Asklemmy

There's not enough oxygen in water to support our metabolisms, even if we had gills.

Fish are adapted to conserve and use less oxygen, from slower metabolic rates to more options for anaerobic respiration that doesn't poison oneself from within.

Did Jeff Goldblum teach us nothing?

In short, we could, but the cost would be incredible.

All vertebrates are animals that develop from a series of segments, with a vertebra at the core. In our time from eel-like fish, we've specialised these segments so, for example, we have ribs on the vertebra corresponding to the rib cage.

To support arms and legs, specific vertebra have become highly specialised in the form of hips and shoulders.

Gills are composed of a series of gill arches, one on each vertebra in the neck area. These structures have (in eels) a lot of blood vessels to carry the blood that needs reoxygenation.

An interesting thing happened as the eel-like creatures differentiated, evolved jaws and ultimately ended up as mammals and humans: nature co-opted the specific vertebra that had these gill features and turned them into jaws and ears and a variety of other features in the head and neck. For example the tiny bones in your ear were once fish jawbones which were previously one (or more) gill arches.

The stupendously complex anatomy in this area comes from all the short-term 'decisions' evolution took to make all the magnificent creatures that inhabit the earth.

For example the nerve that connects the brain to the larynx (the recurrent laryngeal nerve) emerges from a vertebra high up in the neck, decends down under the aorta in the chest and then back up into the neck to the larynx. In the giraffe, the nerve is many meters long, even as it's direct path could be a few centimeters. The reason is that the heart used to be close to the gills in fish and sharks. As the heart moved in land animals, the nerve was caught in a loop around the critical aorta and it was 'pulled' along for the evolutionary ride.

So, in order to turn your gills back on, you need to unprogram 450m years of evolution of the structures you call your head, face and neck.

I'd recommend 'Your inner fish' by Shubin - it's a wonderful read and explains this in far more detail that I can manage.

Of all the Justice League members you could choose to have the powers of, you chose Aquaman?

cd ~/me
npm install gills —save

Yes, but being able to change genetic code does not mean being able to design entire organs and pop 'em in there during fetal development. That would be very challenging.

Gene editing has the most positive potential when it comes to things like curing/eradicating genetic diseases, doing microbiological research, or engineering metabolic products in microorgsnisms.

Pretty sure you can already get those you just need to have sex with enough siblings and cousins

maybe?, if we accept the mountains of dead human babies the research would inevitably produce.

Changing the color of your eye take so much changes that's impossible todo it, gills is going to need so much changes, and we don't even know what most of our genes do

Have you been watching a fairly terrible late1990/early2000s tv series starring jessica alba? I'm pretty sure they had some fish-mutants.

I don't think you can radically change a human's environment that much faster than nature, especially not a system so critical as breathing. The whole organism (including the internal microbiome) needs to co-evolve with itself and the ecosystem it is to survive in - to function effectively as an independent organism. I don't know how long it took cetaceans to evolve, but even they still breathe air at the surface - they're really just big flappy hippos.

I'm sure it's not impossible but I think you'd need, many, maybe thousands of generations for it to become something viable that can effectively provide enough oxygen to the other systems - or more likely adapt all the other systems to less oxygen. So it might have to live basically in a lab / sea-world for centuries. You might need scientists with unusual ethical standards to get to human - but an underwater rat? I'm sure you'd find a few Dr Mephestos out there eager to drown a few thousand of those.

Source: 100% ignorant opinion.

Yes, but not very good ones, probably. We're endotherms (hot blooded), and as a result we burn like 3 times as much oxygen as a similarly-sized shark. You'd need a lot of gills.

The rest of our body is also not very well suited to being underwater long-term. If you're adding gills you might as well change our silhouette, eyes, hair and skin as well, but you might not look very human afterwards. Maybe you could manage something merperson-ish, with an extra-flexible neck for looking towards where you swim and gills all along the tail? Sanitation would also be a bit of a nightmare, because if there's a sewage leak you get to breathe it.

The other option is just to get really good at diving conventionally, maybe enhance ourselves to make that easier, and build dry "indoor" spaces underwater. The technology to do it at a basic level isn't new, but there just hasn't been much interest in living that way yet.

Human embryos do have immature gills, but they are reused to create ears, jaw, tonsils, thymus, parathyroids and the large arteries in the neck and upper chest. We could add extra pairs and try to turn them into actual gills, although that would require removing the aortic arch and forcing all blood through the gills. Connecting them to the pulmonary system is not possible, as lungs and gills need different pressures (that's the whole reason we have two circuits). Maybe we could connect them in parallel to the aorta? That would only work as a backup, but with an adequate vasomotor system could do a nice job!

Its funny I did a paper on CRISPR in highschool and was very interested in the technology and one of the possible uses I mentioned was giving people gills to live underwater.

Sure. I take lungs now, give you gills next week.