Humans are different for the same reasons that members of any species are different. Except for identical twins, no two people are the same genetically. Even identical twins look slightly different, because their genes have interacted with the environment in slightly different ways.

Yes, people are one kind of animal. Mammals are one kind of animal (furry ones with backbones). Primates are one kind of mammal. And humans (Homo sapiens is our official name) are one kind of primate.

It's important to remember that species exhibit lots of variation--no two individuals are exactly alike. Humans are just like other living things in this regard.

Great question!

There are many ways you can say that humans are different. One way is in our minds. Everyone has their own mind, which collects experiences as they grow up. Some of these experiences will be shared with other people, and some of them will be unique to that person. For example, twins will grow up with many similar experiences, but not all of them will be exactly the same.

Animal minds are just as different from each other. The mind of one cat is different from the mind of another cat, and that will be true no matter what their age, gender, color, or race is.

We are all the same species, because any man and woman can have children, and their children can have children. On the other hand, cats and dogs cannot have children together, because they are different species. (There are some more complicated cases. For example, horses and donkeys can have children called mules, even though they are different species. But mules cannot have children.)

There are many races of humans, but this is not really an important difference. Race is just a way to say how we look, but it doesn't say anything about how we think.