Hominids took to frugivory on later occasions within their history, for example, but a folivorous initial phase might explain why they have the teeth that they do (the incisors are relatively small, the canines are shortened, there are crushing surfaces on the premolars, enamel wrinkling is present on the molars, and so on), why the front of the face is reduced, and why the lower jaw has such a large and vertical ascending process, a big section adjacent to the molars and a broad but short condyle (Sarmiento 1995). A folivorous heritage could also help explain why hominids are relatively slow growing, resistant to many poisons toxic to other mammals, and equipped with an ability to make loud, complex calls. It would appear, however, that pre-hominids were not as specialised for folivory as are cautious climbers like sloths, since hominids never evolved a complex stomach and always maintained good terrestrial abilities.

Was Sarmiento right about cautious climbing and folivory being all that important in primates close to the ancestry of later hominid lineages? This isn’t an area that’s been all that intensively discussed but – when comments on ‘pre-hominid’ evolution have been provided – authors have tended not to state special preference for the idea, at least considering it as likely as suspensory behaviour or generalised climbing (e.g., Pilbeam & Young 2004, Begun 2016). Richmond et al. (2001), however, noted that ideas positing antipronograde climbing postures were “[a]rguably the most popular [of evolutionary models pertaining to pre-hominid lifestyle] … during the last several decades” (p. 81) and argued that the anatomy and biomechanics of extant hominids are consistent with an arboreal climbing ancestry. They didn’t specifically have cautious climbing and/or folivory in mind though.