The main difference between animal emotions and human emotions is that animals don't have mixed emotions the way normal people do. Animals aren't ambivalent; they don't have love-hate relationships with each other or with people. That's one of the reasons humans love animals so much; animals are loyal. If an animal loves you he loves you no matter what. He doesn't care what you look like or how much money you make.
This is another connection between autism and animals: autistic people have mostly simple emotions, too. That's why normal people describe us as innocent. An autistic person's feelings are direct and open, just like animal feelings. We don't hide our feelings, and we aren't ambivalent. I can't even imagine what it would be like to have feelings of love and hate for the same person.
Some people will probably think this is an insulting thing to say about autistic people, but one thing I appreciate about being autistic is that I don't have to deal with all the emotional craziness my students do. I had one fantastic student who flunked out of school because she broke up with her boyfriend. There's so much psychodrama in normal people's lives. Animals never have psychodrama.
Children don't, either. Emotionally, children are more like animals and autistic people, because children's frontal lobes are still growing and don't mature until sometime in early adulthood. I mentioned earlier that the frontal lobes are one big association cortex, tying everything together, including emotions like love and hate that would probably be better off staying separate. That's another reason why a dog can be like a person's child: children's emotions are straightforward and loyal like a dog's. A seven-year-old boy or girl will race through the house to greet Dad when he comes from work the same way a dog will. I think animals, children, and autistic people have simpler emotions because their brains have less ability to make connections, so their emotions stay more separate and compartmentalized.
Of course, no one knows why an autistic grown-up has trouble making connections, since our frontal lobes are normal-sized. All we know right now is that researchers find "decreased connectivity among cortical regions and between the cortex and subcortex." The way I visualize it is that a normal brain is like a big corporate office building with telephones, faxes, e-mail, messengers, people walking around and talking -- a big corporation has zillions of ways for messages to get from one place to another. The autistic brain is like the same big corporate office building where the only way for anyone to talk to anyone else is by fax. There's no telephone, no e-mail, no messengers, and no people walking around talking to each other. Just faxes. So a lot less stuff is getting through as a consequence, and everything starts to break down. Some messages get through okay; other messages get distorted when the fax misprints or the paper jams; other messages don't get through at all.
The point is that even though autistic people have a normal-sized neocortex including normal-sized frontal lobes, our brains function as if our frontal lobes were either much smaller or not fully developed. Our brains function more like a child's brain or an animal's brain, but for different reasons.
When the different parts of the brain are relatively separate from each other and don't communicate well, you end up with simple, clear emotions due to compartmentalization. A child can be furious at his mom or dad one second, then completely forget about it the next, because being mad and being happy are separate states. A child hops from one to the other depending on the situation.
You see the exact same thing with animals. Strong emotions in animals are usually like a sudden thunderstorm, They blow in and then blow back out. Two dogs who live together in the same house can be snarling one second, then go back to being best friends the next. Normal people need a lot more time to get over an angry emotion, and even when a normal adult does get over a bad emotion he's made a lasting connection between the angry emotion and the person or situation that made him angry. When a normal person gets furiously angry with a person he loves, his brain hooks up anger and love and remembers it. Thanks to his highly developed frontal lobes, which connect everything up with everything else, his brain learns to have mixed emotions about that person or situation.