Genetic-cultural coevolution is the idea that once pre-humans acquired basic abilities for cultural learning and cumulative culture, this created a positive feedback (see Positive Feedback in Evolutionary Transitions) where culture became more sophisticated and this drove genetic evolution to create new people who could function better in the cultural environment, who created even more complex culture, and so on. The cultural/social environment quickly became a more critical determinant of individual success than the natural environment, and ever greater brainpower was required to navigate this new world.
Because this is a fairly new idea, there isn't complete agreement on what to call this phenomenon. “Dual Inheritance Theory” seems the most common, but doesn't highlight the critical feedback interaction. We prefer “genetic-cultural” to “gene-culture” for the technical reason that many important genetic changes were likely in non-coding sequences and in sexual reassortment of existing genes, rather than in mutations to genes.