Early hominids may have been weed species

Abstract

Panid, gorillid, and hominid social structures appear to have diverged as dramatically as did their locomotor patterns as they emerged from a late Miocene last common ancestor (LCA). Despite their elimination of the sectorial canine complex and adoption of bipedality with its attendant removal of their ready access to the arboreal canopy, was able to easily invade novel habitats after florescence from its likely ancestral genus, Ardipithecus sp. Other hominoids, unable to sustain sufficient population growth, began an inexorable decline, culminating in their restriction to modern refugia. Success similar to that of earliest hominids also characterizes several species of macaques, often termed "weed species." We here review their most salient demographic features and find that a key element is irregularly elevated female survival. It is reasonable to conclude that a similar feature characterized early hominids, most likely made possible by the adoption of social monogamy. Reduced female mortality is a more probable key to early hominid success than a reduction in birth space, which would have been physiologically more difficult.

A neurochemical hypothesis for the origin of hominids

“…Ardipithecus displays evidence of the simultaneous elimination of the sectorial canine complex and adoption of upright walking. Its likely descendant, Australopithecus, exhibits unusual demographic success (15). As outlined here, each of these is strikingly consistent with pivotal changes in the cortico-striatal reward pathway and striatum (Fig.…”

“…Thus, transitional, facultatively bipedal hominids were likely to have been exceptionally easy targets for predation. Despite these relatively immense disadvantages, the likely immediate descendant of Ardipithecus, Australopithecus, erupted into geographic abundance, readily spreading into novel ecological niches throughout much of Africa (15). Together, these data collectively imply that reduced intrasocial aggression, dedicated carrying behavior, and unusual demographic success occurred together in a hominoid whose life history strategy was also hampered by a need for unusually intense parental care and thus prolonged birth spacing (i.e., a K strategist).…”

“…great benefit in food searches by males. Alloparenting may have become more prevalent and would have also improved female survivorship (15).…”

“…In conclusion, we have argued here that once established, selection would have favored further amplification of the DDS personality style in the descendants of Ardipithecus and that greater sensitivity to social cues would eventually have facilitated even more intensive conformity behaviors and altruism. Both would have enhanced parenting, further decreasing interbirth intervals and especially reducing offspring mortality (15). Positive feedback from the increased social competence that it would have provided would have also increased cognitive and behavioral flexibility as well as fostered facial expressions as mechanisms of communication.…”

“…However, Holloway (5)(6)(7)(8)(9)(10)(11) argued decades ago that brain reorganization and not mere cortical volume must have been critical to the emergence and success of early hominids (here defined as humans and their ancestors following separation from the Pan clade) and that this restructuring was likely coincident with other unique features such as upright walking and canine reduction. Indeed, hominid success compared with that of all other hominoids suggests that intensified social behavior must have underlain their numeric and taxonomic spread into uniquely inhospitable environments even though other hominoids remained restricted to Miocene refugia (12)(13)(14)(15)(16)(17). What adaptations could have so remarkably favored these ancestors, and most critically, how did their social behavior eventually promote the adoption of articulate speech, empathy, and altruism through simple, individual reproductive success?…”