Why have no mammals evolved to breath underwater despite lots of them living there?
Is there anything inherently incompatible with the way mammal bodies work that doesn't allow for this? Or is it simply due to the required genetic coincidences not having happened?
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Mammals have developed other adaptations that have allowed them to thrive in oceans without the need to breathe water. Mainly they can hold their breath for a long enough time to obtain food, but there are many many more advantages. If a creature can get to the point where it can reproduce, that's all you need for the species to continue.
Now in some hypothetical future maybe the skin of marine mammals is able to absorb some amount of oxygen so that it extends how long they can stay under water. This may confer an advantage that allows more offspring.
These offspring may have mutations on these absorbent skin cells that even further differentiate and become some gill. Convergent evolution happens all the time. See squid eyes and mammal eyes.
Hope that gives you a better reference for thinking about this.
It's primarily because the required genetic coincidences have not happened. Extracting oxygen from water an inserting into the bloodstream is a complicated process and is the sort of thing a microorganism evolves, not a mammal. Especially when there is an intermediate solution that satisfices, like surfacing to breath air.
But there's more to say on this. Even if dolphins had gills, they would still need to breath air. Mammals have much faster metabolisms that consume a lot more oxygen than the metabolisms of fish. The volume of water that would need to pass through gills or gill-like structures would be infeasible.
Faster metabolism means more energy, faster growth, smarter, etc so long as you can supply it with food, so the nature of mammalian life is fundamentally different than that of fish. Fish could not support the huge body sizes of creatures like the whale without first evolving air-breathing lungs.
Pretty good answers actually. Thanks.
>Fish could not support the huge body sizes of creatures like the whale without first evolving air-breathing lungs.
Lungs are serious energy draining business and you expect mammals to mutate lungs away? There are freaking lobe finned fish in the Pacific ocean with the beginning of lungs dating back to over 300 million years ago.
The blue whale is 7 times the size of the whale shark.
It is still a fucking fish and it shows your statement is false
Growing big is not that difficult.
>growing big is not that difficult
YOU'RE RIGHT GOD DAMN IT
WHATEVER IT TAKES
BIGGER THAN A BLUE WHALE
LEAVE HUMANITY BEHIND
Most of evolution is "tinker"ing. An alteration of an older structure rather than the addition of a newer structure. This is why we don't see birds evolve wings with four legs. In simple terms, it's easier for the nose to develop into a blowhole then for a gill system to develop.
How come none of them have developed snorkels?
The blue whale is pretty much end of the line when it comes to size, any bigger and the blood vessels will collapse under the pressure.
>pressure
>collapse
external pressure (ie from the water) is equilibrated internally. in other words, they simply pack more water molecules into their cells naturally so there is no pressure gradient across the membrane. thats why they die when you bring them to the surface, because all that extra water comes out if there is not external pressure holding it in, and they explode.
that leaves internal pressure, which is positive by default (the heart pushes on the blood), so the vessels wouldnt collapse, they would explode.
either way, that is not a limit for their size.
blue-fin tuna swim faster than dolphins and are of similar size when full grown. there are numerous other examples of you being wrong.
∞ SCOOPS
Gills don't immediately stop working if you expose them to air for short periods of time such that they dont dry out. In fact, they work even better just as long as they can maintain a thin film of moisture due to quick exchange with the atmosphere which is enriched with oxygen compared to the water (this is how your lungs work, and how they evolved).
Taking a gulp of water into your lungs, on the other hand, results in you shutting down the activity of the tissue because it takes very little water to kill the diffusion rate across the boundary.
So one of those processes doesn't stop the organ from working, and the organism has to adapt to momentary increased oxygen levels. The other process stops the organ from functioning for the most part, and the organism has to adapt to drastically decreased oxygen levels.
One of those allows for a much greater probability of success, we are talking many orders of magnitude.
also, the air has way more oxygen than water
That's what a blow hole is .
Lungs evolved from Gills, so they could evolve back again. You don't answer OP's question, which is why they don't do that.
In other words, there is a reason that it is easier for a mammal to evolve a blowhole from its nose instead of evolving gills back from its lungs, and it is not the reason you gave.
Alright well if you're looking at it that way then I think someone else already answered.
You can make gradual changes from gills to lungs but not lungs to gills.