I just watched a Nature show on mustangs. A crippled foal was born, and when it couldn't keep up with the band they started to abandon it. Another herd moved in, and many showed solicitous interest in the baby, until the stallion got there. He took one sniff and then violently killed the baby. Both his own herd and the original herd tried to fight him off but it was no use. It was hard to watch. It's the same thing lions do if a male comes upon cubs that are not his own.
This has a lot to do with jealousy. It's a way of ensuring more resources for his own babies by getting rid of someone elses.

Not that we need to act in horrible ways like animals sometimes do, because we hopefully have more control of ourselves and understand right and wrong, but I think our feelings are rooted in the fact that we are animals.

I have a question about non jealousy, in a situation when jealousy might be appropriate or expected. Where does that come from? I'm thinking of times when various things have happened when another person might have been extremely jealous, and I'm just not. At all. If anything, I was amused. So, what does that mean?