Chimpanzee infant mortality cycles are self-organized and critical

Background/Question/Methods

Although there is growing recognition that the structures of disease contact networks have profound impacts on disease dynamics, there has been relatively little work detailing how such network structures are generated. Previously we have reported that infant chimpanzees at our study site in Cote d’Ivoire are subject to respiratory disease outbreaks and show cyclic mortality patterns similar to the cyclic disease dynamics observed in human children.

Results/Conclusions

Here we show that chimpanzee contact networks naturally self-organize towards a highly connected state: a consequence of both reproductive synchronization amongst females who lose their infants in disease outbreaks and the reliably increasing trajectory of social play by infants. Not only is this network self-organization consistent with the mechanisms described in the theory of self-organized criticality (SOC), infant deaths follow the power law frequency distribution predicted by SOC. This is the first disease study to show both pattern and mechanism of SOC and illustrates the new avenues of research that may be opened in primatology through an integration of ecological theory with behavioral and population data.