However, the apparent lack of an adolescent length-GS in non-human primates despite often pronounced weight-GSs may largely reflect a methodological problem that results from scaling issues when comparing length and weight growth rates ( Cullen et al., 2021 Schmidt-Nielsen, 1984). This is puzzling, because adolescent GSs in body weight occur in many primate species, including humans ( Leigh, 2001). There is wide consensus that the human adolescent growth spurt (GS) in body length is evolutionary unique and absent in other primates ( ( Bogin, 2021 Gluckman et al., 2013 Hochberg, 2012 Holmgren, 2022 Stevens et al., 2013 Stulp and Barrett, 2016), but see ( Ellison et al., 2012 Watts and Gavan, 1982 Weisfeld, 2006)). This work will be of interest to human evolutionary biologists, primatologists, and researchers studying the ontogeny and evolution of growth and development in general.

The results are solid, based on the largest sample ever considered in the study of bonobo growth and include both morphometric and endocrinological data. This valuable paper sheds new light on the growth trajectory of bonobos ( Pan paniscus), with explicit contributions to discussions of the exclusivity of certain aspects of growth in modern humans, most specifically with respect to components of the adolescent growth spurt, which may be less human-specific among primates than presumed to this point. Altogether, our results emphasize the importance of considering scaling laws when interpreting growth curves in general, and further show that pronounced, human-like adolescent length-GSs exist in bonobos and probably also many other non-human primates. We further re-interpreted published data of non-human primates, which showed that aligned GSs in weight and length exist not only in bonobos. Weight and length growth trajectories corresponded with each other and with patterns of testosterone and IGFBP-3 levels, resembling adolescent GSs in humans. We found pronounced GSs in body weight and length in both sexes. We then apply a scale-corrected approach to a comprehensive dataset on 258 zoo-housed bonobos that includes weight and length growth as well as several physiological markers related to growth and adolescence. We first outline how scaling issues and inappropriate comparisons between length (linear) and weight (volume) growth rates result in misleading interpretations like the absence of length-GSs in non-human primates despite pronounced weight-GSs, or temporal delays between length- and weight-GSs. However, this distinction between present and absent length-GSs may reflect a mathematical artefact that makes it arbitrary. Adolescent growth spurts (GS) in body length seem to be absent in non-human primates and are considered a distinct human trait.

Chimpanzee hand bones