lower jaw bone.

Other senses exist - chemical senses separate to smell, electrical senses, gravitational senses [balance is a sixth sense], and you could make a case for other "senses" based on reasoning and cognition.

ChromeStar
2004-Dec-18, 03:41 PM
Hi ChrisRT

QUOTE
I was thinking, how is it that our eyes, ears, speech, and sense of smell came along? Where, when, and why was it in the point of evolution (for those who believe in it) did these luxuries come along? Where they flukes or mutations? If so, why does everything from fish to snakes to humans and bugs have one or the other?

Evolution is the process of elimination of creatures with features useless or inhibiting of there environment. so obviously - based on evolution - creatures will retain features like sight, hearing etc with exception to creatures not needing certain features i.e. no/little sight in moles. On earth most creatures have these commonalities because they are usefull.

QUOTE
What is the probability that life elsewhere will have or will ever develop this

The chances are good relitive to the creatures environment

Ola D.
2004-Dec-22, 08:08 PM
Originally posted by ChrisRT@Dec 14 2004, 09:26 PM
I was thinking, how is it that our eyes, ears, speech, and sense of smell came along?
Sight, hearing and sensitivity have centres in the brain responsible for detection, stimulation and response. Nerve endings connecting these organs (eyes, ears, skin.. etc.) with the brain are responsible for conducting impulses at a very high speed.


If so, why does everything from fish to snakes to humans and bugs have one or the other?

Because irratibility, stimulation and reacting to the external surrounding is an essential characteristic of all living things.

downunder
2004-Dec-23, 02:48 AM
Most of these senses will only evolve in life that's mobile. Which is why you rarely find a flower with eyes :) Off the top of my head the only plantlife I can think of that's developed any of these senses are the carnivorous plants like a venus flytrap which relies on a primitive sense of touch so it can close up and trap any insect that wanders into it.

Ola D.
2004-Dec-24, 10:55 AM
Originally posted by downunder@Dec 23 2004, 02:48 AM
Which is why you rarely find a flower with eyes :)
Yes true, but plants also have reactions coordinated by hormones as a response to the different enviromental conditions it experiences. For instance, auxin enhances phototropism, so that to curve the stem in any direction to be exposed to the highest light intensity for photosynthesis. Another examples are hormones inducing seeds dormancy, fruit development... etc.

Nereid
2005-Jan-12, 07:00 PM
No one seems to have yet answered the 'when' question, so here's one go:

There's essentially no data to guide us as to when the 'chemical' senses first appeared; the fossil bacteria don't retain enough of anything much to give much except hints. Possibly some form of these evolved way before the earliest record of life on Earth; if so, it would seem there's no way to tell when.

Ditto for gravity (up-down) and light (but NOT sight). The fossil stromalites suggest that both these would be necessary, so that puts at least these two as far back as several billion years.

The sense of touch probably needs to be better defined; maybe all multi-cellular organisms have this? If so, then it evolved in the Pre-Cambrian, possibly as long ago as 1 billion years (or even longer).

Sight may have arisen with a bang ... at least one researcher has a strong case that the 'Cambrian explosion' was due to the development of the sense of sight. That's ~550 mya.

Magnetism? IIRC, there are bacteria which can sense a magnetic field, but I don't recall whether there's a fossil record of those types.

The separation of taste and smell would seem to require multi-cellular organisms, and animals at that. If the distinction between the two involves air-born vs in (water) solution, then fossils of the first land animals should show how quickly the two senses became two.

Electrical? How could you tell, from a fossil?