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I have a concept for a species of arctic-dwelling organism (let’s just call it a polar bear) that evolved an organ that was able to produce microwaves, which it uses to tunnel through ice.

If such a thing is possible, my question is: which already-existing organ(s) would evolve into this new organ (like how electrocytes evolved from muscle cells in electric eels), what organic structures and processes would develop inside this organ, and what ramifications would this have on the organism’s physiology? As in, how would its body change in order to cope with this new organ?

Edit: thanks to your answers, I realize now that not only is evolving this organ incredibly improbable, but that microwaves are an incredibly inefficient method of melting ice, and that infrared rays would be better.
So, let’s call it an organic infrared generator, and the organ be housed inside an entirely unique genetically modified organism. What additional biological processes might it have to cope with the organ, and what would it look like?

TL;DR: generation of high power microwaves from organic mechanisms is very, very hard and evolutionarily unlikely. Microwaves are also a terrible way of tunnelling through ice. Note that polar bears and leopard seals don't bother in the real world; who are you to argue with those highly effective apex predators?

As another answer already touches on the inefficiency of melting ice (even more so when you consider that there's no energy-dense food in there to make the tunnelling worthwhile!) I won't go into that, but lets consider the physiological issues of microwave generation.

Microwave generators have two important kinds of material that are hard to come by in nature: microwave-transparent materials, to cover and protect the business end of the emitting device, and microwave-reflecting materials to ensure that all the microwaves go where they are wanted (eg. out the front) and aren't absorbed by the rest of the equipment which would cause undesirable power loss, heating and damage.

Lightweight polymers like polystyrene or polythene are easy to come by courtesy of modern chemistry and industry, but there aren't many good biological equivalents. The presence of any water is undesirable (because of the resulting energy loss, heat generation and ultimately physical damage that will result) and growing a water-free biological membrane sounds like an absolute nightmare, and something deeply unlikely to evolve naturally. It is remotely possible that you could have some sort of super-thin layer of specialised bone, horn, hair or tooth and have the extruding layer of cells die off, maybe.

Similarly, sheet metals and metal meshes have been available to humans for millenia, but bulk deposition of metals in organic creatures isn't a thing, let alone formation of nice smooth reflecting cavities. There's no obvious evolutionary path to such a trait... seems like mineral/protein composites that most tooth or bone or shell-bearing animals produce is quite good enough without the hassle and energetic expense of refining metals.

Finally, even if you've solved those two not-insignificant problems, you need to actually generate microwaves. Human approaches to this involve vacuum tubes (good luck evolving a vacuum-sealed cavity in a biological organism!) or semiconductors. The latter might just possibly be able to have some organic counterparts but: they are low power microwave sources, the sort useful for communication, perhaps, but not for generating the enormous amounts of power you need to melt enough ice to fit your body through.

While it's imaginable that an organ could evolve to emit low-powered microwaves, this is not a practical way of tunnelling through ice.

Melting ice - changing it from solid to liquid without substantially altering its temperature - takes a lot of energy. According to Wikipedia, enough energy to raise the temperature of an equal mass of water by 80°C. You then need to raise the temperature of the newly melted water enough to let it flow away before the heat leaks away into the surrounding ice and it freezes again.

Your creature needs to radiate all of that energy as microwaves without cooking itself, which is not plausible, supply rather more chemical energy to the microwave generator organ, which is not going to be 100% efficient, and eat enough to supply all that chemical energy as well as its normal needs. It's just not evolutionarily plausible. Evolving strong claws or teeth, and the muscles to use them to tunnel through ice is far more practical.

I agree with all the observations that such an organ would be as unlikely to evolve as Douglas Adam’s Babel Fish. But, if it did it would more than likely have these properties

1. A primary dimension — longest — an integer multiple of 6.25 cm. This would allow the cavity to resonate at the same frequency as a microwave oven ~2.3 GHz — the resonant frequency of hydrogen




2. The organ would be some sort MASER on the animal's skull or spine or shoulder blades or pelvis. The wavelength of the emission excites hydrogen atoms in molecules and while good for softening the ice, it's bad for organic tissue since it will tend to cause their proteins to cook. I think this means the rest of the bear, or walrus must be protected from the emission. I can’t think of a really good way to do that sort of metal shielding which would be odd. Conceptually a complex series of layered materials could form an interference pattern and act as an RF mirror but doesn’t seem evolutionarily likely




3. Some sort of chemical reaction similar to a primary cell battery to generate the power needed to drive the organic maser in the bear's skull (or wherever)

The maser wouldn’t melt the ice but since the skin depth of 2.3 GHZ is very long, the maser could soften the ice, causing fractures, that would allow the bear's great physical strength and adamantium claws — sorry, those are wolverines, right not bears — strong and sharp claws to carve the ice.