Darwinian explanations only say how a random process of selection could have created a human, but they don’t tell you what the purpose of a human being is. You cannot deduce that the purpose of human life is, for example, physical survival based on a Darwinian story.
Imagine that a powerful being called the Artist decided to create another being for the purpose of self-expression, much as we create art. Call the created being the Homunculus. Rather than tinkering in the lab to make the Homunculus the Artist put a Darwinian process in motion. The end result was a human being. However the purpose of that human being was not survival — it was self-expression.
Also – we are the Artist and the Homunculus!