There are three reasons that cumulative cultural evolution create adaptations that are beyond the inventive capacity of individuals.
First, cultural learning can allow individuals to learn selectively. This is advantageous because opportunities to learn from experience or by observation of the world vary. For example, a rare, accidental event could provide evidence that heating some kinds of stone to the right temperature makes it much easier to knap or flake pieces to shape a blade. Such rare cues allow accurate low-cost inferences about the environment. However, most individuals won’t observe these cues and thus making the same inference will be much more difficult for them. Organisms that can’t imitate must rely on individual learning, even when it is difficult and error prone. Each individual has to independently discover that heating stone makes it easier to knap.
In contrast, an organism capable of cultural learning has options, copying when she has little reliable information, but learning individually when it’s cheap and accurate. Research has shown that selection can lead to a psychology that causes most individuals to rely on cultural learning most of the time and also simultaneously increase the average fitness of the population over the fitness of a population that does not rely on cultural information.
Second, cultural learning is advantageous because it allows acquired improvements to accumulate from one generation to the next. Many kinds of traits admit successive improvements toward some optimum. Bows vary in many dimensions that affect performance—such as length, width, cross section, taper, and degree of recurve. It is typically more difficult to make large improvements by trial and error than small ones. Thus, it is much harder to design a useful bow from scratch than to tinker with the dimensions of a reasonably good bow. A cultural learner can take advantage of the accumulated history of small improvements, while an individual learner has to start from scratch. Recently, researchers have shown that Hadza hunter-gatherers in northern Tanzania depend on excellent bows whose design they do not fully understand.