Consider the first life form on Earth. Fragile and microscopic, it likely did not "live" for very long. Over time more and more organisms existed momentarily before ceasing to exist. Eventually one entity came into being with the ability to divide and propagate copies of itself. This meant that one piece of it could die without the entity itself being destroyed. It thereby improved it's ability to survive by spreading it's existence into multiple bodies. This entity continued to multiply and propagate, with different pieces of itself changing and mutating to be slightly different than it's siblings. Over billions of years this being split itself into billions of different pieces. With some pieces being extraordinarily different from each other in terms of size, shape, duration of existence, mechanism for reproduction, etc. We see these pieces now as the organisms that inhabit the Earth. But we no longer consider the entity that is comprised of all of Earth's organisms. I will define this being, with all of it's pieces, as Life.

It should be easy to see now that each piece (or organism) of Life plays an important role to keep Life itself alive. For example, if each and every living organism stopped reproducing, eventually Life itself would die. A simple analogy can be made to the individual cells of our body. We are able to consider the existence of a single cell, and can see the role it plays in keeping our bodies alive. If all of our cells died, we would also die. If we considered the "goal" or "purpose" of one of our cells, we may conclude it is to keep us alive. Any cell that was not functioning to further our own existence would be working towards it's own detriment, because for our body to die would mean the death of all of our cells.

With this lens, we can see evolution as technique that Life uses to improve itself. Using small amounts of genetic variation during reproduction, Life ensures that it's pieces are able to improve and adapt to a changing environment. It results in competition between members of life that results in Life as a whole improving it's ability to survive. The evolutionary pressure that resulted in the first marine lifeform to adapt to living on land can be seen as Life expanding it's domain. With this lens we can also see humanity's attempt to colonize other planets as Life's first off-world expansion.