The "Origin of the Species" is not an ordinary science book. It purports to challenge the account of Creation as written in the Bible. It came from a Christian whose conclusions about observations in the natural world led him to disbelief. It proposes a theory that changes the perception of man regarding important issues like where we come from, where we are going to, what is the purpose of life, etc. As such, its repercusions involve not only Naturalism but also Philosophy, Religion, Theology, Psychology, Ethics, History, Sociology, etc.
I haven't researched the historic background of such a work but one can roughly say that it was landed at a time where there was a revival of humanistic and liberal ideas, the world was being delivered from the heritage of Catholicism, other religions established themselves as universal systems of faith, technologic advances were rapidly being implemented after centuries of stagnation, there was an Industrial Revolution taking place and a flourishing capitalist economy, the levels of worlwide commerce, information and comunication increased, etc. Men were in search of new answers to ancient questions about themselves.
The ideas of Darwin found a rich ground and became a paradigm. Science became the new religion. It's no wonder that many other fields adopted the paradigm and worked to sustain it. No human intellectual output is purely objective and Science is no exception. If you believe in Evolution you interpret reality accordingly.
For the Theory to work they needed: (1) to erase traces of an intelligent Creator, (2) a long timeline to allow gradual changes, (3) conceptions about matter and energy which came from nowhere, organised very nicely - after randomness and chaos ceased on their own - and generated the building pieces of the universe and life.
Therefore, the earth became very old and the Bible was no more than a pretentious book of myths full of allegories and metaphors.