Body Size

The estimation of body size among the earliest members of the genus Homo (2.4e1.5 Myr [millions of years ago]) is central to interpretations of their biology. It is widely accepted that Homo ergaster possessed increased body size compared with Homo habilis and Homo rudolfensis, and that this may have been a factor involved with the dispersal of Homo out of Africa. The study of taxonomic differences in body size, however, is problematic. Postcranial remains are rarely associated with craniodental fossils, and taxonomic attributions frequently rest upon the size of skeletal elements. Previous body size estimates have been based upon well-preserved specimens with a more reliable species assessment. Since these samples are small (n < 5) and disparate in space and time, little is known about geographical and chronological variation in body size within early Homo.

Body size is one of the most important determinants of the biology of a species, as it correlates with life history, energetic expenditure, diet, thermoregulation, and home range size, among other factors. Although the evolution of body size within the genus Homo is an important issue, the most influential large-scale studies have been performed over 20 years ago, with a recent interest in this issue only in the last few years. In the meantime, the widely accepted interpretation that there was a major shift in body size with the origin of Homo ergaster/erectus when compared Homo habilis, Homo rudolfensis, and australopithecines has come under criticism. Recent analyses have demonstrated that body size within early Homo is spatially and temporally variable, only showing significant increase in the Koobi Fora region after 1.7 Mya (Will & Stock, 2015). Broad temporal analyses of body size have highlighted the significant increase in body mass during the late Middle and Late Pleistocene (Ruff, 1997), and that brain size increases correspond closely with body mass increases throughout the Pleistocene (Grabowski, 2016). Even though new body size data is now accumulating rapidly for various parts of the hominin record (Arsuaga et al., 2015; Grabowski et al., 2015;  Will & Stock, 2015), no study comparable to the scope of Ruff et al. (1997) has since been performed.
In this paper we investigate taxonomic, spatial and temporal variation in two components of body size within the genus Homo: body mass and stature. We combine size estimates of hominin fossils from our own studies with other published data, resulting in the largest sample for a single study so far (n=319). The body size estimates cover roughly four million years (4.1 Mya – 11 ka) and derive from African, European and Asian specimens, including several genera and species of hominins. This data set allows for a detailed assessment of body size evolution within the genus Homo and relative to earlier hominins.
Analyses of the body size estimates demonstrate that: a) the origins of the genus Homo are characterized by a significant increase in body size compared to australopithecines and paranthropines, but also feature abundant spatial and temporal variation within an enlarged size range; b) members of Homo erectus/ergaster are marked by a diversification in body mass and stature rather than directional increase; c) a consistent and universal increase in body size is only established in Middle Pleistocene hominins (e.g. Sima de los Huesos, Atapuerca; Homo heidelbergensis), Neanderthals and modern humans after ca. 0.5 Mya; d) selection against smaller body mass and stature occurred in the late Early and Middle Pleistocene, and; e) there are no simple latitudinal trends in the variation of body size estimates within Middle and Late Pleistocene Homo in Europe. These results have implications for studies concerned with human dispersal and encephalization, and more generally for how we interpret the evolution and biology of our genus. In light of the above, rather than focusing exclusively on species means and unidirectional models, perspectives that emphasize spatio-temporal variability and phenotypic plasticity might be more fruitful frameworks for interpreting the evolution of body size in our genus.

Insects in diapause characteristically feed very little or not at all, thus they are largely or totally dependent on energy reserves sequestered prior to the entry into diapause. Fats are the dominant reserve used during this period, but non-fat reserves are also important for some species, especially during certain phases of diapause. Metabolic depression, coupled with the low temperatures of winter, facilitates the economic utilization of reserves during the many months typical of most diapauses. Though many insects store additional lipid prior to the entry into diapause, our review of the literature indicates that this is not always the case. We provide evidence that interactions between nutrient storage and metabolism can influence the decision to enter diapause and determine how long to remain in diapause. In addition, the energy reserves expended during diapause have a profound effect on post-diapause fitness. Though the physiological and biochemical mechanisms that regulate nutrient homeostasis prior to and during diapause remain poorly known, we propose several mechanisms that have the potential to contribute to diapause-associated nutrient homeostasis. Potential players include insulin signaling, neuropeptide F, cGMP-kinase, AMP-activated protein kinase, and adipokinetic hormone. r