ORIGIN OF PURU VANSH / YAYATI / NAHUSH
Daksha's daughter Aditi got married to Sage Kasyap, and they were blessed with a son named Vivasvaan.
Vivasvaan too was blessed with a son Yam, who was known as Vaivasvat and another son named Manu.
Manu was a dharmatma and was the pride of Suryavansha. Even Manuvansh originated from him. Manu's child ILA gave birth to Pururava who was the ruler of all 13 dweepas.
King Pururava and Urvashi were blessed with 6 sons i.e Ayu, Dheeman, Amavasu, Drudayu, Vanayu and Shatayu.
Ayu and Swarbhanu Kumari were blessed with 5 sons i.e Nahush, Vrudhsharma, Raji, Gaya, and Anen.
Nahush was brave and strong. He was even appointed to the throne of Indra but due to his bad deeds, he was cursed by Sage Agastya.
Nahush was blessed with 6 sons, One of them was Yayati who ruled the earth and did many Yagyas.
Yayati and Devyani were blessed with 2 sons i.e Yadu and Turvasu. Yayati and Sharmeshtha were blessed with 2 sons i.e Anu and Puru. Yayati ruled his kingdom nicely but one day he was cursed by Sage to attain old age(वृद्धावस्था).
Yayati then requested all his 4 sons to take his old age (वृद्धावस्था) and to give their youth(युवनावस्था) as he wanted to enjoy worldly comforts, He also told one who accepts this will need to run his kingdom. Then Yayati's son Puru accepted his fathers request. After Puru was ruling Yayati's kingdom and with Yayati enjoying the worldly comforts, but after sometime Yayati realized that this was not right and then he gave the youth (युवनावस्था) back to Puru and went along with his wife to Brihgutangu mountain for Tapasya. And after few days he attained Swarga lok. Yayati was very much happy with Puru and blessed him that his Vansh will be known as Paurav Vansh(पौरव वंश) .