The distinction between human life and animal life therefore begins with the scientific system of varṇa and āśrama, guided by the experience of the sages in relation with the demigods, gradually rising to the summit of reestablishing our eternal relation with the Supreme Absolute Truth, the Personality of Godhead, Lord Śrī Kṛṣṇa. When God-made varṇāśrama-dharma, which is strictly meant for developing animal consciousness into human consciousness and human consciousness into godly consciousness, is broken by advancement of foolishness, the whole system of peaceful and progressive life is at once disturbed. In the age of Kali, the first attack of the venomous snake strikes against the God-made varṇāśrama-dharma, and thus a person properly qualified as a brāhmaṇa is called a śūdra, and a śūdra by qualification is passing as a brāhmaṇa, all on a false birthright claim. To become a brāhmaṇa by a birthright claim is not at all bona fide, although it may be a fulfillment of one of the conditions.
(Srimad Bhagavatam-----1:16:31-----purport).

There are three kinds of suffering, including miseries pertaining to the body and mind. In Hawaii, in front of my house, a man was keeping some animals and birds for the purpose of taking them to be slaughtered. I gave this example to my students: "These animals are standing here, and if you tell them, 'Oh, my dear animals, why are you standing here? Go away! You are meant for the slaughterhouse,' they cannot go. They have no intelligence." Suffering without knowledge, without remedy, is animal life. One who cannot understand that he is suffering and who thinks that he is very well off is in animal consciousness, not human consciousness. The human being should be cognizant of suffering the threefold miseries of this planet. One should know that he is suffering in birth, suffering in death, suffering in old age and suffering in disease, and one should be inquisitive as to how he may avoid the suffering. That is real research work.
(Easy journey to other Planets).

We have to give up this body, willingly or unwillingly. The day will come when we will have to submit to the laws of nature and give up this body. Even President Kennedy in his procession had to submit to nature's law and change his body for another body. He could not say, "Oh, I am the President; I am Mr. Kennedy. I cannot do that." He was forced to do it. That is the way nature works. The purpose of our developed human consciousness is to understand how nature works. Aside from human consciousness, there is consciousness in dogs, cats, worms, trees, birds, beasts and all other species. But we are not meant to live in that consciousness. The Śrīmad-Bhāgavatam says that after many, many births we have attained the human form of body. Now we should not misuse it. Please utilize this human life to develop Kṛṣṇa consciousness and be happy.
(Easy journey to other Planets).

A person in ignorance takes it as the usual course that days come, and after the days, the nights come. This is the law of material nature. But a man in ignorance does not know that when the sun rises early in the morning it begins to take away the balance of his life. Thus day after day the span of one's life is reduced, and forgetting the duty of human life, the foolish man simply remains in the company of his wife and enjoys her in a secluded place. Such a condition is called apakṛṣṭa-cetana, or degraded consciousness. Human consciousness should be used for elevation to Kṛṣṇa consciousness. But when a person is too much attracted to his wife and family affairs, he does not take Kṛṣṇa consciousness very seriously. He thus becomes degraded, not knowing that he cannot buy back even a second of his life in return for millions of dollars. The greatest loss in life is passing time without understanding Kṛṣṇa. Every moment of our lives should be utilized properly, and the proper use of life is to increase devotional service to the Lord. Without devotional service to the Lord, the activities of life become simply a waste of time.
(Srimad Bhagavatam-----4:27:3-----purport).

A tiger may eat meat. It is a tiger. But I am not tiger. I am human being. And if I have got sufficient grains, fruits, vegetables, and other things, God has given, why should I go to kill a poor animal? This is humanity. You are animal plus human. If you forget your humanity, then you are animal. So we are not simply animal. We are animal plus humanity. If we increase our quality of humanity, then our life is perfect. But if we remain in animality, then our life is imperfect. So we have to increase our human consciousness. That is Kṛṣṇa consciousness. That is Kṛṣṇa conscious.
(Lecture on Bhagavad-Gita-----3:11-19).

Perfection of human consciousness is there when one understands that "I am not this body. I am spirit soul." Ahaṁ brahmāsmi. That is perfection. But if you study scrutinizingly so many men, every one is bodily conscious.
(Lecture on Bhagavad-Gita-----7:1-3).