The life strategy of Arfak Tribe based on craniofacial shape, growth rate, and sexual maturation

Abstract

Arfak tribe is one of traditional tribes living in Manokwari, West Papua Province. The tribe has an unique natural life differently with other tribes in Indonesia. The nature of a life cycle is a result of an adaptive response of the organism to the environmental conditions that reflect to the phenomenon of evolution of bio-culture and natural selection. The research concerned to the potential evolution characters was divided into three parts. The first study discussed the diversity of craniofacial shapes of Arfak tribe in Manokwari, West Papua Province, based on 26 landmark frontal side and 16 landmark lateral side of face. Distribution individual in morphology space first five RW components have ellipsoidal pattern distribution. This means face variability relatively heterogen and polarized. The second study discussed a cross-sectional study of body size growth patterns of Arfak children and adolescents aged 6-23 years for boys and aged 6-19 years for girls. Growth rate of body weight of Arfak children at juvenile phase tend to faster than that of other population. The strategy of faster growth during juvenile phase is as a manifestation of unstable environmental condition. One of unstable environment conditions is a risk of death caused by diseases. The most common diseases suffered by children in West Papua is malaria diseases. The third study reviewed a cross-sectional study of the age at menarche and age at spermarche among the Arfak children, and the association between somatic maturation and gonad maturation. We found that median age at menarche of Arfak girls is 12,2 years, while median age at spermarche is 13,6 years. A possible factor causing young age at menarche is due to adaptation to unstable environmental conditions because of high risk of death by malaria disease in childhood. The events of menarche and spermarche achieved one year after the peak of body height velocity, and just before or at the same time with the time of maximum growth rate of body weight, body mass index, and body fat. Boys and girls accumulate body fat before puberty to be used as an energy reserve for the occurrence of gonad maturation. BF growth rate reached the lowest point at the age 16 years old, and then increase linearly with age until adulthood showed the adiposity rebound post-spermarche phenomenon. Based on these three aspects, namely smaller body size, younger age at menarche, and rapid growth rate of body weight at juvenile phase, Arfak tribe show fast life history strategy in an unstable environment. Malaria disease is a main factor of unstable environment which play a role in generating the adaptive response. On the other hand, the diversity of craniofacial since ancient still exist until now and do not show a unique typology as the three characters previously mentioned.