Culture seems to me like another form of tribalism, and as social creatures it comes very easily to us. We seek out people who are like us in any number of ways, and celebratory rituals where everyone gets to take part can be a very powerful way to bond and bring the group together. I've never celebrated Christmas (or any other holiday) but I have always enjoyed the atmosphere that it creates during an otherwise cold, wet, dark and dreary time of year.
"Well, evolution is a theory. It is also a fact. And facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world's data. Theories are structures of ideas that explain and interpret facts. Facts don't go away when scientists debate rival theories to explain them. Einstein's theory of gravitation replaced Newton's in this century, but apples didn't suspend themselves in midair, pending the outcome. And humans evolved from ape- like ancestors whether they did so by Darwin's proposed mechanism or by some other yet to be discovered."
-Stephen Jay Gould
-Stephen Jay Gould