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It just seems like it would be a really cool thing to have gills and be able to populate the oceans in the same way we populate the land. We could have houses and shops and vehicles, andgo on walks/swims and just kind of live underwater.
Start a whole new second species of human here on earth maybe, Who knows?
I don't believe this. Sailfish, barracuda, tuna, huge mass, highly active... I'm sure they use a HELL of a lot more oxygen than I do on a good day. Gills extract MORE oxygen than lungs do, they're more efficient.
My unscientific opinion tho.
This article estimates at a 40kg sailfish uses about 2.7 megajoules per day of energy when hunting. That's about 650 kcal.
An 80kg human weighs about twice as much and needs about 3 times the energy, without even exertion.
Warm blooded animals spend a lot of energy just maintaining body temperature. Plus water doesn't have very much oxygen in it, compared to the atmosphere.
Oh sure, if you're going to use facts and science we may as well not even talk.
Seriously though, thanks for the insight.
This is the whole "if humans were going to have wings we'd have to redesign the whole organism from the ground up" fiasco all over again.
Exactly.
We still theoretically could, I guess, but people already have enough body image problems just from getting wrinkly or kinda bald, let alone being a freak mostly made of human-skin batwings.
Yeah, evolving lungs ended up clearing the way to make use of the much more plentiful oxygen in the air compared to what is dissolved in water. Amphibians and reptiles have pretty low metabolisms, but birds and mammals basically evolved endothermy (aka warm bloodedness), probably in support of much higher muscular power output. Ectotherms (aka cold blooded animals) have metabolisms that are correlated to temperature, which means they can't exert themselves as well when it's cold. Endothermy allowed animals to be warm all the time, and therefore use higher muscular power output in any environment, especially sustained.
That means mammals and birds were able to cover more distance, and survive in places where reptiles and amphibians can't, and all the advantages that carries.
That last line is one reason we're able to fish successfully. Even large fish tire out because they can't pull enough oxygen from the water to struggle forever.