Some ideas from the book:

Things prefer persistence, replication can help persistence, evolution (from copying errors or otherwise) is an inevitable consequence of replication. Our bodies are vehicles for our genes to use to create more copies of themselves. A gene may favor helping a sibling or another relative at times because siblings, parents, and offspring are all just as likely to contain the same gene within them. All replicants share certain properties and memes are an interesting example of these gene-like properties.