I say luckily for us he did not reach us, and I might also add luckily for himself, for there [was] only a small beaker of water and some soddened ship's biscuits with us […]. (1.3)
Put any person in an extreme situation, and our primitive side will show. Prendick tries to be reasonable about being lucky that a man died, and maybe he's right. Still, you've got to admit, that's pretty cold. Primitive and coldblooded.
The black hesitated before them, and this gave the red-haired man time to come up with him and deliver a tremendous blow between the shoulder-blades. (3.14)
M'ling is a Beast Folk and supposedly more primitive than a tried-and-true human. So, it's interesting that the primal act in this scene is performed by the oh-so pleasant Captain Davis.
I refused to go aboard her, and flung myself full-length on the deck. In the end they swung me into her by a rope—for they had no stern ladder—and cut me adrift. (5.25)
In theory, civilization has rules, and by following them, we'll stay civilized instead of primitive. However, Davis's men are only following the rules, but we'd qualify trying to throw a man into the middle of the Pacific a pretty weak thing to do. Guess it's less about just following rules and more about which rules to follow.
Without taking my eyes off the black form before me I stooped and picked up this lump of rock. (9.38)
It's not a coincidence that Prendick defends himself with a rock, weapon of choice for prehistoric man. Sure beats the alternative though.
"Back to the House of Pain—back to the House of Pain," gabbled the Ape Man, as though the idea was sweet to him. (16.70)
In terms of being primitive, the Beast Folk aren't primitive because their society is less tech savvy than ours. According to the novel, they're primitive because they enjoy the idea of another creature's pain. Of course, a civilized human would never do something like… that… oh... never mind.
Poor brutes! I began to see the viler aspect of Moreau's cruelty. I had not thought before of the pain and trouble that came to these poor victims after they had passed from Moreau's hands. (16.90)
Prendick realizes that what's really gotta stink for the "brutes" is not just the pain they endure on Moreau's operating table. It's also the messed-up-ness that's comes with the whole half-man half-beast thing. Moreau takes it to a whole 'nother level of savagery.
"You've made a beast of yourself,—to the beasts you may go." (19.16)
We're not saying that alcohol makes people act primitively—though it certainly doesn't seem to do the opposite either. However, here, Prendick tells Montgomery that the booze has brought to the surface his primitive nature.
A sudden convulsion of rage shook me. I was almost moved to batter his foolish head in, as he lay there helpless at my feet. Then suddenly his hand moved, so feebly, so pitifully, that my wrath vanished. (19.38)
Initially, Prendick feels a savage rage toward Montgomery and for good reason. The man broke his boat. But in this case, sympathy acts as the antidote to primitivity's poison.
The change was slow and inevitable. For them and for me it came without any definite shock. (21.40)
The Law is no more, and Prendick's ability to punish those who break it has vanished. On any other tropical island, that would mean party time. Here it means bye-bye civilization and hello chaos.
I could not persuade myself that the men and women I met were not also another Beast People, animals half-wrought into the outward image of human souls, and that they would presently being to revert,—to show first this bestial mark and then that." (22.5)
Prendick sees the mark of primitivity in the so-called civilized citizens of London. They cannot escape the fact that, just like the Beast Folk, they are still animals. And that's London! To really see humanity acting out its animality, you need to be in LA when the Lakers take home the trophy.