TRANSMIGRATION

Originally the living entity is a spiritual being, but when he actually desires to enjoy this material world, he comes down.

From this verse we can understand that the living entity first accepts a body that is human in form, but gradually, due to his degraded activities, he falls into lower forms of life — into the animal, plant and aquatic forms.

By the gradual process of evolution, the living entity again attains the body of a human being and is given another chance to get out of the process of transmigration.

Sb 4.29.4 purport