This is one of the questions that Richard Dawkins answers in his book, The Selfish Gene. I’m reading it and thought I’d whet your appetite for reading it, too, by blogging some highlights along the way.
Chapter 1: Why Are People?
A misconception persists among the lay public that animals behave the way they do “for the survival of the species”. As we will see shortly, nothing could be further from the truth.
Chapter 2: The Replicators
Evolution did not begin with a one-celled organism. What got things underway was the chance emergence of one or more molecules that had the remarkable property of catalyzing their own replication from the surrounding prebiotic soup.
For a long time, there was enough prebiotic soup to feed all the molecules but eventually resources became scarce. At that point, competition began: the survival of the fittest molecules.
Chapter 3: Immortal Coils
As competition intensified, selection pressure forced the replication strategies to become more and more clever. Fortresses were built. Alliances were formed. Eons later, we now call the replicators genes and they navigate the world in robots that call themselves bodies.
Genes are the unit of evolution. Evolution takes place for their survival, not the survival of individual bodies, much less of entire species.