People used to tell stories to children. These stories are passed on and extended. Children brains can be formed, so children will believe those stories to be true and pass them on. The stories have become religion. That is why people believe in stories from bible, koran etc and therefore think that there is a god. We could also believe to live on a toe nail of a really big giant (guess what the score on a debate with that statement would be...). There is no god unless we have strong indications or proof which we don't so there is no reason to think that this statement is true. Stories from the past are no proof or even indications as they are mostly made up.

If you believe in god, you are brainwashed pretty well by parents and/or society. (to be verified by the fact that your belief matches the belief of people around you...)

If you look at how the whole universe developed, it is clear that all living things are just a chemical reaction that really got out of control. Because the chance was there, chemical and physical processes developed into what we call life. So basically we are all the same. Why should there be a different "value" based on size, brains etc and who could define this difference as there is no objective observer (assuming that there is no creature with a beard watching us from above)? Yes an ant is equal to me.

And for people who say no: what if 50 years ago, someone posted a similar question here about black people being equal to white people? Nowadays most will say: "sure, they are equal", but not 50 years ago. So maybe in 50 more years, people will realize that animals are equal to humans.