The affixes añ and yat come after the word manu and the augment ṣuk is added when these affixes follow provided that the whole word so formed denotes a jāti (class name).,
Karika
अपत्ये कुत्सिते मूढे मनोरौत्सर्गिकः स्मृतः ।
नकारस्य च मूर्द्धन्यस्तेन सिद्ध्यति माणवः ॥
Thus मनु + षुक् + अञ् = मानुषः \a man or man-kind\. So also मनुष्यः formed with यत् ॥ These affixes here have not the force of Patronymics, hence they are not dropped in the plural, as मानुषाः \men\. When the descendant is to be expressed, we have the affix अण् as मनु + अण् = मानवः 'son of Manu', as in मानवी प्रजा ॥ So also the word माणव, there न is changed into ण and denotes the descendant of Manu, with the sense of contempt as well as dullness implied.,