JOHN Edwards (Letters, May 1) says that for a theory to be scientific it has to explain all the facts and then challenges proponents of the theory of evolution to explain "where a cosmic egg came from."

I do not know where Mr Edwards has acquired the idea that a single scientific theory has to explain all the facts, as it is accepted within science that a scientific theory is generally a partial explanation of some aspects of nature.

It is not required that evolution explain how the universe started. If Mr Edwards still maintains that a theory has to explain all facts to be scientific, perhaps he would care to use Newton's theory of gravity to explain why water expands when it freezes or Einstein's theory of relativity to explain why heat tends to go from a hot place to a cold place?

Neither of these two theories deals with these phenomena, so, according to Mr Edward's argument, we should not regard them as scientific theories. Darwin's theory of evolution is about living creatures and is nothing to do with the origins of the universe.

PAUL ALMOND, Beechwood Cottages, Roman Road, Blackburn.