It appears that during the time of the Pāṇḍavas, free contact between man and woman was allowed in certain conditions only. The higher caste men, namely the brāhmaṇas and kṣatriyas, could accept a woman of the vaiśya or the śūdra community, but a man from the lower castes could not contact a woman of the higher caste. Even a kṣatriya could not contact a woman of the brāhmaṇa caste. Such contact between man and woman was known as uttama and adhama. Contact of a brāhmaṇa with a kṣatriya woman is uttama, but the contact of a kṣatriya with a brāhmaṇa woman is adhama and therefore condemned. A woman approaching a man for contact should never be refused, but at the same time the discretion as above mentioned may also be considered. Bhīma was approached by Hiḍimbī from a community lower than the śūdras, and Yayāti refused to marry the daughter of Śukrācārya because of Śukrācārya’s being a brāhmaṇa. Vyāsadeva, a brāhmaṇa, was called to beget Pāṇḍu and Dhṛtarāṣṭra. Satyavatī belonged to a family of fishermen, but Parāśara, a great brāhmaṇa, begot in her Vyāsadeva. So there are so many examples of contacts with woman, but in all cases the contacts were not abominable nor were the results of such contacts bad. Contact between man and woman is natural, but that also must be carried out under regulative principles so that social consecration may not be disturbed or unwanted worthless population be increased for the unrest of the world.
Ref >> Srila Prabhupada Vani.