Article pp.101-109 du Vol.27 n°3-4 (2015)

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NOTE /NOTE

The significance of changes in body mass in human evolution

L’importance des changements de la masse du corps dans l’évolution humaine

T.W. Holliday

Received: 16 April 2015; Accepted: 14 July 2015

AbstractBody mass changes in the Hominini are examined from an evolutionary perspective. Among the conclusions drawn from this examination are the following: 1.) hominids (sensu lato) are among the largest and most terrestrial primates; 2.) earlyHomois on average larger in size thanAus- tralopithecus(although the two taxa do show some size over- lap); 3.) following its emergence in the early Pleistocene, Homo shows a steady increase in body mass, reaching its maximum near the end of the middle Pleistocene; 4.)Homo subsequently decreases in size throughout the late Pleistocene and into the Holocene, only to increase in size again very recently (the so-called“secular trend”); 5.) body mass variation among humans today tends to follow well-known ecogeographical“rules”, which are empirical observations with multiple potential theoretical explanations.

KeywordsBody size ·Australopithecus·Homo· Bergmann’s rule

RésuméLes changements de la masse corporelle des Homi- nini sont examinés dans une perspective évolutive. Les conclusions de cette étude sont : 1.) les hominidés (lato sensu) sont parmi les primates les plus grands et les plus terrestres ; 2.) les premiers membres du genreHomosont en moyenne plus grands que les membres du genre Australopithecus ; 3.) la masse corporelle dans le genre Homo augmente du Pléistocène inférieur au Pléistocène moyen, pour atteindre un maximum ; 4.) puis, il y a une baisse de la masse corporelle du Pléistocène moyen à l’Holocène, sauf pour la récente aug- mentation de la masse corporelle en raison de la « tendance séculaire » mondiale ; 5.) la variation de la masse du corps parmi les groupes humains d’aujourd’hui montre une tendance à suivre la règle de Bergmann, une observation empiri- que qui a plusieurs explications théorétiques potentielles.

Mots clésTaille corporelle ·Australopithecus·Homo· Règle de Bergmann

Introduction

Body mass is the most significant measure of any animal’s size and is one of the most important variables in any species’biology, as it impacts an animal’s physiology, growth and development, diet, locomotor and ranging behavior, and ultimately, its ecology [1-4]. In this light, evolutionary changes in fossil hominin body size and differences in body mass among extant humans are of particular interest to biological anthropologists, because they provide insight into potential selective regimes and patterns of behavioral ecology of humans past and present. In this review, a syn- thetic approach to hominin body size is taken, bringing recent data (both paleontological and neontological) to bear on changes in hominin body mass from the Miocene to the present. The topics to be discussed (in chronological order) are: 1.) body size of the Miocene hominoids and its implications for the hominids (sensu lato); 2.) potential body size differences between AustralopithecusandHomo, the latter of which is presumed to have evolved from the former;

3.) evolutionary shifts in body size inHomofrom the early Pleistocene to the present; and 4.) global differences in body mass among human populations today.

Body mass in the Miocene Hominoidea

The Order Primates is largely an arboreal taxon, with the vast majority of primate species spending a significant amount of time in trees [5]. This fact impacts primate body size, since arboreal mammals tend to be smaller than terrestrial mammals, as their body weight tends to be supported on smaller substrates, such as terminal branches [6]. A second important reason arboreal mammals are small is that due to momentum (= mass x velocity), falls from a height are much more dangerous for a larger animal than a smaller one. In this

T.W. Holliday (*)

Department of Anthropology, Tulane University, 101 Dinwiddie Hall, 6823 St. Charles Avenue, New Orleans LA 70118, USA

e-mail : thollid@tulane.edu DOI 10.1007/s13219-015-0133-6

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light, it is noteworthy that the largest arboreal mammal today is a primate, the orangutan (Pongo), which tends to remain extremely cautious while moving through an arboreal sub- strate [7], testing the stability of vines before transferring its weight to them, and using all four limbs for support (quadru- manous locomotion).

Given the trend for terrestrial mammals to be larger in size than arboreal mammals, it is noteworthy that the African hominids (sensu lato) today include the largest primates and also the most terrestrial. When viewed through this lens, then, it is perhaps unsurprising thatAustralopithecus is characterized by major adaptations to terrestrial bipedality [8,9]. It is important to remember that humans are not uniquely terrestrial among the hominids; rather, the difference is one of increased frequency of terrestrial behavior, instead of a qualitative difference from the African apes.

It is also possible, perhaps even likely, that increased ter- restriality among hominins and the African great apes ultimately had its roots in the overall drying trend in the late Miocene that resulted in the expansion of grasslands across much of Africa [10]–although this idea is disputed [11]. In this light, it is of interest that hominids today are on average larger in body size than Miocene hominoids (Tables 1, 2;

Fig. 1). Figure 1 contains boxplots of estimated body mass in Miocene hominoids compared to mean body mass of extant hominid (sensu lato) taxa, and shows that with the notable exception of the large-bodiedGigantopithecus bilaspurensis, the modern-day hominids tend to be larger in body size than the Miocene hominoids. At-test between the two groups is significantly different at the 0.01 level (one-tailedt=–2.546, P= 0.0075).

Body mass of Australopithecus vs. Homo

Following the 1984 discovery of the Nariokotome KNM- WT 15000 juvenileHomo erectus skeleton, it was widely believed for almost two decades that hominins achieved larger, more modern human-like body size with the emergence ofHomo erectusca. 1.6 million years ago, and that earlier hominins such as the australopiths and H. habilis were, in contrast, much smaller than people today [26-29].

Recent discoveries have called this view into question and suggest a more complicated pattern of body size evolution in hominins in general and the genusHomoin particular. First, the 1980s view of small-bodied australopiths was largely based on the diminutive, but 40% complete A.L. 288-1

“Lucy”Australopithecus afarensis specimen. More recent discoveries of additional Au. afarensis specimens [8,30]

demonstrate that“Lucy”is among the very smallest members of her species and genus (Fig. 2). Therefore, the fact that the best-preserved Au. afarensis specimen was not appar- ently drawn from the middle of the species’size distribution

may have impeded our understanding of hominin body size increase in the Pliocene and Pleistocene.

Similarly, the discussion of body size inHomo habilishas focused almost exclusively on O.H. 62, the fragmentary specimen sometimes referred to as “Lucy’s Child”[31]. It has already been pointed out that the body size and proportions of this specimen are nearly impossible to assess [32], but there is an even bigger problem with using the specimen to discuss body size of early Homo. Specifically, O.H.

Table 1 Body mass estimates, Miocene hominoids /La masse corporelle (estimée), hominoïdes du Miocène.

Taxon Body

Mass (kg)

Bones used in estimate

Reference

Oreopithecus bambolii

32 postcranial skeleton

12 Pliopithecidae

(sp. indet.)

8.7 R M³ 13

Hispanopithecus laietanus

29.9 L ulna 14

Pierolapithecus catalaunicus

32.5 n/a 15

Dryopithecus fontani

47 femur; humerus 15 Khoratpithecus

piriyai

75 R and L M1 16

Afropithecus turkanensis

34.25 n/a 17

Sivapithecus indicus(Female)

21.25 L humerus; L tibia; R calcaneus; L navicular

18

Sivapithecus indicus(Male)

41.25 R capitate; L ectocuneiform

18 Sivapithecus

parvada

65.5 postcranial size 19 Morotopithecus 43.8 multiple

elements

20 Nacholapithecus

kerioi

22 n/a 21

Gigantopithecus bilaspurensis

150 n/a 22

Equatorius africanus

30 n/a 23

Turkanapithecus kalakolensis

10 n/a 23

Ardipithecus ramidus

51 capitate; talus 24 Orrorin

tugenensis

34.4 femoral head 25

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62 was referred toHomodue to its facial similarities with the South African specimen StW 53, which some workers have referred toHomo, despite its overall craniodental similarities toAustralopithecus africanus. The recently discovered South African speciesAustralopithecus sedibabrings further data to bear on this issue. As pointed out by Berger et al. [33], StW 53 appears to be more primitive than theAu. sedibaholotype MH1 in retaining closely spaced temporal lines; marked post- orbital constriction; a weakly developed supraorbital torus;

narrow, nonprojecting nasal bones; anterior pillars; marked nasoalveolar prognathism; medial and lateral expansion of the frontal process of the zygomatic bone; and laterally flared zygomatics. These features strongly call into question the assignment of StW 53 (and by extension O.H. 62) to the genusHomo.

Despite the previous emphasis on the presumed small size of the O.H. 62 specimen, there are numerous postcranial hominin fossils of relatively large body mass (likely > 49 kg) from East Africa that date to ca. 2.0 –1.8 Ma. These specimens include femora (KNM-ER 1472, KNM-ER 1481), and at least one os coxae (KNM ER 3228). While they almost certainly represent members of the genusHomo [34,35], due to the lack of associated crania they cannot be assigned with confidence at the species level, and could con- ceivably be representative of H. habilis,H. rudolfensis, or H. erectus/ergaster.

There have also been relatively recent discoveries of Homo erectus (sensu lato) whose estimated body sizes appear smaller than that originally posited for the KNM- WT 15000 specimen. In particular, specimens of early Homofrom the 1.8-million-year-old site of Dmanisi in the Republic of Georgia [36] appear to have been smaller than the 1993 “Nariokotome Boy’s” body mass estimate [37].

But the 1993 KNM-WT 15000 body size estimate itself has been called into question. Because the specimen had an erupted second molar, he was originally thought to have been about 11-12 years old at the time of his death, based on a modern human-like dental eruption schedule [38]. Research on enamel growth lines (the Striae of Retzius and their surface manifestations known as perikymata) preserved in teeth has called this view into question. Specifi- cally, the work of Christopher Dean, Gary Schwartz and others [39,40] suggests that the Turkana Boy was ca.

8 years old at the time of his death, which would indicate a different, faster, growth trajectory from that of a modern human. Therefore the question of how much growth was remaining for the Turkana Boy is a difficult one to answer, but recent work by Rhonda Graves and colleagues [41] indi- cates that at the time of his death the Turkana Boy had achieved more of his growth than would a modern human of a similar developmental age. The upshot of this research is that KNM-WT 15000 would in all likelihood not have grown to be ca. 185 cm tall, as was maintained by Ruff Table 2 Body mass, extant hominids (sensu lato). Data

from Fleagle [5] /La masse corporelle, Hominidés (sensu lato) actuels. Données de Fleagle [5].

Taxon Body mass (kg)

Pongo pygmaeusF 35.6

Pongo pygmaeusM 77.9

Pongo abelliF 35.8

Pongo abelliM 78.5

Pan troglodytes schweinfurthiiF 33.7 Pan troglodytes schweinfurthiiM 42.7 Pan troglodytes troglodytesF 45.8 Pan troglodytes troglodytesM 59.7

Pan troglodytes verusF 44.6

Pan troglodytes verusM 46.3

Pan paniscusF 33.2

Pan paniscusM 45

Gorilla gorilla gorillaF 71.5 Gorilla gorilla gorillaM 170.4

Gorilla gorilla diehliF 93

Gorilla gorilla diehliM 166

Gorilla beringei beringeiF 97.5 Gorilla beringei beringeiM 162.5 Gorilla beringei graueriF 71 Gorilla beringei graueriM 175.2

Homo sapiensF (low end) 42

Homo sapiensF (high end) 73

Homo sapiensM (low end) 47

Homo sapiensM (high end) 78

Fig. 1 Boxplot of body mass (kg), Miocene hominoids and extant hominids (sensu lato) /Boîte à moustaches de la taille corporelle (kg), hominoïdes du Miocène et hominidés (sensu lato) actuels.

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and Walker [37], but rather, would have much shorter (ca. 170 cm).

So what is the pattern of body size change betweenAus- tralopithecusandHomo? While many larger specimens of Australopithecusand smallerHomo erectusspecimens have been found in recent years, there still appears to be a significant difference in mean size between the two genera, with Homo[including specimens that may representH. habilisor H. rudolfensis) showing an increase in body size overAus- tralopithecus[32,35]. In particular, Holliday [32] noted that estimated body mass of earlyHomo(sensu lato) fell within modern human ranges of variation, while that ofAustralo- pithecusand“Paranthropus”(even including more recently discovered, larger specimens) when they fell within modern human ranges of variation, tended nonetheless to fall within the size range of modern human“Pygmies”(Fig. 3, repro- duced from [32] with permission from the publisher).

Body size evolution withinHomo

In 1997, Ruff and colleagues [42] looked at temporal changes in body mass within the genusHomoover the course of the last 1.8 million years. These workers took an ataxic approach, in that they did not divide the genus by species; allHomo, no matter what their specific assignments, were included in a single temporal analysis. This ataxic approach yielded some interesting results, but the primary interest of their research was to examine temporal changes in brain size relative to body size over the history of our genus, whereas the goal of the current paper is to examine evolutionary changes in body size itself. In this paper, Ruff’s data are augmented by data from the author in order to investigate these temporal trends in body mass. Differences between the approach taken by Ruff and colleagues and the current approach include the fact that here the European and Western Asian Neandertals are excluded from the analysis. While genetic data indicate

these hominins did contribute genes toH. sapiens, and that these genes are still observed in some populations of humans today [43], the amount of this genetic contribution is relatively low (ca. 1-4%), making the Neandertals somewhat tan- gential to the evolution of H. sapiens. A second difference between the 1997 paper and the current work is that in the current contribution the Holocene human sample is derived from the author’s database. The combined Pleistocene- Holocene sample is broken down into eight temporal units:

1.) an early Pleistocene sample (ca. 1.5-1.9 Ma); 2.) an early middle Pleistocene sample (ca. 400-600 ka); 3.) a later middle Pleistocene sample (ca. 200-300 ka); 4.) Skhul-Qafzeh anatomically modern, or nearly anatomically modern, hominins (ca. 90 ka); 5.) Early Upper Paleolithic modern humans (ca. 25-35 ka); 6.) Late Upper Paleolithic modern humans (ca.

10-20 ka); 7.) Early Historic Period (ca. 1-5 ka) recent humans; 8.) Twentieth Century humans. The latter two (Holo- cene) samples are divided by latitude, with low latitude (<30°

N or S latitude) groups coming from Africa, SE Asia, and Australia, while high latitude (>36° N latitude) groups are from Europe and North America (for a description of these samples, see [44]). Body mass was estimated from femoral head diameter as the arithmetic average of the results of two non-sex-specific least-squares regression formulae: 1.) that presented by Grine and colleagues [45] and 2.) that of Ruff et al. [42]. The formula from [45] has been shown to overes- timate body mass, while that of [42] tends to underestimate body mass [46]. Here, the average of the two estimates is used to reduce directional biases and provide a reliable body mass estimate.

Figure 4 shows mean body mass of the sample in relation to time before present. Note that following Ruff and colleagues’methodology, the temporal data are base 10 logarithmi- cally transformed. As argued by many workers [42,45,48]

the data show that body mass appears to increase from the earliest (early Pleistocene) members of the genusHomoto later, middle Pleistocene, members of the genus. It is in the Fig. 2 Estimated body mass (in kg) for a sample of Australopithecus afarensis individuals / La masse corporelle (kg ; estimée) pour un échantillon d’individus d’Australopithecus afarensis.Le spécimen « Lucy » est indiqué par la flèche.

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middle Pleistocene that hominins (variably referred to the speciesH. heidelbergensis) reach their heaviest mean mass, only to show a slight decrease in mass with the emergence of H. sapiensin the late Pleistocene [42,45]. There is also a subsequent, relatively steady, drop in body mass from the late Pleistocene through the mid-Holocene, which is fol- lowed by a very recent increase in body mass due to the global “secular trend” [42]. Note, however, that even the twentieth century, “secular trend” high latitude groups show a smaller mean body mass than the terminal Pleisto- cene (10-20 ka) sample.

What explanations have been offered for these temporal trends in the genusHomo? What could now be referred to as the traditional view is that the larger body size evident with the emergence ofH. erectuswas associated with increased ranging behavior associated with the need to exploit high- quality (read“high fat”) resources to feed the expanding and metabolically expensive brain in a nearly-runaway positive feedback loop [49, 50]. This was also tied to metabolic trade- offs in which the size of the gut was sacrificed in order to accommodate a larger brain (Aiello and Wheeler’s“Expen-

sive Tissue Hypothesis” [51]). It was also linked to older ideas about early hominins, including Glynn Isaac’s“home base”model regarding the foraging behavior of the makers of the Oldowan [52,53].

One problem with this traditional model, as recently pointed out by McCall [48], is that its timing appears to be off. As discussed above, while earlyHomodoes appear to be slightly larger in body size thanAustralopithecus/Paranthro- pus[32,35], the biggest increase in body size inHomocomes later than the Oldowan, or even the Acheulean, arising in the middle Pleistocene. What, then, could be conditioning this change? McCall [48] offers an interesting alternative hypothesis to the traditional view. He argues that the massive increase in body size from early to middle Pleistocene Homowas brought about by two main factors: 1.) they were living in relatively low population densities and 2.), they were relying on rich and reliable food resources. In McCall’s model, based on his analyses of data from African Early Stone Age (ESA) sites, the makers of the Oldowan and Acheulean were not using home bases as do hunter- gatherers in the ethnographic present, but rather were engaged Fig. 3 Estimated body mass (in kg) for multiple species of Australopithecus and Homo. Holocene H. sapiens are divided into three groups: high latitude (>36° N latitude); low latitude (<30° N or S); and“Pygmoid”people from Central Africa and Southeast Asia.

Taken from [32] with the permission of Chicago University Press /La masse corporelle (kg, estimée) pour des espèces d’Australopithe- cuset du genreHomo.L’échantillonH. sapiensHolocène est divisé en trois groupes : les régions froides (>36° N), les régions chaudes (<30° N ou S), et les populations « Pygmoïdes » d’Afrique centrale et d’Asie du sud-est. D’après [32] avec la permission de la Presse de l’Université de Chicago.

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in what has been referred to as“routed foraging”[54]–a form of resource extraction more typical of nonhuman primates than of modern humans. Such a system allows nonhuman primates to move efficiently through an environment with relatively evenly-dispersed resources, and since consumers move to the locations of resources they are not burdened with the cost of transporting resources back to a home base or other central location. McCall argues that the ESA foraging pattern was an augmented nonhuman primate pattern, but one with a higher level of carnivory, and hence larger home range size. Reliance on reliable, highly-ranked resources coupled with low population densities lifted energetic constraints on body size, allowing humans to become larger than at any other point in prehistory. In this regard, McCall’s model is similar to earlier ideas surrounding the evolutionary ecology of Oldowan hominins [49,51], it just moves the timing of this transition to a later date.

Where McCall’s model really departs from conventional thinking in prehistoric hominin evolutionary ecology is with his thoughts on the dynamics that led to the African Middle Stone Age (MSA) ca. 400,000 to 200,000 years ago. He

argues that with Homo having successfully filled a mixed predatory/scavenging niche in the early Pleistocene, by the middle Pleistocene hominin population size and density had grown to the point that humans were forced to exploit smaller home ranges. Because hominins are so efficient at resource extraction, primary, highly-ranked resources were becoming rarer on the landscape, and humans were therefore forced to exploit lower-quality and riskier resources at the same time their range sizes were contracting. This ultimately brought about the technological advances associated with the MSA, and corresponded with the first use of a“home base”foraging model. More importantly for the current discussion, however, this increase in population density and shift to riskier resources meant that energetic constraints on body size reap- peared, and humans again reduced in size–reductions that continued until a very recent shift (in wealthier nations, at least) during which high fat, high protein resources were once again readily available (the so-called“secular trend”).

The body mass data plotted in Figure 4 are very much in keeping with McCall’s model. One slight difference is that for the dataset used here, the major body size decrease in Fig. 4 Estimated body mass (in kg) for fossil and recentHomoplotted over the course of the Pleistocene and Holocene. The trend line passes through the mean of the high and low latitude recent humans, with the whiskers representing the low and high latitude means /La masse corporelle (kg, estimée) pour le genreHomo(fossile et récent) pendant le Pléistocène et l’Holocène. La ligne de tendance passe par la moyenne des groupes récents des régions froides et des régions tropicales, et les moustaches aux moyennes tropicales et froides.

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Homoseems to postdate the MSA, but as McCall notes, all of the late Pleistocene samples are nonetheless on average smaller in size than their presumed forebears in the middle Pleistocene.

Body mass differences among living Homo sapiens

As has been discussed above, body size in hominins has been investigated with regard to many factors, but perhaps none has been researched as frequently as has been its relationship to geography and climate. Specifically, body mass in humans and other widespread endothermic (warm-blooded) animal species is said to follow Bergmann’s (1847)“rule”. This ecogeographical rule posits that within a species or subspecies of geographically dispersed warm-blooded animals, those nearer the poles will tend to have higher body mass than do their conspecifics at lower latitudes. There is a considerable body of literature documenting morphological patterning in body size reflective of the operation of Bergmann’s rule among recent humans [44,55-61].

One traditional theoretical explanation for this pattern is that in order to conserve heat in colder regions, endothermic animals minimize the surface area: volume ratio (SA:V), since, according to Fourier’s Law of heat flow, heat loss is directly proportional to surface area (as well as to the difference between body core temperature and environmental temperature). Conversely, the loss of excess heat in hot environments may be facilitated by a relatively elevated SA:V ratio.

In this light, increasing body size (Bergmann’s rule) will tend to reduce this ratio, since body mass increase (which is volu- metric) is proportional to the third power of any linear size dimension increase, while the increase in surface area is only proportional to the square of the same linear dimension. This theoretical explanation is not accepted by all workers [62-64], but as Mayr [65] pointed out long ago, ecogeographical patterns are merely empirical observations whose validity is not dependent on what factor(s) cause(s) them. The fact that there is a significant negative relationship between temperature and body mass in humans, such that body mass among human populations decreases as mean annual temperature experi- enced by those groups increases [56,58,61], and the fact that similar patterns are observed in other endothermic species [64,65] adds credence to the notion that temperature is play- ing some role in conditioning body mass.

What some may find surprising is that the investigation of deviations from Bergmann’s rule is often more interesting than researching groups more closely adhering to its patterning. For example, one prominent group of outliers from the temperature/body size relationship is the Polynesians, who are much heavier than would be predicted from mean annual temperature alone. Linguistic and archeological evidence

have long suggested a recent Asian origin for this group [66,67), and Asians tend to show a more cold-adapted morphology for any given latitude than humans on other conti- nents; thus there may not have been enough time for selection to alter their body proportions.

The second notable outliers are the small-sized African and south Asian“Pygmy”groups who show a much smaller body mass than would be expected from latitude alone. In both Africa and Asia, these groups tend to live in tropical forests, and therefore humidity, rather than heat per se, may be the primary selective agent acting on body size and proportions [68-70]. In humid environments, sweating is much less effective in lowering body temperature. Since muscles operate at roughly 20% efficiency (the remaining 80% of liberated energy being released as heat), selection may favor individuals with reduced body mass (ca. 40% of which is skeletal muscle), since this lowers the total amount of body heat generated [70]. Other factors could also condi- tion “Pygmy” body size, such as reduced caloric requirements associated with smaller body mass [71] or the result of selection for early attainment of maturity in a high mortality environment [72; but see 73]. Poor nutrition and/or parasitic infections on their own, or in concert, do not, however, appear to be a sufficient explanation for“Pygmy”body size [74,77], and in fact, the reduction in“Pygmy”body size in Central Africa has recently been demonstrated to have a genetic basis, and to be under selection [75-77].

Despite the above caveat, the impact of nutrition on eco- geographic patterning in body size cannot be overlooked, since reduction in body size as the result of malnutrition is a well-documented phenomenon [78], and since, conversely, in situations in which there is high protein and fat intake, increased body size often results [79]. Indeed, the so-called

“secular trend”in human body size is seen as evidence of greater availability of dietary protein and fat. In an important paper, Katzmarzyk and Leonard [61] tested to see if there were global reductions in ecogeographical patterning due to the “secular trend”. They tested the idea that much of the cause for small body size in the tropics is due to the poverty and relatively poor nutrition characteristic of the people who live there. In order to test this hypothesis, they looked at the relationships between mean annual temperature and more recently collected anthropometric data (Many of Roberts’ and Newman’s data, so prominent in the literature, had been collected in the nineteenth century).

The anthropometric data Katzmarzyk and Leonard collected from the literature included body mass, BMI (body mass index), relative sitting height, and SA:V ratio. They discovered that while all relationships between morphology and temperature in their sample remained statistically significant, that the slopes for the relationship between most of the body size and shape variables and mean annual temperature were in fact shallower than those reported by Roberts [56,58].

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They attribute these shallower slopes to improving nutritional and health status among tropical groups.

Explanations for ecogeographical patterning in human body size other than adaptation to temperature abound in the literature, and include adaptation to humidity [69], reduction of energetic expenditures [80], selection for early sexual maturity in a high mortality environment [70], or even increased population density [48]. There is also the compli- cating issue of factors that are correlated with climate. For example, Endo and colleagues [81] argued that modern Japa- nese adhere to Bergmann’s Rule across the Japanese archipel- ago because in colder northern Japan people tend to consume more calories than do Japanese from warmer environs. Simi- larly, cold-adapted circumpolar foraging groups in the ethnographic present included a higher proportion of fat and protein in their diets for the simple reason that plant resources were largely unavailable in their environment [82,83].

Conclusions

Body mass is an important variable, and one which has shown much variation in human evolution. Hominids (sensu lato) are the largest of the primates and with the notable exception of the orangutan, among the most terrestrial. Despite a complex pattern, it appears that earlyHomo was in fact larger than Australopithecus. However, the largest hominins were those members of the genusHomowho lived near the end of the middle Pleistocene. Human body mass decreased throughout the late Pleistocene and into the Holocene, and has very recently increased due to the secular trend. Among humans today, there is evidence for ecogeographical patterning in body mass, and while climate is often implicated as a causal agent for differences in size across geography, there are other competing explanations for these differences.

Conflicts of interest :not any conflicts to declare.

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