Srimad Bhagavatam Canto 04, Chapter 25, Text 38

SB 4.25.38

kam nu tvad-anyam ramaye
 hy arati-jñam akovidam
 asvastana-vidam pasum
How can I expect to unite with others, who are neither conversant about sex nor capable of knowing how to enjoy life while living or after death? Such foolish persons are like animals because they do not know the process of sense enjoyment in this life and after death.
Since there are 8,400,000 species of life, there are also many different living conditions. In the lower grades of life (in plant and tree life) there is no system for sexual intercourse. In the upper grades (in the life of birds and bees) there is sex, but the insects and animals do not know how to actually enjoy sex life. In the human form of life, however, there is full knowledge of how to enjoy sex. Indeed, there are many so-called philosophers who give directions on how to enjoy sex life. There is even a science called kama-sastra, which is the science of sex. In human life there are also such divisions as brahmacarya, grhastha, vanaprastha and sannyasa. There is no sex life except in the grhastha, or householder, asrama. The brahmacari is not allowed any sex, a vanaprastha voluntarily refrains from sex, and the sannyasi is completely renounced. The karmis do not practice brahmacarya, vanaprastha or sannyasa life, for they are very much interested in grhastha life. In other words, a human being is very much materially inclined. Indeed, all living entities are materially inclined. They prefer grhastha life because there is a concession for sex. The karmis think the other statuses of life are worse than animal life, for animals also have sex whereas the brahmacari, vanaprastha and sannyasi completely give up sex. The karmis, therefore, abhor these orders of spiritual life.
Srimad Bhagavatam Canto 04, Chapter 25, Text 37
Srimad Bhagavatam Canto 04, Chapter 25, Text 39