The Supreme Personality of Godhead, expanding His own potency, māyā-śakti, created innumerable species of life to house the conditioned souls. Yet by creating the forms of trees, reptiles, animals, birds, snakes and so on, the Lord was not satisfied within His heart. Then He created human life, which offers the conditioned soul sufficient intelligence to perceive the Absolute Truth, and became pleased.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
सृष्ट्वा पुराणि विविधान्यजयाऽऽत्मशक्त्या वृक्षान् सरीसृपपशून् खगदंशमत्स्यान् । तैस्तैरतुष्टहृदयः पुरुषं विधाय ब्रह्मावलोकधिषणं मुदमाप देवः
sṛṣṭvā purāṇi vividhānyajayā''tmaśaktyā vṛkṣān sarīsṛpapaśūn khagadaṃśamatsyān | taistairatuṣṭahṛdayaḥ puruṣaṃ vidhāya brahmāvalokadhiṣaṇaṃ mudamāpa devaḥ
SB 11.9.28