Growth and development in the genus Pan : a life-history approach

• Main Author: Brimacombe, Conrad Stephen
• Other Authors: Nystrom, Pia ; Kuykendall, Kevin
• Published: University of Sheffield 2013
• Subjects: 930
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.605327

Comparative analysis between extant apes and modern humans has for decades been used to inform the understanding of how humans have evolved their present life-history patterns. Such studies have specifically focused on skeletal life-history as patterns of skeletal development may be represented in fossil human ancestors. Theoretical approaches to analyzing life-history have invoked the principles of heterochrony where changes in growth rate and sequences of maturational events have been proposed to explain differences between Pan and Homo. Debate has arisen as to whether humans demonstrate neoteny (retention of sub-adult features into adult form), hypermorphosis (attainment of adult form prior to complete maturation) or a mixture of both. This debate remains unresolved partly due to incomplete data for development in Pan and lack of integration of data for different skeletal sub-systems such as dental development and epiphyseal fusion. The objective of this study is to improve upon the present state of knowledge by evaluating skeletal development in a sample of Pan troglodytes and Pan paniscus from osteological collections. The sample used in this study consisted of 177 Pan troglodytes and 37 Pan paniscus individuals sourced from the Powell-Cotton Museum (United Kingdom), the Museum of Central Africa (Belgium), and the Adolph Schultz Collection at University of Zurich (Switzerland).The majority of individuals were wild-shot. Epiphyseal fusion was assessed using a method based on McKern and Stewart. Radiographs were taken for mandibular dentition. Dentition was assessed by the Demirjian method for 8 teeth. Length was measured for all long-bones. Data were analysed for three major parameters of skeletal growth, these being growth rate, sequence of maturational events, and allometric change. Comparisons between chimpanzees and bonobos found these two species to be essentially the same in terms of measured skeletal maturation parameters. Analysis of Pan paniscus was more limited due to smaller sample size. Comparison between Pan and Homo focused primarily on comparison between chimpanzees and humans due to sample size limitations for Pan paniscus. Comparisons of sequences found broad similarities between these two species in terms of epiphyseal fusion events. Comparisons of fusion sequences and dental maturation showed some differences, especially in the later stages of maturation for these two systems. Epiphyseal fusion event timing was also considered in the context of proportional change in length of long-bones. It was found that the relative timing of fusion events as proportion of growth in length was the same for both chimpanzees and humans. Estimates of chronological age of fusion were produced for epiphyses analysed in prior studies as well as additional centres not previously evaluated. This was done using Kuykendall's regression equation for 8 teeth. Estimates for age of fusion determined in this study closely matched the data for sites observed in prior studies using known-age samples. This indicates that the estimates for age for previously undocumented sites in the present study are likely accurate. The implications of these results for theoretical approaches to studying growth as well as the study of fossil hominids are discussed. Humans appear more divergent from apes when maturational events are considered in the context of chronological years. Comparisons based strictly on maturational events suggest that the differences in growth rate may distort the perception of how large differences in life-history pattern actually are.