RESUMEN
Cooking is a human universal that must have had widespread effects on the nutrition, ecology, and social relationships of the species that invented it. The location and timing of its origins are unknown, but it should have left strong signals in the fossil record. We suggest that such signals are detectable at ca. 1.9 million years ago in the reduced digestive effort (e.g., smaller teeth) and increased supply of food energy (e.g., larger female body mass) of early Homo erectus. The adoption of cooking required delay of the consumption of food while it was accumulated and/or brought to a processing area, and accumulations of food were valuable and stealable. Dominant (e.g., larger) individuals (typically male) were therefore able to scrounge from subordinate (e.g., smaller) individuals (typically female) instead of relying on their own foraging efforts. Because female fitness is limited by access to resources (particularly energetic resources), this dynamic would have favored females able to minimize losses to theft. To do so, we suggest, females formed protective relationships with male co-defenders. Males would have varied in their ability or willingness to engage effectively in this relationship, so females would have competed for the best food guards, partly by extending their period of sexual attractiveness. This would have increased the numbers of matings per pregnancy, reducing the intensity of male intrasexual competition. Consequently, there was reduced selection for males to be relatively large. This scenario is supported by the fossil record, which indicates that the relative body size of males fell only once in hominid evolution, around the time when H. erectus evolved. Therefore we suggest that cooking was responsible for the evolution of the unusual human social system in which pair bonds are embedded within multifemale, multimale communities and supported by strong mutual and frequently conflicting sexual interest.
RESUMEN
We recorded 'pant-hoot' vocalizations from male chimpanzees, Pan troglodytes, housed in two captive facilities in the U.S.A., Lion Country Safari and North Carolina Zoological Park. Acoustic analysis revealed significant differences between the two groups in the temporal patterning of the calls. Because the captive males within each group are from diverse origins, within-group similarity in pant-hoot structure could not have resulted from genetic similarity of the callers. In addition, there were no obvious differences in housing conditions that could have caused the between-group differences. Instead, the results suggest that the calls in each group converged in structure as a consequence of vocal learning. Within-group variation in call structure of the captive groups was similar to that found in a group of wild Ugandan chimpanzees (Kanyawara study group, Kibale National Park), suggesting the presence of species-specific constraints on this call within which different populations can converge on local variants. In addition, an acoustically novel pant-hoot variant that was introduced by one male to the Lion County Safari colony spread to five other males in the same colony. This suggests that chimpanzees may also be able to modify the frequency parameters of their calls through learning. Copyright 1999 The Association for the Study of Animal Behaviour.
RESUMEN
This study explored some aspects of chimpanzee social behaviour using mitochondrial DNA sequence data as an index of matrilineal relatedness. The hypothesis tested was that matrilineal relatedness predicts social affiliative preference in wild chimpanzees. Several behavioural measures of individual social preference were examined for chimpanzees from Kanyawara community in Uganda's Kibale Forest. None of the four pairs of strongly affiliative males in this community could have been maternal brothers, since no pair shared the same mitochondrial DNA sequence. Fourteen chimpanzee communities outside Kibale, for which no direct behavioural data were available, were also studied by using communal nesting as a rough index of affiliative preference. Again, chimpanzees that nested together did not tend to be matrilineally related. The results suggest that kin selection is weaker than previously thought as a force promoting intra-community affiliation in chimpanzees.1997The Association for the Study of Animal Behaviour
