“According to Vedic instructions, there are two paths for human activities. One is called pravritti-marga, and the other is called nivritti-marga. The basic principle for either of these paths is religious life. In animal life there is only pravritti-marga. Pravritti-marga means sense enjoyment, and nivritti-marga means spiritual advancement. In the life of animals and demons, there is no conception of nivritti-marga, nor is there any actual conception of pravritti-marga. Pravritti-marga maintains that even though one has the propensity for sense gratification, he can gratify his senses according to the directions of the Vedic injunctions.” (Shrila Prabhupada, Shrimad Bhagavatam, 4.25.39 Purport)