Early hominids may have been weed species
Earliest hominids demonstrate major differences from fundamental behaviors typical of other primates. These included upright walking, a reduction in canine dimorphism, and unusual demographic success. All three were likely parts of a comprehensive adaptive complex that was also unlike that of any other primate and likely reflect a novel social structure. When primate “weed species,” such as some macaques, are examined for those key behavioral features most responsible for their unusual great demographic success, an irregular but robust elevation of female survivorship emerges as key. It is likely that a similar adaptation characterized earliest hominids such as Australopithecus.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, Australopithecus 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.