What is Culture?
I think that the biggest revelation for me in Pinker's book The Language Instinct was the fact that groups of people thrown together without a common language spontaneously invent one. This is true even for deaf children who can't speak or hear - they invent a sign language. It only takes about a generation, but the invented language is full featured, richly expressive, and internally complete.
It appears that the same is true of culture. When Zora Neale Hurston went back to her birthplace to anthropologically investigate her fellow southern blacks, the prevailing anthropological wisdom was that the culture they had consisted of broken fragments of their ancestral African cultures jumbled together with modern white culture. The reality was richer and more complex. In fact they had created a rich and complete culture of their own, woven, to be sure, partly from strands of half remembered fragments from hundreds of different African cultures and the modern white culture in which they were embedded, but complete with its own traditions, stories, and inventions. Moreover, it was clear that that culture was rapidly evolving, mostly under the impetus of its own inventions.
Other examples accumulated once anthropologists learned to look.
It seems clear that there is a cultural instinct must like the language instinct. This shouldn't really surprise, since language is one of the biggest components of culture.
(Notes for a review of Gods of the Upper Air: How a Circle of Renegade Anthropologists Reinvented Race, Sex, and Gender in the Twentieth Century by Charles King