Kino starts out in this novel as an all-around good dude. His life is built around diving for pearls, being manly, and spending quality time with his fam. He adores his wife, super adores his bouncing baby boy, and thinks about his ancestors:
Kino heard the creak of the rope when Juana took Coyotito out of his hanging box and cleaned him and hammocked him in her shawl in a loop that placed him close to her breast. Kino could see these things without looking at them. Juana sang softly an ancient song that had only three notes and yet endless variety of interval. And this was part of the family song too. It was all part. Sometimes it rose to an aching chord that caught the throat, saying this is safety, this is warmth, this is the Whole. (1.9)
Aww, shucks. What an adorable and heartwarming picture.
But then—or this wouldn't be much of a story—all hell breaks loose. No, we're not talking about the fact that his adorable baby gets stung by a scorpion (scorpions, man: why do they even exist?). We're talking about what should have been a stroke of luck—Kino hitting the pearl jackpot. This ends up throwing the town into a greedy, jealous frenzy... and really throws Kino off his good-guy streak. Yup: Kino ends up killing a total of four people. And that's after he's beaten his wife.
Sure—this isn't entirely his fault. He's being hounded by pretty much everyone else in the story, who all want to take away his pearl or at least some of his profits. But while he's the one being hounded, it's Kino himself that starts acting in a manner that's more than a little hound-like.
Although Kino never deviates from his masculine role he does stop being... entirely human. He starts acting in ways that are increasingly animalistic. Take a look:
Kino looked down at her and his teeth were bared. He hissed at her like a snake, and Juana stared at him with wide unfrightened eyes, like a sheep before the butcher. She knew there was murder in him, and it was all right; she had accepted it, and she would not resist or even protest. And then the rage left him and a sick disgust took its place. He turned away from her and walked up the beach and through the brush line. His senses were dulled by his emotion. (5.3)
And that is even before he's being chased through the wilderness and having to literally kill people in the attempt to protect his family. The teeth-baring and the snake-hissing only increase, and Kino's humanity only decreases. On the one hand, we can’t really expect much more of the guy; he’s out in the wilderness, his life is threatened, and his family is in danger. He has to get animalistic if he wants to survive.
But this is still deeply tragic, and not only because he fails to protect his son. Kino's beastly ways harken back to the Doctor (boo, hiss) saying that he wouldn't treat natives because he wasn't a veterinarian. In an incredibly brutal bit of irony, Kino is lending credence to the fact that the doctor compared natives to animals... by behaving like an animal. The colonialists that hear about Kino's exploits aren't going to think "Well, sure. But he was being hunted!" they're going to think "Oh yes. Natives are indeed all animals."
But Steinbeck isn't just going to give us that devastating bit of irony when it comes to Kino. He's going deeper. Check out this statement:
It is said that humans are never satisfied, that you give them one thing and they want something more. And this is said in disparagement, whereas it is one of the greatest talents the species has and one that has made it superior to animals that are satisfied with what they have. (3.13)
Okay: man is made superior to animals by his ability to seek a better life. Fair enough. Except... Kino becomes animalistic after he starts looking to climb the ladder of success. What are you playing at, Steinbeck?!
Here's our take: Kino is made more human, more civilized by his dreaming. Just like the pearl (check out the "Symbols" section), dreams aren’t bad per se—it’s society that screws them up. Society takes Kino and, for all his dreaming, beats him to the ground—into the status of an animal. He is left with no choice but to respond with the only weapons he has: instinct, physicality, and animalistic violence.