We don't think it, we actually KNOW that humans evolved from monkeys. Well, creatures that used to be like monkeys. Monkeys that lived on Earth a very long time ago but are now extinct, so not the same monkeys you see at the zoo. Our closest living relatives today are actually apes, like the gorilla and chimpanzee. We did not evolve from gorillas or chimpanzees, but instead humans, gorillas and chimpanzees all evolved from the same monkey that lived a very very long time ago but no longer exists.

We know evolution occured because our genetic information- the code that tells our cells what to do and how to act in order for form the tissues and organs that make up our body- is almost EXACTLY the same as the genetic information that apes have (99.9% the same in fact)! Because our genetic information is very similar to apes, humans and apes share a lot of traits like:

- having hair, teeth, eyes and nails
- walking on two legs
- having an opposable thumb that you can move without moving your other fingers
- being able to do social things like learn from each other, feel emotions and care for one another

But it is important to note that the small differences in our genetic information make humans quite different from apes:

- we use our brains to really think and reason about the world around us
- we can speak because the structure of our voice box and throat allows us to form words
- we walk fully up right so we can use our hands to do other things
- we blush when we get embarrassed (humans are the only species known to do this!)
- we are not covered in hair

We don't. Human beings have an ancestor that was also the ancestor of monkeys. Think about it this way: you did not come from your cousin and nor did your cousin come from you. You both have an ancestor in common (specifically, your grandparents, if they're first cousins). Humans and monkeys are very distant cousins, humans and lemurs even more distant, and humans and pine trees even more distant yet, but we did not evolve from any of them any more than they evolved from us.

Why do we share an ancestor with monkeys? Because we have several things that we share in common that few or no other animals do. Apes (including humans) and monkeys both have thumbs. We have three-color vision (the ability to see green from yellow from red and tell them apart). We have several other details of the skeleton, and we share a lot more DNA in common than we do even with, for example, lemurs (primates that are neither apes nor monkeys). For this reason we think that our last ancestor that we share with monkeys lived a shorter time ago than with other kinds of animals.