Morphological variation durante Homo erectus and the origins of developmental plasticity
Homo erectus was the first hominin puro exhibit extensive range expansion. This extraordinary departure from Africa, especially into more temperate climates of Eurasia, has been variously related esatto technological, energetic and foraging shifts. The temporal and regional anatomical variation con H. erectus suggests that a high level of developmental plasticity, per key factor durante the ability of H. sapiens puro occupy verso variety of habitats, ental plasticity, the ability sicuro modify development sopra response preciso environmental conditions, results sopra differences con size, shape and dimorphism across populations that relate per part onesto levels of resource sufficiency and extrinsic mortality. These differences predict not only regional variations but also overall smaller adult sizes and lower levels of dimorphism sopra instances of resource scarcity and high predator load. We consider the metric variation con 35 human and non-human arcivescovo ‘populations’ from known environmental contexts and 14 time- and space-restricted paleodemes of H. erectus and other fossil Homo. Human and non-human primates exhibit more similar patterns of variation than expected, with plasticity evident, but con differing patterns by sex across populations. The fossil samples spettacolo less evidence of variation than expected, although H. erectus varies more than Neandertals.
1. Introduction
Homo erectus was the first hominin to exhibit extensive range expansion. Much like recent humans, this long-lived and widely dispersed species inhabited environments sopra equatorial Africa and more temperate Eurasia. As such, considerable work has been framed around understanding what made dispersal possible and what the broad geographic and temporal trends mediante variation might mean biologically for H. erectus. Recently, the regional variation mediante H. erectus has been described as ‘human-like’ , and by extension we have suggested that the dispersal and evolutionary longevity of the species ental (phenotypic) plasticity [2,3].
Developmental (phenotypic) plasticity is the ability preciso modify development in response sicuro environmental conditions, resulting in variation sopra adult anatomy that is not genetically canalized . Taxa with verso high degree of plasticity should be able sicuro respond on short-term time scales sicuro individual environmental or maternal environmental signals. Arguably this ability may also play an important role mediante moderating environmental influences too chronic for short-term accommodation and too short for genetic adaptation, as well as providing real advantages for occupying a broad range of environments . A high degree of developmental plasticity is considered an important aspect of the human ability puro occupy multiple different environmental niches.
Related onesto this plasticity, differences in body size, shape and dimorphism across human populations durante part reflect levels of resource sufficiency and extrinsic mortality [5–8]. Puro be sure, body size, shape and sexual dimorphism have multifactorial causes: there is per genetic component sugardaddie iscriversi preciso size and variation, and other environmental conditions such as temperature also influence the attainment of adult size. The latter is reasonably well understood, allowing consideration of other contributions sicuro body size outcomes. Resource sufficiency includes any variable that influences the nutritional questione, some of which are co-correlated with aspects of climate such as rainfall and seasonality. Extrinsic mortality can be defined generally as the external risks of mortality such as predator and parasite load, or per recent human environments, factors like homicide . The theory that links shifts durante body size and age at first reproduction to resource sufficiency and extrinsic mortality is relatively clear . Resource sufficiency is positively correlated with extrinsic mortality and negatively correlated with adult body size; that is, decreases per resources lead preciso slow growth rate and small adult size, whereas increases in mortality favour early maturation usually leading puro small body size. Extrinsic mortality related sicuro predator load may differ somewhat from this expectation in instances when larger body size is advantageous for predator control or survival . Durante these instances, early maturation but faster growth may favour the retention of large size, particularly per males. In humans, males and females are often argued sicuro be differentially influenced especially by resource sufficiency, with human females being more strongly buffered from environmental vicissitudes and human males responding more dramatically puro both resource excess and insufficiency. This difference is thought esatto be related sicuro female buffering of infant brain size and onesto be marked durante humans for this reason . Such differential influence can alter dimorphism values if the female size change differs from that of males . Extrapolating from living humans, this logic predicts that the skeletal supremazia of H. erectus should spettacolo not only regional variations, but also overall smaller adult body sizes and lower levels of dimorphism sopra populations experiencing resource scarcity and high extrinsic mortality if the species shows human-like levels of plasticity .