What belief system saw all of creation as a continuum with man at the top of animal world?

Gregor, the protagonist of Kafka's The Metamorphosis, has various reasons to hate his job. He believes that the job is not suitable for him - it is too far away from his home, so he has to travel a lot; there are always new employees, so he has to meet new people every now and then (and he's not a sociable person); the meals are unsatisfactory; he doesn't feel any fulfillment from his job. The only reason why he keeps working there is because he owes his boss some money, so until he pays him off, he has to work for him.