"That's sci-fi. I'm talking about real life"
-Am talking about toxic fandoms, which exist in real life.
"Homo Neanderthalensis was capable of interbreeding with Homo Sapiens. If they produced fertile offspring, that means they weren't a completely different species."
-Lions are able to intebreed with tigers, leopards and jaguars and are still different species. And that is not how hybridization works. According to Haldane's rule the first generations hybrids will have sterile males but fertile females, fertile males appear after generations of backcrossing.
"Neanderthals were pretty similar to humans"
-Not exactly. They where similar in being humanoid but furthermore there are several differences:
1.Unlike humans, Neanderthals where not neotenus, which is why they can grow a great ape bone eyebrow. Humans are the only neotenic great apes.
2.They have a robust, barrel shaped and chubby body.
3.They have large round noses.
4.They had short limb proportions.
5.They where very masculine, to the point females got masculated.
They where also different in behaviour. Unlike other anthropoid species, who chase their prey for miles to later deliver the killing blow, Neanderthals engaged in physical combat with their prey. They where also found to be extremely aggresive, making them possibly the most aggresive species of the Homo genus.
Several anthropoid species also exibited unique behaviours:
-Homo naledi where arboreal and loved trees.
-Homo anteccesor where cannibals.
-Homo floresiensis where small weaklings who got eaten by komodo dragons.
-Homo erectus where agile hunters, similar to the Yautja.