Without quoting your entire post this time, I'd just like to respond to a few points.
"Well, when you say Ice Age, remember that much, if not most, of humanity was not braving the cold that was more so in the Northern Hemisphere. And so even now when you go to rural and indigenous populations today, it's by far a plant-based diet."
I live in North America and descend from the North American indigenous people. They eat a lot of meat, and they're really good at cooking it. As far back as you can look into their history, they eat meat.
"Evolution is pretty consistent. Even across species after deviation. It's also slow for higher-order species - we have few young and they mature slowly, and the genome is highly resistant to change/error. We may have different mass, height, complexion, etc., but we evolved with a particular diet to which we are best adapted, even while being flexible."
Sorry, bro, but mostly false. As I've already said, I require a meat-based diet to reach my fullest potential. For some reason, however, I seem to attract women who eat mostly plants. One of the women I've been with described to me how she had trouble digesting meats and couldn't eat too much. I am the opposite. I have no trouble eating or digesting meat. It makes me feel whole instead of making me feel troubled. That's a pretty big deviation. It was from this relationship I learned that people could have drastically different body types and require different nutrients. Her bloodline descended from Hawaii--probably why she wasn't a big meat eater. I imagine there were not many buffalo roaming the Hawaiian islands. Probably the most common and available meat would have been fish, with not much else to choose from. Since her bloodline was eating plants and fish while mine was eating buffalo, it makes perfect sense that our bloodlines evolved differently.
Our genome is designed for change, not only based on what works, but also based on error. There is a tribe in Africa which has an extra joint in their knee (or perhaps it was their foot), and they are able to jump 6 feet into the air. People who live in Europe are often able to bend their legs and feet into yoga poses that Americans are unable to perform, because American children don't usually bend their feet in that way. Black people have a completely different muscular structure than white people. Across the human race, there are innumerable branches of human evolution, all occurring in different ways. Just like how there are venomous snakes and non-venomous garden snakes.
"Muscle growth is mostly just sweling"
You should totally start working out, bro. If you think muscle growth is just swelling, wait until you actually start getting gains. Working out improves your mood, coordination, and gives you an outlet for pent up anger and unreleased sexual energy. People who work out often are more connected and aware of the things happening around them, as well as in greater control of their mood than people who don't. Except for steroid users who are typically on-edge. Good thing I don't use steroids!
Before I started working out, I was a bit of a klutz, constantly dropping things on the floor, etc. Now if I ever drop something, I seem to always catch it before it even travels a foot from my hand! This comes from working out, my friend.
The animals you mentioned at the end of your post, btw, have tremendous muscles because of the constant physical demands they put on themselves while living in the wild. I mean, gorillas? If you were swinging from tree to tree and lifting your entire body weight all day, you'd be ripped too! That's why I do pull-ups. Rhinos have to use the whole force of their body to impale somebody with their horn. They aren't just born with big muscles, bro. They have physiologies that have not evolved to require meat, because their ancestors never really ate it. My ancestors ate predominantly meat for generations. In any case, my case or theirs, it is the physical demand which caused our muscles to grow. A muscular person has a baby and that baby is more likely to develop muscles more easily. That's evolution. A man eats meat all his life, and it teaches his body to break down and use the proteins in the meat incredibly efficiently. This is also evolution
One place I agree with you is that if you don't eat plants and fruits, you will be a very dehydrated, hungry, angry man. Whatever anyone's body type is, they should always make sure to eat whatever it is their body needs, and to exclude whatever causes them harm. For me, I had to learn to eat more meat, drink more water, and do less drugs. And I thank God for all the progress I've made! There are plenty of meat-eaters who have the body type that requires meat. If you find one that doesn't eat enough fruit or veggies, you'll be putting your advice in just the right place.
And now, without further ado, I'd like to share my favorite character from Dragon Ball:
Dude is so ridiculously huge and cut lol. Must be all that buffalo meat!
Btw, if you notice, their spears are mostly for hunting. This is also true in real-life. In combat, the Natives would use tomahaks, bows, guns, clubs, and hatchets. The spear was still used in combat but not as often as these other weapons. Bows and of course guns were not invented by the native americans. Much like horses, they obtained these tools from another culture and mastered them.