@AlexP Also horse racing, because of the same reason as motor sports.

@L.Dutch So is a mule not alive? Even if you have a male and female mule, they can't reproduce.

Then there are parasites. If you don't eat animals you reduce the parasites you are exposed to, but parasites can also come in things like water and boiling the water would be killing them, and they are not all necessarily unicellular.

But if you're doing something like selective breeding, how are you disposing of the rejects? Surely you're not caring for them until they have a natural death, nor are you going to transplant each and every one into a favourable environment. Also, I don't think it's easy to domesticate plants as easily as you imply. Have you read Germs, Guns, and Steel? Humans have apparently gone through exhaustive efforts to end up with farm animals and plants that we have and on the whole, it's not a lot. Place this criteria on top of that and it dwindles.

@user6760 Specifically, warthogs.

@fgysin Humans walks just fine and we have baggage carts or our bags have wheels, yet we have horizontal moving belts at airports. Elevators would not go away.

@Nosajimiki Well, your hand is a bad example of that because it also does not contain enough room either which is why all your finger muscles are in your forearm.

@MatijaNalis The stages of mechanical transmission part and weight of structural materials makes sense. The weight of the motor though, not so much. Someone recently on here was arguing saying that motors and cars have better power to weight than muscle. I was working off a Stephen Vogel reference saying that the power-weight of motor and muscle were about the same. But then they brought up how a 700HP car weighs much less than 700 horses, even after you account for extraneous mass of the horse.

How does this work out? Because motors can be 90%+ efficient. So where is the 7x reduction in power consumption coming from?

@Questor A human maintains homeostasis though. A robot, not necessarily unless you really want to simulate the body warmth thing. Waste of energy for the most part.

@JustinHilyard I will look up how mosquitoes do it , but they are a completely different lineage. Might not have anything and just uses blood pressure. EDIT: Mosquitoes have muscular pistons pumps in their heads. Makes sense since I guess they need to drink water and nectar and other stuff too. Not just blood from a live creature.

@JustinHilyard Nature need not followed human sandboxes.

@RobertRapplean Without looking anything up, I'm thinking a crop is just for storage, a gizzard adds on a mechanical digestion function, and a stomach adds on a chemical digestion function.

Leeches have a crop but no stomach. Crop just being an enlarged gut to store. Not sure if the spider stomach is vestigial or if it has other functions a crop does not.

Define exactly what you mean by stomach. Because sometimes they have a crop instead of a stomach, sometimes they have both. A crop is just an enlarged part to store.

@RobbieGoodwin The good old propellant problem. So difficult to explain away even in fiction that The Expanse basically had to ignore it in otherwise the highly dynamic spacecraft activities required for the story be implausible.