Morphological variation mediante Homo erectus and the origins of developmental plasticity
Homo erectus was the first hominin to exhibit countrymatch iscriversi 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 durante H. erectus suggests that verso high level of developmental plasticity, verso key factor sopra the ability of H. sapiens sicuro occupy per variety of habitats, ental plasticity, the ability esatto modify development durante response preciso environmental conditions, results per differences in size, shape and dimorphism across populations that relate con part preciso 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 in instances of resource scarcity and high predator load. We consider the metric variation sopra 35 human and non-human primate ‘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 sopra differing patterns by sex across populations. The fossil samples esibizione less evidence of variation than expected, although H. erectus varies more than Neandertals.
1. Introduction
Homo erectus was the first hominin sicuro exhibit extensive range expansion. Much like recent humans, this long-lived and widely dispersed species inhabited environments per 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 con variation might mean biologically for H. erectus. Recently, the regional variation in 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 to modify development con response esatto environmental conditions, resulting per variation mediante adult anatomy that is not genetically canalized . Taxa with per high degree of plasticity should be able to respond on short-term time scales preciso individual environmental or maternal environmental signals. Arguably this ability may also play an important role durante 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 . Verso high degree of developmental plasticity is considered an important aspect of the human ability onesto occupy multiple different environmental niches.
Related sicuro this plasticity, differences per body size, shape and dimorphism across human populations sopra part reflect levels of resource sufficiency and extrinsic mortality [5–8]. Esatto be sure, body size, shape and sexual dimorphism have multifactorial causes: there is a genetic component esatto 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 onesto body size outcomes. Resource sufficiency includes any variable that influences the nutritional affatto, 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 mediante recent human environments, factors like homicide . The theory that links shifts durante body size and age at first reproduction puro 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 mediante resources lead puro slow growth rate and small adult size, whereas increases per mortality favour early maturation usually leading puro small body size. Extrinsic mortality related to 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 mediante males. Per humans, males and females are often argued esatto be differentially influenced especially by resource sufficiency, with human females being more strongly buffered from environmental vicissitudes and human males responding more dramatically onesto both resource excess and insufficiency. This difference is thought sicuro be related sicuro female buffering of infant brain size and puro be marked sopra 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 superiorita of H. erectus should esibizione not only regional variations, but also overall smaller adult body sizes and lower levels of dimorphism per populations experiencing resource scarcity and high extrinsic mortality if the species shows human-like levels of plasticity .
