The sense of touch

[ezragray]

At the risk of sounding simplistic, I wonder how old one could say each human sense is, evolutionarily speaking. I've read that the first sign of what could be called an eye appeared 550 million years ago but what could be said for the other 5 senses? I've read that hearing is in many ways an extension of the sense of touch, and its well known that smell and taste are conflated senses. Could this be the case for other senses (one being and extension of another)? How old could we say the sense of touch is? Assuming it to be a more basic sense, how basic (or old) could a lifeform and still experiencing what we call touch?

I'd love to hear any theories on the subject. Thank you.

 

Edited February 12, 2018 by ezragray
clarification

[Bender]

We have a lot of senses of touch:

- four different pressure senses

- sense of cold and heat

- sense of pain

- hair follicles 

- proprioception, the sense of position and force in our limbs, which is itself a collection of senses.

 

I guess it must be almost as old as multicellular life, since they are required for coordinated motion. Some, such as temperature, perhaps older.

 I would expect smell/taste to be the oldest sense.

[ezragray]

Could one attempt to place each of the six human senses as they emerged through evolution in a chronological order or would that be over simplifying the process? If scientists consider smell/taste, and touch (touch in its earliest form) as more basic or primeval senses, then would sight and hearing by emerging later be considered more sophisticated or underdeveloped(younger) in comparison?

[Bender]

That would be pretty simplistic indeed. Even bacteria can react to light (see), chemicals (taste/smell) and touch. Hearing is basically sensing vibrations, which plants can do.

So all senses in some form are almost as old as life itself, and developed simultaneously as cells specialised in multicellular organisms.

[Ken Fabian]

On 13/02/2018 at 8:17 AM, ezragray said:

At the risk of sounding simplistic, I wonder how old one could say each human sense is, evolutionarily speaking. I've read that the first sign of what could be called an eye appeared 550 million years ago but what could be said for the other 5 senses? I've read that hearing is in many ways an extension of the sense of touch, and its well known that smell and taste are conflated senses. Could this be the case for other senses (one being and extension of another)? How old could we say the sense of touch is? Assuming it to be a more basic sense, how basic (or old) could a lifeform and still experiencing what we call touch?

I'd love to hear any theories on the subject. Thank you.

 

 

Touch is a mixture of different sensations felt by different means - pressure, vibration, heat, cold etc. As is too often the case the sensory function of hairs get no specific mention in the "map" of relative skin sensitivity - yet W.Montagna ("Evolution of Human Skin", 1985) pointed out that in humans their nerve rich follicles make them "the principle anatomical unit of skin sensibility". Sensitivity of skin has most often been measured by means like poking the skin with thin rods - but the poking method tends to bypass the hairs. My own experience tells me bugs small enough to not be felt on truly glabrous (hairless) skin can often be easily felt via hairs as they bump the hair shafts. ie hairs provide a lower minimum threshold for detection than direct contact with skin. (sorry, this is a bit off-topic but the "body hair is a useless evolutionary leftover" claim is a commonplace myth that irritates me, most especially when it quietly makes it's way into scientific studies as an underlying assumption, such as when assessing and measuring skin sensitivity. I'd be interested to know how they did the measuring behind this graphic, but I strongly suspect it was by means that did not assess the hairs/follicles contribution. As another example - this school level experiment for assessing skin sensitivity actually begins by removing the hairs!)

How old is the sense of touch? I don't know but it seems to have arisen very early within early animals, so as long as that. The ability to respond to touch doesn't appear to require a nervous system; micro-organisms of various kinds that lack nerves seem to, as do some plants such as Venus Fly Traps. The pathways in microorganisms may be biochemical - perhaps they are a combination of touch and taste.

Edited February 15, 2018 by Ken Fabian