Artificial Intelligence is about designing and constructing artefacts, normally not about explaining human intelligence. So, why should we care about natural intelligence when talking about AI? There are several important more or less recent findings in brain science as well as ethology which require a deeper rethinking on the AI side. Based on them, the hypothesis in this talk is: The rising complexity of the behaviour system and of personalized social relationships was one of the major reasons for developing intelligence - contrary to the huge resource consumption that intelligence costs an individual. The most important result of this development was the capability of forecasting the behaviour of conspecifics for survival in a complex social environment. This capability was also useful for other purposes, including forecasting behaviour of individuals of other species and nature itself.