How Did Human Culture Evolve?

Source: Wikipedia
If culture and tradition is defined as any behavior that is learned by observing or interacting with others, then animals have culture, too. But to what degree was human cultural development due to the same causes as animal's and when did it mestasize due to our superior brains?

I believe that the additional variable is imagination. We have it; animals don't. Before Homo-sapiens, previous man species (Neanderthals, Rhodesiensis) had developed the ability to make and use stone axes. In fact, axes were in use for a million years - but without new inovations. At some point, people had to have imagination in order to take culture to the next level.

Recently, I came across this article in Live Science. It says, that much research needs to be done to trace the effects of language and intelligence on human culture.
Quote:

"We really know very, very little about the kind of roots of culture, and the biological origins of culture, and how the forms of culture we see in our species are similar to or different from those seen in animals," said zoologist Alex Thornton of Cambridge University.

Don't dismiss this question too fast. I wonder why there was no explosion of culture before the last Ice Age, a little over 70,000 years ago, when the Earth and the species of Man was much like it is today.