Origin of Reflexes and Instincts

[blike]

How are reflexes and instincts theorized to have evolved? For instance, babies automatically hold their breath when they're submerge (though they still swallow). Under what circumstances could this behavior be genetically programmed and screened for? Lets assume, for instance, a race of primitive humans exists where babies don't hold their breath when submerged. The amount of babies who would fall in the water unsupervised is very very small. Now we have to assume that some genetic mutation causes babies to hold their breath under the water. Firstly, how does a genetic mutation cause changes in instinct? I assume the mutation changes the structure of the brain. This is quite a stretch though (at least in my view). A lot of things have to change in sequence for this behavior to be exhibited. Second, assuming this mutation DID occur, the advantage would be so negligible that it would not effect survival rates enough for it to be selected for..

 

Any thoughts?

[fafalone]

Now they don't fall in the water... but our predecessors might have. And of course evolution happens over thousands of generations. It's definately not a disadvantage, so its advantage over time and numbers became dominant.

 

Instincts are genetic.

[DocBill]

Babies can swallow WHILE they breathe. For a real explanation of this, look into the Aquatic Ape Theory by Alistar Hardy; and Borcca's Brain by Carl Sagan.

 

Bill

[Skye]

I might be wrong here because this is all off the top of my head and I'm in a hurry.... but it would seem rather favourable to hold your breath whilst being born. Either way voluntary control of breathing isn't the norm in the animal world nor is a trachea leading up to your mouth (rather than nose.) Babies have their trachea leading to their nose though so it might be a carry over.

 

Realistically I think it should be a wading ape theory, I don't think it's proposed we were ever sea monkeys.

[Glider]

If it was true that babies have their trachea leading to their nose rather than their mouth, then the first scream they produce on birth would be through their nose, not their mouth, nor would they cough through their mouths when they choke on milk, or choke on milk in the first place. Horses have separate trachea/oesophegus and can swallow and breathe at the same time (as can many similar animals). This is helped by the fact that the trachea in horses and many other animals lies behind the oesophegus, rather than in front of it (as it is in humans). Humans have the epiglotis which closes (reflexively) over the trachea when we swallow. However, all animals will stop breathing on immersion. This is reflexive. In human infants, the epiglotis closes by reflex and the ability to swim (orient and propel themselves to the surface) is instinctive (and is lost after about 6 months and has to be re-learned).

 

Reflexes are simple afferent/efferent loops (e.g. the spinal reflex arc mediating limb withdrawal on exposure to noxious stimuli) and are usually self contained functional units. Instincts are similar, in that they are hard-wired, but are much more complex. The things that define instinctive behaviours is that they are behaviours which do not require any learning, and are universal within the particular species. For example, the ability of a newborn animal to locate its mother's teat. Humans have this instinctive behaviour, but its based on a reflex (the rooting reflex). If you stroke the cheek of a newborn infant with your finger, it will open its mouth and orient its head towards the stimulus. This serves a useful purpose to the infant as the usual position the mother holds it in is across her front, therefore the most probable thing to stimulate the cheek of the infant will be her teat (food!). Reflexes and insticts are closeley related (the latter often based on the former), and differ mainly in deree of complexity. Both evolved as advantagious patterns of behaviour; certain actions or 'routines' that provide the organism with a survival advantage (i.e. finding food quickly after birth, not drowning, etc.).

[Radical Edward]

Originally posted by Glider

This is reflexive. In human infants, the epiglotis closes by reflex and the ability to swim (orient and propel themselves to the surface) is instinctive (and is lost after about 6 months and has to be re-learned).

 

I've heard about these things, for example, babies "walk" ability, that again is lost and has to be relearned. Are these things just lost through lack of practise then? for example, are babies who are exposed to water from a very young age able to learn to swin more easily?

[Skye]

Man I was wrong:D though I did give you fair warning.

 

Babies also extend their toes out when you rub the bottom of their feet. Supposedly this reflex can return when people are drunk, which sounds fun to me. Oh and putting their hand in a glass of water. That's just evil.

[Glider]

Originally posted by Skye

Man I was wrong:D though I did give you fair warning.

Nah..that's fair enough. It's a common belief that babies can swallow and breathe, and you can see where it comes from given that once 'attached' they don't tend to let go till they're full.

 

Babies also extend their toes out when you rub the bottom of their feet. Supposedly this reflex can return when people are drunk, which sounds fun to me. Oh and putting their hand in a glass of water. That's just evil.

Heehee...ain't it though?

 

This is quite right. The thing with the early reflexes (like the Babinski sign you mention above) is that they never really go...they're just supplanted by later (cortical) developments. One of the signs of damage to higher centres (e.g. a sub-dural bleed or something) is the return of these early reflexes. Because of this, you'll often see medics checking for these reflexes when people are admitted with head trauma. Enough alcohol will supress the higher centres so that these reflexes return. Sounds like a Friday night experiment to me (just to make sure it's still the case, you understand )....yay!

[Glider]

Originally posted by Radical Edward

I've heard about these things, for example, babies "walk" ability, that again is lost and has to be relearned. Are these things just lost through lack of practise then? for example, are babies who are exposed to water from a very young age able to learn to swin more easily?

Yep, partly through lack of practice, but that's understandable. The babies 'walk' reflex is apparent at an age when they can't physically support their own weight with their legs, so practice is a bit out of the question.

 

With the swimming thing though, if (as some people do) you take the baby swimming weekly, then the reflex is never lost and the behaviour (and required patterns of motor function) is reinforced and incorporated into the developing higher centres that deal with that activity. So, in effect, the baby never has to learn how to swim, it's simply not allowed to forget in the first place.

 

The same thing goes with walking, but it's a bit more risky as babies leg bones and pelvis are not sufficiently developed (you must have seen the angle at which babies' legs stick out laterally, like chimps), so walking a baby up and down would risk impeding or harming normal leg and pelvis development, and, as they would have to be supported, wouldn't necessarily allow them to learn balance anyway.