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answers:
MARK say: Your question is unsurprisingly vague. Do you mean that the majority of people who accept evolution are atheists? Alternatively, your question might be asking why only a majority of atheists support evolution rather than all atheists.
I suspect that the majority of people who accept evolution might be atheists because many atheists think for themselves and are not told what to think. A lot of Christians reject evolution and are taught evolution is wrong by their minister contrary to the official teachings of their own denomination. All mainstream Christian denominations accept evolution.
If we take the entire world more people follow a religion and some creation myth because they know no better. They have for many reasons been deprived of education. It is not amazing that the majority of atheists are well educated. Learning to think for yourself is invaluable. When people acquire critical thinking skills they quickly reject the superstitious nonsense of religion. In saying this I make no claim that atheists are more clever than other people. Being clever is a different matter. Education is what atheists tend to have whereas the majority of the world's population are denied it.
The reason why not all atheists accept evolution is because they are not all interested in it. An all too common mistake made on this forum is to treat atheism and science as if they were synonyms, which they are not. Many think (or probably do not think and therein the problem lies) that all atheists are interested in science. This is not at all true. An atheist may be musically talented and music may be their life. They probably never give a moment's thought to evolution or any other area of science. This is not because they have seriously thought about evolution, considered the evidence and arrived at the conclusion it is false. They simply have not studied, thought about or considered the subject.
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