I’ve often heard it said that in the next life cows become humans in the mode of goodness, tigers become humans in the mode of passion and monkeys become humans in the mode of ignorance. Here is something I have just found in Srila Prabhupada’s books that confirms at least some of this: “Those who come to the human form through the quality of sattva-guna were cows in their last animal incarnation. Those who come to the human form through the quality of rajo-guna were lions in their last animal incarnation. And those who come to the human form through the quality of tamo-guna were monkeys in their last animal incarnation.” (Srimad Bhagavatam 5.l4.30)