THE EVOLUTION OF EARLY HOMO: A REPLY TO SCOTT

Scott presents a welcome reply to our article, “A single lineage in early Pleistocene Homo” (Van Arsdale and Wolpoff 2012 ). However, Scott's reply mischaracterizes and fails to directly address the hypothesis of a single lineage that we test. Additionally, the approach taken by Scott fails to replicate the methods used in our analysis. As Scott himself suggests, our null hypothesis of a single evolving lineage in early Homo remains without refutation. Although many evolutionary scenarios might explain the complex pattern of variation present in the early Homo fossil record, the most parsimonious remains that of a single lineage displaying evolutionary change over time.     

Dental metric assessment of the omo fossils: implications for the phylogenetic position of Australopithecus africanus

The discovery of Australopithecus afarensis has led to new interpretations of hominid phylogeny, some of which reject A. africanus as an ancestor of Homo. Analysis of buccolingual tooth crown dimensions in australopithecines and Homo species by Johanson and White (Science 202:321-330, 1979) revealed that the South African gracile australopithecines are intermediate in size between Laetoli/hadar hominids and South African robust hominids. Homo, on the other hand, displays dimensions similar to those of A. afarensis and smaller than those of other australopithecines. These authors conclude, therefore, that A. africanus is derived in the direction of A. robustus and is not an ancestor of the Homo clade. However, there is a considerable time gap (ca. 800,000 years) between the Laetoli/Hadar specimens and the earliest Homo specimens; "gracile" hominids from Omo fit into this chronological gap and are from the same geographic area. Because the early specimens at Omo have been designated A. afarensis and the later specimens classified as Homo habilis, Omo offers a unique opportunity to test hypotheses concerning hominid evolution, especially regarding the phylogenetic status of A. africanus. Comparisons of mean cheek teeth breadths disclosed the significant (P less than or equal to 0.05) differences between the Omo sample and the Laetoli/Hadar fossils (P4, M2, and M3), the Homo fossils (P3, P4, M1, M2, and M1), and A. africanus (M3). Of the several possible interpretations of these data, it appears that the high degree of similarity between the Omo sample and the South African gracile australopithecine material warrants considering the two as geographical variants of A. africanus. The geographic, chronologic, and metric attributes of the Omo sample argue for its lineal affinity with A. afarensis and Homo. In conclusion, a consideration of hominid postcanine dental metrics provides no basis for removing A. africanus from the ancestry of the Homo lineage.     

Body weight prediction in early fossil hominids: Towards a taxon-“independent” approach

The choice of a model taxon is crucial when investigating fossil hominids that clearly do not resemble any extant species (such as Australopithecus) or show significant differences from modern human proportions (such as Homo habilis OH 62). An “interhominoid” combination is not adequate either, as scaling with body weight is strongly divergent in African apes and humans for most skeletal predictors investigated here. Therefore, in relation to a study of seven long bone dimensions, a new taxon-“independent” approach is suggested. For a given predictor, its taxonomic “independence” is restricted to the size range over which the body weight-predictor relationship for African apes and humans converges. Different predictors produce converging body weight estimates (BWEs) for different size ranges: taxon-“independent” estimates can be calculated for small- and medium-sized hominids (e. g., for weights below 50 kg) using femoral and tibial dimensions, whereas upper limb bones provide converging results for large hominids (above 50 kg). If the remains of Australopithecus afarensis really belong to one species, the relationship of male (above 60 kg) to female body weight (approximately 30 kg) does not fall within the observed range of modern hominoids. Considering Sts 14 (22 kg) to represent a small-sized Australopithecus africanus, the level of encephalization lies well above that of extant apes. If OH 62 (approximately 25 kg), with limb proportions less human-like than those of australopithecines, indeed represents Homo habilis (which has been questioned previously), an increase in relative brain size would have occurred well before full bipedality, an assumption running counter to current assumptions concerning early human evolution. © 1993 Wiley-Liss, Inc.     

对人类进化全过程的思索

本文从人类的诞生,人类发展过程的连续与间断,人类进化过程中体质发展的不平衡性和现代人的进化等４方面来论述人类进化的全过程．     

鄂西“南方古猿”和印尼早更新世若干人类化石

在鄂西发现的四枚臼齿化石曾被认为是南方古猿的。鄂西臼齿,从其齿冠尺寸和形状等来看,与非洲的有关材料对比,更接近人属成员的;与印尼早更新世有关的化石对比,与魁人等的很相似。直立人牙齿的演化趋势和变异性表明:鄂西臼齿以及印尼早更新世人类下颌骨化石更大的可能是代表一类时代较早的直立人。     

鄂西“南方古猿”和印尼早更新世若干人类化石

在鄂西发现的四枚臼齿化石曾被认为是南方古猿的。鄂西臼齿,从其齿冠尺寸和形状等来看,与非洲的有关材料对比,更接近人属成员的;与印尼早更新世有关的化石对比,与魁人等的很相似。直立人牙齿的演化趋势和变异性表明:鄂西臼齿以及印尼早更新世人类下颌骨化石更大的可能是代表一类时代较早的直立人。     

Femoral lengths and stature in Plio-Pleistocene hominids

This study reports the femoral lengths of 31 Plio-Pleistocene hominids dated between 3.1 and 0.7 million years ago, and uses those lengths to estimate stature by way of the femur-stature ratio reported by Feldesman et al. (Am. J. Phys. Anthropol. 78:219-220, 1989). By this method the average female Australopithecus afarensis is 105 cm and the average male is 151 cm. The respective values are 115 and 138 cm for A. africanus. As defined by Howell (In VJ Maglio and HBS Cooke (eds): The Evolution of African Mammals. Cambridge: Harvard University Press, 1978) and Johanson et al. (Kirtlandia 28:1-14, 1978), Homo habilis is a sexually dimorphic species, with females standing 118 cm and males 157 cm. Such apparently strong dimorphism may be due to the possibility that there are actually two species of nonrobust hominids between 2 and 1.7 m.y.a. The estimate for the female Australopithecus boisei is 124 cm and for the male, 137 cm, but these estimates are especially difficult to be certain of because there are no femora that can be positively identified as male A. boisei. Australopithecus robustus is estimated to be 110 cm (female) and 132 cm (male). African Homo erectus stood 160 cm (female) and 180 cm (male). From these estimates several generalizations are apparent. First, there is apparently strong sexual dimorphism in stature in A. afarensis and H. habilis, but less in the other species. Second, the "robust" australopithecines were relatively small statured. Third, it is apparently not true that humans have been getting progressively taller throughout their evolutionary history. Some individuals were as tall as modern humans 3 m.y.a., by 2 m.y.a. one individual stood about 173 cm, and by 1.7 m.y.a. a stature of 180+ cm was not uncommon.     

Climatic adaptation and hominid evolution: The thermoregulatory imperative

Anthropologists have long recognized the existence among modern humans of geographical variations in body form that parallel climatic gradients, part of more general zoological phenomena commonly referred to as Bergmann's or Allen's “Rules”. These observations have rarely been applied to earlier hominids, in part because fossil skeletons usually are so incomplete that it is difficult to reconstruct body morphology accurately. However, within the past two decades two early hominids have been discovered that preserve enough of the skeleton to allow confident assessment of their body size and shape. Comparison of these specimens—the Australopithecus afarensis A.L. 288-1 (“Lucy”) and the Homo erectus KNM-WT 15000—with others that are less complete make it evident that the evolution of Homo erectus was accompanied by not only a marked increase in body size, but also a similarly dramatic increase in the linearity of body form. That is, relative to their heights, small australopithecines had very broad bodies, whereas large early Homo had narrow bodies. This difference in body form cannot be explained on the basis of obstetric or biomechanical factors, but is consistent with thermoregulatory constraints on body shape. Specifically, to maintain the same ratio of body surface area to body mass, which is an important thermoregulatory mechanism, increases in height should be accompanied by no change in body breadth, which is exactly what is seen in comparisons of A.L. 288-1 and KNM-WT 15000. Conversely, Neandertals living in colder climates had much wider bodies, which are adaptive for heat retention. Differences in limb length proportions between fossil hominids are also consistent with thermoregulatory principles and the geographic variation observed among modern humans. Climatic adaptation during hominid evolution may have wide-ranging implications, not only with regard to interpreting body morphology, but also in relation to ecological scenarios, population movements, and the evolution of the brain.     

Was “Lucy” more human than her “child”? Observations on early hominid postcranial skeletons

Fully adult partial skeletons attributed to Australopithecus afarensis (AL 288-1, “Lucy”) and to Homo habilis (OH 62, “Lucy's child”), respectively, both include remains from upper and lower limbs. Relationships between various limb bone dimensions of these skeletons are compared to those of modern African apes and humans. Surprisingly, it emerges that OH 62 displays closer similarities to African apes than does AL 288-1. Yet A. afarensis, whose skeleton is dated more than 1 million years earlier, is commonly supposed to be the ancestor of Homo habilis. If OH 62, classified as Homo habilis by its discoverers, does indeed represent a stage intermediate between A. afarensis and later Homo, a revised interpretation of the course of human evolution would be necessary.     

The australopithecines in review

Over the past 75 years since the discovery of the first australopithecine at Taung in southern Africa there has been a growing realisation that there is no simple, linear ancestor-descendant relationship connecting the australopithecines to laterHomo. There are currently at least ten recognised species of australopithecine, including two species of earlyHomo, that have been recently transferred to the genusAustralopithecus. These known species span the period between about 4.2-1.2 Ma and throughout the majority of this period there are multiple contemporaneous hominin species in eastern and southern Africa. This contribution reviews current knowledge about the australopithecine species and their inferred relationships to each other and to the genusHomo. At present it is impossible to resolve the phylogenetic relationships of the australopithecines with any degree of confidence. There is a growing realisation of the ‘bushy’ nature of hominin evolution throughout the australopithecine period and also of the inevitability that additional early hominin species remain to be discovered. Paper submitted for inclusion in the Proceedings of the International Symposium of the Ramón Areces Foundation “Evolution of the Human Family: State of the Art” held in Madrid on the 11–13 March, 1998     

Homo erectus—who,when and where: A survey

The state of information bearing on Homo erectus as developed since about 1960 is surveyed, with the resulting effects on problems. Definitions of H. erectus still rest on the Far Eastern samples (Chou-k'ou-tien/Java), and thus relate to late Lower to middle Middle Pleistocene material. Numerous important individual finds, however, have expanded the total: extension of the early and very early Sangiran material; very early to later in Africa, and relatively late in Europe. Datings remain uncertain or controversial within broad limits, but with some important successes and revisions. Discussion by authors of problems concerns degree of divergence among H. erectus populations and rate of evolutionary change; both appear relatively slight, but the data are inadequate for much present judgment. The apparent zone of transition to more advanced morphology (H. sapiens, sensu lato) by the late Middle Pleistocene better reflects signs of regional divergence. Some writers—not all—believe that even the earliest European fossils known (e.g., Petralona) had already advanced to a H. sapiens basic level, with later change in the direction of Neanderthals. A separate African phylum, from OH 9, is also suggested; recent Chinese finds may provide a third different post-erectus population before the Upper Pleistocene. Taxonomic expression of all this gives some problems.     

安徽和县猿人化石的初步研究

本文主要记述了1980年在安徽和县龙潭洞发现的一个猿人头骨化石。它是一个男性青年的脑颅,具有直立人的许多典型性状,分类上当属直立人(Homo erectus)。初步研究表明,它在形态上和北京猿人较为相似,但又具有若干较北京猿人为进步的性状。因此,该头骨代表了一种进步类型的直立人。根据目前的认识,它的系统位置似应与较晚的北京猿人相当。     

How big were early hominids?

The recent discovery of new postcranial fossils, particularly associated body parts, of several Plio-Pleistocene hominids provides a new opportunity to assess body size in human evolution.¹ Body size plays a central role in the biology of animals because of its relationship to brain size, feeding behavior, habitat preference, social behavior, and much more. Unfortunately, the prediction of body weight from fossils is inherently inaccurate because skeletal size does not reflect body size exactly and because the fossils are from species having body proportions for which there are no analogues among modern species. The approach here is to find the relationship between body size and skeletal size in ape and human specimens of known body weight at death and to apply this knowledge to the hominid fossils, using a variety of statistical methods, knowledge of the associated partial skeletons of the of early hominids, formulae derived from a modern human sample, and, finally, common sense. The following modal weights for males and females emerge: Australopithecus afarensis, 45 and 29 kg; A. africanus, 41 and 30 kg; A. robustus, 40 and 32 kg; A. boisei, 49 and 34 kg; H. habilis, 52 and 32 kg. The best known African early H. erectus were much larger with weights ranging from 55 kg on up. These estimates imply that (1) in the earliest hominid species and the “robust” australopithecines body sizes remained small relative to modern standards, but between 2.0 and 1.7 m.y.a. there was a rapid increase to essentially modern body size with the appearance of Homo erectus; (2) the earliest species had a degree of body size sexual dimorphism well above that seen in modern humans but below that seen in modern gorillas and orangs which implies (along with other evidence) a social organization characterized by kin-related, multi-male groups with females who were not kin-related; (3) relative brain sizes increased through time; (4) there were two divergent trends in relative cheek-tooth size—a steady increase through time from A. afarensis to A. africanus to the “robust” australopithecines, and a decrease beginning with H. habilis to H. erectus to H. sapiens.