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There are already answered, so I'll just write cool stuff.

Just like life, it's not black and white or acid and basic. It's just a big mass of chemical equilibrium. Even in a cell, you have different pH for organelles and stuff.

Fun fact : in mitochondria, we use glucose (super complex stuff) to send protons (H+ ions to be simple) in the outer area of the mitochondria. Because the amont of protons is very high in this area (acidic) and lower in the center area (less acidic) while being separated by a membrane, the protons want to go back and they can go through massive barrage that use their force to generate energy. It's called the proton motrice force and it's basically a protein water barrage that generate energy for your cell. Because we spend less energy moving the protons up than they generate by going back, excess energy woohoo. That's breathing baby

Tldr : We didn't invent the principle of water barrages, cells (bacteria) did.

Look up videos of ATP synthase on YouTube, and in the litterature if you want more infos. Super dope stuff.

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Plus once humans left the really warm area we seem go have had figured clothing out. Covering yourself in the fur of the animals you hunt is more efficient then growing that fur yourself.

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This theory relates to persistence hunting in particular. Losing fur would not be useful for any other type of hunting.

Thank you this is fascinating! Do they still present as either male or female in some way, even though they can’t produce sperm or eggs? Or are all mules physically non-binary in some way?

Thanks! This is what I knew happened but didn’t remember enough to explain it. I just know my veins and arteries still work pretty normally.

Wow, thanks!

This so much. I was wondering the other day about how humans conquered the coldest climates for millions of years, but never regained any fur to brace themselves against the cold. Until I went for a hike in the snow and quickly had to remove my jacket at - 10C because damn, bodies produce a lot of heat when moving.

Are there any other hunting mammals that have lost their fur?

The term "hybrid" exists for this very reason. It's to specify the product of two species, which is imbued by nature with DNA compatibility issues that either partially or entirely prohibit the free diffusion of genes into a receiving population. In short, that example of offspring (mules, in this case) is not "viable" by definition. In this case, because mules are infertile, there's not a reproductive vector for a horse population to have donkey dna in it, or vice versa... with extremely rare exceptions. In other words, "close enough to an absolute that we consider them distinct."

Ligers, Zonkeys, Jaglions, pumapards, coydogs, wholphins... there's plenty of examples of hybrids in nature. Chimpanzees have 48 chromosomes, humans have 46, so yes there is a similar problem, not to mention a world of ethical constraints on ever testing that in a labratory setting.

Interestingly, human chromosome #2 appears to be the product of chromosome fusion in our genetic history, which apears to be the explanation for how we "lost" a pair of chromosomes with respect to our closest cousins.

It depends on what species of bat you're referring to but as a blanket statement, it seems bats have the ability to limit certain responses to diseases like inflammation. It's not that bats are immune to viruses or anything, they simply have a much higher tolerance for diseases. A lot of the damage caused by illnesses is our body's reaction and how it fights it off. Things like fever which is designed to kill off infections also significantly disrupts the body and in some cases can cause as much if not more damage than the actual infection or virus.

Bats have the ability to control their body's response to diseases much more than other animals. This may also explain their relatively long lifespans. So they can act normally despite carrying a viral load that would make other animals like humans go nuts trying to get rid of it.

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are there any other examples of this in nature?

do ligers have the same issue in terms of reproducing?

is this why a chimpanzee and a human couldn't reproduce?

Good answer, a quick correction: even if the math is correct, it doesn't necessarily mean that everything the math predicts has to be real. That's indeed what happened with Dirac, but it doesn't have to be true for all mathematical models of the physical world.

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Can you give some examples of the kinds of explanations that are still accepted in the field? Like, "Here's a trait that [some animal] has. Here's the uncontroversial scientific consensus on how it evolved."?

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Blood vessels have branches. If you seal off one branch the blood still flows to the tissues through other branches. It’s like turning off the kitchen tap in your house — water can still flow to the bathroom sink or shower.