Energetic consequences of being a Homo erectus female

Abstract

Body size is one of the most important characteristics of any animal because it affects a range of behavioral, ecological, and physiological traits including energy requirements, choice of food, reproductive strategies, predation risk, range size, and locomotor style. This article focuses on the implications of being large bodied for Homo erectus females, estimated to have been over 50% heavier than average australopithecine females. The energy requirements of these hominins are modeled using data on activity patterns, body mass, and life history from living primates. Particular attention is given to the inferred energetic costs of reproduction for Homo erectus females based on chimpanzee and human reproductive scheduling. Daily energy requirements during gestation and lactation would have been significantly higher for Homo erectus females, as would total energetic cost per offspring if the australopithecines and Homo erectus had similar reproductive schedules (gestation and lactation lengths and interbirth intervals). Shortening the interbirth interval could considerably reduce the costs per offspring to Homo erectus and have the added advantage of increasing reproductive output. The mother would, however, incur additional daily costs of caring for the dependent offspring. If Homo erectus females adopted this reproductive strategy, it would necessarily imply a revolution in the way in which females obtained and utilized energy to support their increased energetic requirements. This transformation is likely to have occurred on several levels involving cooperative economic division of labor, locomotor energetics, menopause, organ size, and other physiological mechanisms for reducing the energetic load on females.

Stature estimation from complete long bones in the Middle Pleistocene humans from the Sima de los Huesos, Sierra de Atapuerca (Spain)

“…Increases in body mass generate greater stresses in the pelvic region and more power is required to move the body, i.e., more muscles and therefore more energy. Total energy requirements of these archaic humans were very high (Holliday and Falsetti, 1995;Leonard and Robertson, 1997;Trinkaus and Rhoads, 1999;Sorensen and Leonard, 2001 ;Aiello and Key, 2002 ;Aiello and Wells, 2002;Franciscus and Churchill, 2002;Leonard and Ulijaszek, 2002 ;Steegmann et al, 2002 ;Churchill, 2006;Steudel-Numbers, 2006;Weinstein, 2008;Gamez-Olivencia et al, 2009), and were a crucial factor for their survival, making them subject to the forces of natural selection.…”

The energetic significance of cooking

“…The unflared, barrel shape of the thoracic cage and the narrow dimension of the pelvis in H. erectus also indicate a small gut (Aiello and Wheeler, 1995), suggesting a diet of higher digestibility. Despite these anatomical constraints, H. erectus shows signals of increased energy use compared to Homo (Australopithecus) habilis, including larger body and relative brain size (Leonard and Robertson, 1994;Ruff et al, 1997;Aiello and Wells, 2002), a suite of locomotor adaptations that improve the human capacity for long-distance running (Bramble and Lieberman, 2004), and possibly reduced interbirth intervals (Aiello and Key, 2002). The apparently softer, more digestible and higher energy diet of H. erectus is consistent with the expected effects of cooking (Wrangham, 2006).…”

“…This is not surprising, given that heat greatly facilitates the gelatinization of starch, denaturation of proteins (including collagen), and killing of foodborne pathogens. This provides a further reason why the energetic transition associated with H. erectus, which is uniquely large compared to transitions involving any subsequent human species (Aiello and Key, 2002;Aiello and Wells, 2002;Wrangham, 2006), is best ascribed to the adoption of cooking, and not solely to non-thermal processing.…”

“…Such effects could potentially yield large amounts of energy . A net rise in the energy value of the diet is theoretically important because the total size of the energy budget affects numerous aspects of evolutionary biology, including body mass, rates of growth and reproduction, defense against parasites and pathogens, and investments in locomotion (Leonard and Robertson, 1997;Ellison, 2001;Aiello and Key, 2002). If cooking provides significant amounts of energy, it can therefore be expected to have had major effects on human evolution.…”

The evolutionary roles of nutrition selection and dietary quality in the human brain size and encephalization

“…The earliest unambiguous fossil hominins, such as Australopithecus anamensis and A. afarensis, were bipedal, but still retained some aspects of arboreal lifestyles, as demonstrated by a combination of long forelimbs, curving phalanges, and barrel-shaped thorax [3]. With the emergence of the genus Homo at 2.0 mya (H. ergaster/erectus) [4], there was a marked increase in body size, mainly in females, who almost double in size compared with Australopithecine [5]. The oldest fossil evidence for Homo sapiens is from Southern and Eastern Africa, dating to about 160-250 kya [6,7].…”