Karen R. Rosenberg

Birth, obstetrics and human evolution.

There are several characteristics that set our species apart from other mammals. We are the only living or extant mammal that habitually walks on two legs. For our body size, we have the largest and the most complex brains of all animals. Humans depend on material culture or ‘tools’ for their survival. Humans universally communicate with each other through abstract symbols known as language. Finally, human females routinely seek assistance when they give birth. In fact, many have argued that midwifery or obstetrics, not prostitution, is the ‘oldest profession’. Fossil evidence shows that although two-legged walking, or bipedalism, traces its origin to the very beginning of human ancestry, tools and language appeared much more recently in human evolution. We will argue in this paper that, along with bipedalism, some aspects of the human pattern of birth trace their origin to the very beginning of human evolution. Based on fossil evidence from Africa, human paleontologists agree that the mammalian family to which humans belong, Hominidae (‘hominids’), originated approximately 5 million years ago. The crucial hallmarks of our earliest hominid ancestors are skeletal indicators of bipedalism. These markers appear clearly first in Australopithecus anamensis (ca. 4 million years ago) or possibly earlier. In spite of a human pattern of locomotion, these early members of the genus Australopithecus had brains that were smaller than modern humans—in proportion to their bodies—very similar to those of modern chimpanzees. Significant brain expansion did not begin until the origin of our genus, Homo, about 2.5 million years ago, when we also have evidence of the first stone tools. Evidence of language is not directly preserved in the fossil record but several investigators suggest that our ancestors were capable of the complex speech patterns that are part of all spoken languages today by at least 200,000 years ago. As noted above, we argue that assisted birth may be associated with bipedalism, and may thus be as old as the hominid family itself. However, assistance at birth is not the only significant birthrelated difference between humans and our close relatives in the primate order. The unusual way in which modern humans give birth is the result of a set of constraints imposed by bipedalism, a large brain, and ‘secondary altriciality’, or the delivery of the infant in a relatively helpless state. Birth in non-human primates

Why not the Neandertals

Some workers have suggested that a hypothetical genetic mutation in an African population less than 100,000 years ago led to a cascade of neurological changes in the human brain that culminated in the appearance of modern language. Language then triggered the socioeconomic and cognitive changes we associate with behavioral modernity and Africans, armed with behavioral modernity, then spread out from that continent, out-competing, displacing, extirpating, outbreeding or, most generally, replacing the Neandertals and other archaic humans throughout the middle latitudes of the Old World. The Neandertals of Europe are the best-known, best-represented and longest studied test case for this theory. In this paper we present evidence from skeletal anatomy, mitochondrial DNA, morphology and genetics of speech and the archaeology of the Middle-Upper Paleolithic transition in Europe that directly contradicts all of the elements in this replacement scenario. The processes leading to modernity involved the entire human species, and were based on the ethnogenic principle of communication and reticulation among populations.

Anatomy, Development, and Function of the Human Pelvis

The pelvis is an anatomically complex and functionally informative bone that contributes directly to both human locomotion and obstetrics. Because of the pelvis’ important role in obstetrics, it is one of the most sexually dimorphic bony elements of the human body. The complex intersection of pelvic dimorphism, locomotion, and obstetrics has been reenergized by exciting new research, and many papers in this special issue of the pelvis help provide clarity on the relationship between pelvic form (especially female) and locomotor function. Compared to the pelvis of our ape relatives, the human pelvis is uniquely shaped; it is superoinferiorly short and stout, and mediolaterally wide—critical adaptations for bipedalism that are already present in some form very early in the history of the hominin lineage. In this issue, 13 original research papers address the anatomy, development, variation, and function of the modern human pelvis, with implications for understanding the selection pressures that shaped and continue to shape this bone. This rich collection of scholarship moves our understanding of the pelvis forward, while raising dozens of new questions that we hope will serve as inspiration for colleagues and students (both current and future) puzzled by this fascinatingly complex bone. Anat Rec, 300:628–632, 2017.

Evolution of the Human Pelvis

No bone in the human postcranial skeleton differs more dramatically from its match in an ape skeleton than the pelvis. Humans have evolved a specialized pelvis, well‐adapted for the rigors of bipedal locomotion. Precisely how this happened has been the subject of great interest and contention in the paleoanthropological literature. In part, this is because of the fragility of the pelvis and its resulting rarity in the human fossil record. However, new discoveries from Miocene hominoids and Plio‐Pleistocene hominins have reenergized debates about human pelvic evolution and shed new light on the competing roles of bipedal locomotion and obstetrics in shaping pelvic anatomy. In this issue, 13 papers address the evolution of the human pelvis. Here, we summarize these new contributions to our understanding of pelvic evolution, and share our own thoughts on the progress the field has made, and the questions that still remain. Anat Rec, 300:789–797, 2017.

Neonatal Shoulder Width Suggests a Semirotational, Oblique Birth Mechanism in Australopithecus afarensis

Birth mechanics in early hominins are often reconstructed based on cephalopelvic proportions, with little attention paid to neonatal shoulders. Here, we find that neonatal biacromial breadth can be estimated from adult clavicular length (R2 = 0.80) in primates. Using this relationship and clavicular length from adult Australopithecus afarensis, we estimate biacromial breadth in neonatal australopiths. Combined with neonatal head dimensions, we reconstruct birth in A. afarensis (A.L. 288‐1 or Lucy) and find that the most likely mechanism of birth in this early hominin was a semi‐rotational oblique birth in which the head engaged and passed through the inlet transversely, but then rotated so that the head and shoulders remained perpendicular and progressed through the midplane and outlet oblique to the main axis of the female pelvis. Any other mechanism of birth, including asynclitic birth, would have resulted in either the head or the shoulders orthogonal to the short anteroposterior dimension of the A.L. 288‐1 pelvis, making birth untenable. There is a tight fit between the infant and all planes of the birth canal, perhaps suggesting a difficult labor in australopiths. However, the rotational birth mechanism of large‐brained humans today was likely not characteristic of A. afarensis. Thus, the evolution of rotational birth, usually associated with encephalization, may have occurred in two stages: the first appeared with the origin of the australopiths with their platypelloid pelves adapted for bipedalism and their broad‐shouldered neonates; the second which resulted in the modern mechanism of rotational birth may be associated with increasing brain size in the genus Homo. Anat Rec, 300:890–899, 2017.

On Neandertal Pubic Length

This response to Rosenberg 1988 reviews five key issues to assist in a clearer understanding of the drivers to Neandertal pelvic morphology. These are the relationship between maternal height/size and neonate size, neonate and maternal dimensions, selection on the pelvic aperture, what happens when this is too small, and sex determination from Neandertal remains.

Brother or Other: The Place of Neanderthals in Human Evolution

Few have provided insights and thoughtful explanations for Neanderthals that equal what have been a central theme in Yoel Rak’s publications. One of his deep understandings is that Neanderthals are another way of being human: not inferior, not superior, but different. Looking at what we now understand, Rak has been fundamentally correct in this insight, and where new discoveries have been unexpected, they serve to expand its scope and meaning. Unexpected new information about Neanderthal body form, demography, and even breeding behavior support and flesh out Rak’s essential insight about the place of Neanderthals in human evolution. In this paper some of the new discoveries and interpretations of Neanderthals and their evolution are discussed in this context. We examine three aspects of how Neanderthals are another way of being human: body shape (as revealed in the pelvis ), population structure (as revealed in their paleodemography), and breeding behavior (as revealed by paleogenetics, in the pattern of ancient gene flow). In these ways Neanderthals are like their ancestors, or more broadly are the plesiomorphic condition.