We are part of the Tree of Life, some say is it four or five million years old and it will continue to grow much longer. Humans are at the Top of the at the moment, as out ancestors were in the past and our decedents will be in the future.

All that we are, we owe to our Predecessors, for we are part of them, just as our Decedents will be part of us. In that way, we have a kind of Immortality, in that our part in it will shape all things to come. And if we Improve our part of The Tree of Life, Leaving the World better than when we found it, Than our existence will have made a difference and nurtured our part of the Tree of Life and made a difference for all times.

The nature of Life is quite complicated and diversity and symbolic relationships between species of life on earth is really amazing.
There are two main views on this: 1 - The theory that spontaneous generation occurred as a result of random combination of chemical compounds which formed in a Primordial Pools and evolution and biological forces resulted the diversity of organisms. This can be explained by fossils of our ancestors and sciences such as Paleontology, taxonomy and Phylogeny.
2 - The theory that some universal intelligence (Call it God) has guided events that resulted in The Tree of Life.

In any case, life is something special and not to be taken lightly and we should make the best of the life we are given.