Why does nitrogen cause you to just pass out but carbon dioxide causes you to suffocated and feel it? Is it because of the oxygen in carbon dioxide?
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Others have covered the “why does my body experience pain when asphyxiation from CO2”, but it is interesting to consider why we (and all animals) have this reaction to CO2 specifically, but not to other gases.
A long time ago, in the earliest era of animals that took oxygen in and exhaled CO2, there was a danger of staying in one place with poor circulation, and dying of too little oxygen and too much CO2. Pain is a good motivator, and the creatures that experienced pain when staying somewhere unsafe from a gaseous content perspective survived, and those that did not died in caves and underwater bubbles.
In those days, fire was all but unheard of, and there was no normal way to get too much nitrogen. In other words, good levels of oxygen would also mean good (ie., sufficiently low) levels of CO2 would be normal, and poor levels (ie., sufficiently high) of CO2 would also mean poor levels of oxygen. So, all we had to have was one detection method. As others have indicated, it was easier to use the acidic nature of CO2 to detect high levels of CO2, instead of having to evolve a much more complex method of detecting low levels of oxygen.
Since the two levels were inversely proportional, just our internal CO2 detectors alone did the job wonderfully.
Even when our human-like ancestors discovered fire and started to use it in more closed areas, CO2 was always a much greater danger than carbon monoxide or a lack of oxygen, so our one little internal CO2 sensor still did its job like a champ.
It has only been in the last few hundred or few thousand years, a mere blink of the eye in evolutionary terms, that humans have introduced gaseous dangers that our internal CO2 detectors might not warn us about. Carbon monoxide just makes us sleepy. A lack of oxygen gives us headaches but does not trigger a biological response like CO2. Too much nitrogen or helium that reduces the amount of oxygen likewise does not trigger a pain response that demands action, and can allow asphyxiation without the person ever knowing what is wrong.
All because our bodies are only good at detecting the one gas, CO2, that has always been a danger.
(So, what is our solution? Like with so many other things, where biology and evolution cannot help our bodies cope with modern life, we use our brains. We used canaries, and would see if they passed out, since they would pass out before the humans would. We used flames and other visual clues. Now, we have detectors that watch for CO2, CO, low O2 levels, and anything else we might need to keep an eye on.)
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