Here, I examine the shape of the tree of life on Earth that is the result of four billion years of birth, death, reproduction, and relatedness. This extended family tree has been produced by four billion years of using energy from the environment to power biological systems. I then consider the question of how to define life, from both evolutionary and metabolic perspectives. Defining life is not easy, but it is possible if we accept that viruses constitute a grey area. Next, I deal with the main driver of evolution on Earth (and probably elsewhere), namely Darwinian natural selection. This driver only works when there is variation among organisms, so our next port of call is how variation arises – gene mutation and related processes. Finally, I examine the origin of life. The emphasis here is on the hypothesis that life arose here rather than arriving pre-formed from another planet – the Terraspermia hypothesis. The alternative Panspermia hypothesis is considered to be fatally flawed.