Heightened fearfulness as a developmental adaptation.

Although we find many merits to Grossmann's fearful ape hypothesis, unlike Grossmann, we see heightened fearfulness as an ontogenetic adaptation, signaling helplessness and fostering caregiving during infancy, which subsequently became exapted to promote cooperation. We also argue that, rather than being the "breeding ground" for enhanced infant fearfulness, cooperative care is more likely the evolved product of enhanced fearfulness.