Last night my 14 yo was eating a sandwich and started choking. At no point was her airway completely obstructed, but it was pretty scary for a minute until she was able to cough out the piece of food.
But this reminds me of a question I have had for years. Why do humans have a single entrance to their windpipe? We have two lungs, but why only one opening to the trachea? Surely if there were two separate windpipes there would be a lot fewer deaths from choking. Isn’t this something that would normally be selected against evolutionarily? I could imagine choking being even more of an issue in the prehistoric days when meat was tougher and often uncooked.
But seriously, I was thinking of something on either side of the larynx. Yes, they could still be blocked simultaneously by a large enough piece of food, but it would be less likely than with only one.
Apparently not. There are no paired trachea system I’m aware of anywhere for any vertebrate. Birds have a very complicated respiratory system relative to mammals that allows for a routed unidirectional flow and more efficient oxygen exchange for flight. But birds will very occasionally choke to death on too large of a meal. Just doesn’t seem to happen often enough to overcome the engineering constraints.
You’re asking the wrong question. The issue isn’t “why don’t we have two windpipes?”; it should be, “Why does the trachea (‘windpipe’) connect to the same orifice and conduit (mouth and pharynx) as the esophagus? Both fish and cephalopods are smart enough to use entirely different pathways for nutrition and respiration, so why are we designed so poorly?
The answer, such as we can make the assertion, is one of evolutionary parsimony. As ‘fish’ started to evolve to more amphibious forms and gills were not suited for passively pulling oxygen from the much less dense air, gills developed structures that allowed for drawing and pressurizing air, but required musculature to drive the pumping action. This (probably) developed from structures already used to pull nutrients into the digestive system through the mouth, hence why lungs and the digestive system share a single conduit. (Although it is often incorrectly claimed that lungs evolved from the swim bladders that most modern fish have, in fact it is the other way around; swim bladders evolved from the very primitive lung structures that fished developed to live in oxygen-poor waters.)
There has never been a reason to evolve independent or redundant conduits. Nor is there an evolutionary pressure to select for having multiple conduits due to a hypothesized ‘choking hazard’. In fact, choking is primarily a human problem arising from the cooking and processing of food. In nature, carnivorous animals eating uncooked tissue do not masticate their food into small or soft enough bits to fit into the trachea; they eat whole chunks (generally as quickly as possible because they are likely protecting or ‘sharing’ the kill with others), and then frequently regurgitate and reconsume partially digested food, which is why your dog eats their own vomit. Most herbivores masticate their food extensively before swallowing. and omnivores like bears and apes eat a lot of small foods (berries, nuts, larvae, insects, and the occasional small animal or carrion, again uncooked). The choking hazards that we and our domestic pets experience is almost exclusively due to cooking food to a very compliant texture and cutting it into small bites that can potentially fit into and obstruct the esophagus.
I’ve read that vulnerability to choking is somewhat of a human specialty, which occurred as we gained the ability to talk and manipulate complicated sounds. It’s like our lower back issues that came along with bipedal locomotion freeing up the hands. Not that other animals can’t possibly choke on food, but they’re not nearly as likely to as we are.
Also, this would be a pretty big evolutionary change. Evolution works incrementally, and it’s hard to go from one to two in incremental steps. Maybe we’d go through a bi-lobal windpipe that was harder to completely plug, but it’d conceivably be quite a long process.
That by itself doesn’t mean there wouldn’t be an evolutionary pressure on humans. To the extent that there isn’t much evolutionary pressure, it may be because choking deaths aren’t that common. In the US, it’s only about 3000 people per year - and most of those deaths occur in people above child-rearing age.
If you to go the link, select “chart” instead of “data table”, then click on “choking” to highlight the age distribution I’m talking about.
So if there ain’t many choking deaths among people who have yet to produce independent adults, then there’s not much evolutionary pressure toward the development of a more choke-resistant respiratory system.
And then of course the other thing you need is chance mutations/variances that evolution can select for. If nobody in the past 50,000 years was born with more choke-resistant features than their peers (or they were born, but got et by a saber-toothed tiger before they could bear choke-resistant kids of their own), then evolution just never got a chance to make any headway.
Most of the more complex animals on Earth have bilateral symmetry for much of their systems. As a very crude rule of thumb, if a species has two of something they’re mirror images of each other.
I’d look at it the other way. Not that animals would evolve from where we are today toward a dual-windpipe system. But rather how did we evolve to the current two-into-one-back-into-two system?
We have two nostrils and two lungs. Why not two pipes to connect them ab initio? @Stranger_On_A_Train explained the actual reason, but we could readily imagine another path through evolution that led to dual systems from nostrils to lungs.
And most all, as @Stranger_On_A_Train also said, the OP’s question is sorta missing the point. Why does the plumbing for eating and breathing have any parts in common? If you wanted a robust design you wouldn’t do that. Further proof that “intelligent design” isn’t.
You give a lot of credit to creatures that fuck using the same holes they shit out of! I wouldn’t trade my equipment for an all purpose cloaca, I’ll tell you what!
The other pair of nostrils are just the connection between the nasal cavity and the pharynx, so serial to the other nostrils and part of the same two tubes.
Because having a second pathway to breathe through is advantageous, such as when the nose gets stuffed up or damaged. The mouth is the only other available opening in proximity. Also so filtering and moisturizing function of the nose can be bypassed during heavy exertion.
Because there’s an advantage to using the lungs to expel stuck food. The neck is a choke point in the body (literally and figuratively) so if food is going to get stuck, it’s better that it happens where the lungs can help, and as close to the mouth as possible.
I’m not saying our plumbing couldn’t be better, but I do wonder how many instances of choking to death are countered by choking and coughing it up. If the esophagus and trachea didn’t combine in the throat, I could see more instances of someone swallowing something too big for their esophagus and not having a way to eject it other than vomiting, which doesn’t seem to have as much force.
Think of it kind of like a toilet. They are (or should be) designed to clog, so that if it happens, it is at the toilet where you can get to it, not farther down the pipes where you can’t.
Lungs cannot expel food that gets stuck in the esophagus, and generally speaking the only objects that can get stuck there are broken bones and other objects with sharp barbs that stick into the canal and have to be dislodged by manual manipulation. The only food that can actually go into the windpipe and get stuck are very small pieces of relatively soft texture, or liquids that can block the laryngeal aditus. The muscles of the esophagus are quite powerful and their concerted peristaltic action is sufficient to push anything that you could potentially swallow back up into the mouth, as anyone who has observed a person in violent projectile vomiting might expect. It would take deliberately forcing some substantially oversized hard object or a material that absorbs gastric fluids and expands to get ‘stuck’ in the esophagus, and again, it would not be expelled by the lungs.
I’ve heard that whales and dolphins have completely separated respiratory and digestive tracts. So, if they get something stuck in their throats, it doesn’t cut off their air.
BTW, if you want to get biologist brownie points, refer to the limbs of the octopus as “arms,” not tentacles. Quoting Wikipedia: Tentacle" is a common umbrella term for cephalopod limbs. In teuthological context, octopuses have “arms” with suckers along their entire length while “tentacle” is reserved for appendages with suckers only near the end of the limb, which octopuses lack.
