There are two different meanings of the word 'evolution' being used - and confused - in this thread. One of them is short for "the theory of evolution", the other points to the phenomenon of evolution itself. What Joseph is asking is whether evolution as a phenomenon is ubiquitous in the universe, or else confined to just our own planet Earth. That is a legitimate question to which the answer is not (yet) known.
However, evolution in the other sense, i.e. as the theory that explains the phenomenon, may be of some assistance in trying to get a glimpse of the answer to Joseph's question, in the following way.
The theory of evolution effectively states that if certain conditions are met, then logic dictates that evolution (as a phenomenon)
must take place. The necessary conditions are: imperfect replication and limited resources. So Joseph's question boils down to whether or not these conditions hold anywhere else in the universe besides Earth.
Although it is not yet certain whether or not evolution as a phenomenon takes place on other planets, if logic itself applies everywhere in the universe, evolution as a logical consequence of the necessary conditions is indeed "a constant" in the universe. (Let's not bicker about Joseph's peculiar use of the word 'constant'.)
This means that wherever there are imperfect replicators of any form in an environment of limited resources, the process of evolution is an inevitable consequence. Since we have no reason to assume that our planet is a special place in the universe, it is not at all unlikely that conditions such as on Earth could be found elsewhere in the universe. With billions of galaxies to search, it is indeed almost a certainty.
"Ignorance more frequently begets confidence than does knowledge: it is those who know little, not those who know much, who so positively assert that this or that problem will never be solved by science." - Charles Darwin.
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