This Idea was conjured from a recent thread. It pertains to the Mammalian dive reflex. This is a question for the scientists and evolutionists and philosophers out there…
Basically, the Mammalian Dive Reflex is a reflex that all mammals have. It has some actual utility among cetacians and pinnipeds or (whales/dolphins and seals/sealions) This reflex allows mammals to hold thier breath and efficiently distribut oxygen around there brain for upwards of an hour to two hours. Two hours only on older more experienced animals. The oxygenated blood actually does not feed the limbs and extremeties like while normally breathing, instead the blood is re-directed if you will, to feed the brain and major organs. Heart-rate slows down etc…etc…THIS can also be seen in humans, for instance, when you hear of someone falling in a frozen lake and drowning then being pulled out after an hour, and living! Thats the mammalian dive reflex at work in humans…
Question: (A) Why would a species like homo-sapien, or any land dwelling mammal, have a reflex such as this one?
(B) Did mammals truly come from the sea?
Actually being pulled out of a frozen lake and revived is an example of refrigeration, not the mammalian dive reflex.
A. It is questionable to the point of being highly doubtful that humans posess this reflex. Submergence in water of any death will result in pressure on the outside of the outside of the body because of the liquids and spaces inside not being fully gas saturated at that depth. The net effect is reduced circulatory activity at the surfaces and extremeties. This is a matter of pure physics, though some mistakenly argue that it is a result of the vestigial dive reflex. Unless a water filled sealed plastic bag also posesses a dive reflex, these people are mistaken.
B. Yes. Us mammals have been evolving for a long time in a wide variety of environments. Ultimately all life came from the sea. Our ancestors have been land dwellers, and at least partial if not full sea dwellers several times over in the course of a billion or so years of evolution.
Actually it is both. The mammalian dive reflex is not questionable, it exists to some degree in all humans. When your face is exposed to cold water your heart rate, metabolism, etc. will drop. Try it yourself. Take your resting heart rate. Try to hold your breath as long as possible. Now wait for your heart rate to normalize again (it will rise if you hold your breath). Now go stick your face in a bucket of ice water. See how long you can hold your breath. Take your heart rate again. Your breath holding time will increase and your heart rate will drop. I did this last fall in my E-Care (EMT-B standard of care medical class) and my breath-hold time rose from 1:07 to 1:52 with no other training and my heart rate dropped from around 84 (my normal resting rate) to 60. We did this to demonstrate the importance of attempting recessitation upon drowning victims up to an hour and a half after submersion, especially for children, where the dive reflex is the strongest. You can make your own dive reflex stronger by “exercising” it.
Real quick, a philosopher is anyone who expounds on a theory in a particular area of experience. All dopers are philosophers, because we all theorize on different topics.
I have to agree with 'threemae’I do believe " the being pulled out of a frozen lake" example is an example of the reflex. (I had to briefly interject)
There a theory called the “aquatic ape theory”. The idea is that humans evolved for a period of time while living primarily in water. It explains other things, like the nature of human body hair.
I don’t think it’s a very well accepted theory, but a web search should still come up with stuff.
Is this a response to immersion in water (as in diving) or simply to cold? Would the same thing happen when exposed to cold air? If so, how is it a “dive” reflex and not just a cold reflex? I’m not saying you’re wrong, just that this experiment doesn’t make it clear or provide enough evidence.
Yeah. You’re right. They can call it a dive reflex, but it ain’t. It’s a cold reflex.
The body protects its inner core temperature by closing down extremity circulation when the surface is exposed to sudden cold.
If you’re working outside in the cold, your hands will get cold and even frostbitten because of this, while you may remain toasty in your torso. Your body is attempting to conserve it’s heat by not pumping it willy-nilly to be lost to your extremeties.
While it does result in a lower use of oxygen, it doesn’t have anything to do with diving, except to make unprotected dives in cold water somewhat dangerous from a hypothermia standpoint.
Once you drown, and your heart stops beating, there is no blood being delivered to your brain or vital organs. You are dying if not dead. The cold greatly slows down the chemical processes of death, and revival even after a great period of time is still possible.
Refrigeration, and your body’s reaction to cold. That’s all that’s happening. Calling it a dive reflex is a huge misnomer.
Incidentally, if you practice holding your breath, you will almost always do better on subsequent attempts then your first one.
Finally, how long you can hold your breath is mainly a factor of preparation and tolerance for pain built up through conditioning. If your airway were to suddenly get clogged right now, you would struggle and remain conscious for somewhere near 4 minutes. If you hyperventilate and purge your body of carbon dioxide (don’t do this, it’s dangerous,) and then try to hold your breath, it’s possible to reach and excede that mark with relatively little discomfort.
Thanks for the explanation, Scylla. It sounds like the “dive” reflex in marine mammals would be more of a specialized extension of a basic cold reflex.
I have another question (hopefully not too much of a hijack). I’ve jumped into very cold rivers and lakes, either up in northern Saskatchewan or in the mountains at the base of glaciers (once my disgust at being filthy outweighs my dislike for bathing in frigid water) and experienced – after the first shock – a great rush of heat, so I feel toasty warm. This happens within seconds of jumping in. Is this related to the same reflex?
You got me on that one. I really have no idea. When I get in really cold water, I usually feel like I’m freezing my ass off.
I do know that the hot and cold sensations are related. Put somebody under duress, and show them a lit cigarette and tell them you are going to burn their back, then touch their back with an ice cube, they’ll feel like they’re being burned.
You just might be so cold, you’re thinking you’re warm.
On the other hand, it’s usually a dangerous situation when you start feeling hot when you’re freezing. People who freeze to death often strip off their clothes because they feel hot. It’s a serious sign of advanced hypothermia.
The converse of this; feeling cold on a very hot day while doing strenuous exercise or exposed to the sun is usually a sign of heat stroke.