There are 8,400,000's of different species of life. Aśītiṁ catura. Aśītim means eighty, and catura means four. Eighty-four, lakṣāṁs, 100,000. Jīva-jātiṣu, there are different species of life. They are developing. Because after devastation, the whole universe is filled up with water. So in the water the first living beings are the fishes or the aquatics. Then that fish or aquatic means a living entity embodied by that fish body. Just like we are now, every one of us . . . I am also a soul, you are also a soul. We are embodied by this body, human form of body. Similarly, we had to accept the body of a fish. Because we are in this material world, when there is water only, where shall we go? We must live here in this material . . . unless we are liberated, we must have to live . . . and according to the circumstances, we get different types of body.
So from the aquatics, next promotion is birds, beast . . . I mean to say trees, plants, then insects, then birds, then beasts. In this way, after million, millions of years . . . you have seen that a tree is standing for thousands of years. If I get a body of a tree, then I'll have to stand in one place for many thousands of years. Therefore when you come by gradual evolution in the different species of life, by nature when you come to this point, to possess a human form of body, it is very, very rare. That is described: durlabhaṁ mānuṣaṁ janma. Durlabham. Duḥ means difficult, and labha means gain. Durlabhaṁ mānuṣaṁ janma tad apy adhruvam (SB 7.6.1). Adhruvam. He said, durlabhaṁ mānuṣaṁ janma tad apy adhruvam arthadam. Although it is also temporary. We shall not live forever with this body. The animals also, they'll also not live forever. The body will be finished after certain period of time.
So he says, Prahlāda Mahārāja says: "My dear friend, this body, this human form of body, is very, very rarely we have obtained it. Although it is temporary, but there is a great gain."