Many predators locate resources in environments in which sensory signals are rare, noisy, and lack directional information, and there is evidence (also from mathematical models) that a strong signal leads a searcher to concentrate their search effort near the targets [5]. Experimental data inferred from animal studies suggest that olfactory hunting is a widespread phenomenon in many predatory mammals [6]. Evaluation of fecal odorgrams by complex gas chromatographic and mass spectrometric analysis of both ancient and recent human fecal samples has revealed that human feces are rich in volatile compounds [7, 8], likely to be individuated by smell by potential predators. Indeed, paleoanthropological excavations suggest that this might have been the case, due to the high predation risk for hominids posed by large carnivores sharing the same habitats [9]. Thus, learning to control defecation could have represented a form of protection from predators.

On the other hand, the reverse reasoning is similarly intriguing. In fact, considering the remarkable pathway taken by hominids, especially concerning foraging strategies [10], one wonders whether the voluntary control of defecation may have been one of these strategies. Once again, we must rely on experimental animal models that, in this respect, appear very interesting.

In fact, many animal species undergoing predation show specific adaptations that allow recognition and avoidance of as well as defense against predators, and for many mammalian species, this includes sensitivity toward predator-derived odors [11]. Indeed, predator recognition and avoidance are important behaviors in allowing prey to mitigate the impact of their predators [12], and there is evidence that volatile compounds isolated from feces are involved in risk assessment behavior and the neurobiology of fear [13]. Thus, predators’ odors (among which the fecal ones are particularly effective) may alert the possible prey and limit the success of a predator. This fact has been confirmed in experimental settings, in which prey persistently avoid territories marked by predators’ fecal scent [14].