Abstract
During the evolution of hominids, childhood and adolescence have been added as new life-history phases. The transition from infancy to childhood (ICT) confers a predictive adaptive response to energetic cues that strongly influence adult height, whereas the transition from juvenility to adolescence establishes longevity and the age of fertility. Evolutionary short-term adaptations to energy crises apparently use epigenetic mechanisms that defer the ICT, culminating in short stature. The study of hunter-gatherers gives us an indication of pre-demographic transition populations and their life style that prevailed for 99% of homo's evolution. The secular trend for receding age of pubertal development has been an adaptive response to positive environmental cues in terms of energy balance. In natural fertility preindustrial societies with limited access to modern contraception and health care, and whose economies are primarily subsistence-based, most resources are invested as somatic capital in human body size and fertility. Here we review results from databases for natural fertility societies, with the information on life history, population density, height and body mass, indices of adolescence and fertility. By using them it was possible to verify the ICT model as well as to explore pubertal parameters that are related to evolutionary fitness. They confirmed that body size was adaptively smaller in hostile environments, and was tightly associated with reproductive fitness.
Highlights
We focused on natural fertility preindustrial societies, with limited access to modern contraception and health care and whose economies are primarily subsistence-based, in which most resources are invested as somatic capital in human bodies, in contrast to industrial societies, who possess more stored, inherited wealth
Based on analysis of the stature, growth, and reproductive fitness in several Pygmy tribes, they argued that their small body size is an adaptation that evolved as the result of a life history trade-off between the fertility benefits of a large body size against the risk of late growth in societies where longevity is severely compromised by a hostile environment
The infancy to childhood (ICT) model provides a framework for understanding the life-history consequences of resources and density dependence in the evolution of body size changes in humans [3]
Summary
During the evolution of hominids, childhood and adolescence have been added as new life-history phases. By using them it was possible to verify the ICT model as well as to explore pubertal parameters that are related to evolutionary fitness They confirmed that body size was adaptively smaller in hostile environments, and was tightly associated with reproductive fitness. Life history has been defined as the strategic allocation of an organism’s energy toward growth, maintenance, reproduction, raising offspring to independence, and avoiding death [1,2,3]. It is, among others, the strategy of when to be born, when to be weaned, when to stop growing, when to reproduce, and when to die in the best way as to increase fitness [4]. Bogin and Smith [1, 2] have previously reported that Homo habilis (1.9 mya) had a shorter period of infancy than his predecessors, introducing a new strategic life-history phase: childhood, characterised by initial acceleration stabilisation of growth velocity, dependence on the family and tribe beyond his mother for food provision
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
