Darwinism is concerned with the creation of all life from an alleged single life form of long long ago
'Darwinism' is a loaded term. You may as well refer to gravity as 'Newtonism', relativity as 'Einsteinism' or electromagnetics as 'Amperism'.
Evolution, the scientific theory that Darwin forwarded and 10,000s of thousands of others have since modified and advanced, postulates a universal common ancestor that existed sometime around 3.5-3.7 b.y.a. This postulation is made because its what is suggested by the evidence.
Darwin was not alone in forwarding the evidence for evolution, and he may have actually been pre-empted by some other writers from 20 years earlier (of which he may or may not have been aware), but he presented the most grounded, evidentially supported version of the theory.
by only naturalistic means.
Science can only ever deal with the natural.
A scientific theory is not theistic. It is not atheistic either. It is simply a series of statements that offer the best explanation for the evidence we observe in the natural world. Just because it contradicts certain interpretations of certain religious texts, does not make it atheistic.
Creationist: "At a broad level, a Creationist is someone who believes in a god who is absolute creator of heaven and earth, out of nothing, by an act of free will.... Here, Creationism means the taking of the Bible, particularly the early chapters of Genesis, as literally true guides to the history of the universe and to the history of life, including us humans, down here on earth... Creationism in this more restricted sense entails a number of beliefs.
from the Stanford Encyclopedia of Philosophy,
http://plato.stanford.edu/entries/creationism/
Both common and specialist definitions of the term 'creationist' would appear to be in opposition to the reality of what the theory of evolution actually is.
Evolution is not a worldview. Apart from its scientific description of how life changes, evolution has no dogmas, tenants, proscriptions, beliefs or practices that anyone could associate with a worldview.
and not based on the scientific method.
Perhaps you'd like to point out, specifically and using examples, just where the theory of evolution is not based on the scientific method.
You can start with the ~37,000 papers published on 'biological evolution' this year alone, and then work backwards. Shouldn't take long.
https://scholar.google.com.au/scholar?as_ylo=2015&q=biological+evolution&hl=en&as_sdt=0,5
Remember to show your working.