A computational survey of the human genome has identified more than 500 human-specific genomic deletions that remove sequences that are highly conserved between chimpanzees and other animals. These are genomic changes that are likely to have contributed to unique features of human biology. Most of the deleted sequences are located in the non-coding regions of the genome. The human deletions are enriched near genes involved in neural development and steroid hormone signalling, consistent with previous suggestions that regulatory changes near key developmental control genes may have important roles in human evolution. Specific examples of human-specific deletions include one that affects penile anatomy and another relating to brain size. This study searched for putative regulatory mutations specific to the human lineage by looking for sequences that are highly conserved between chimpanzees and other species, but are not present in the human genome. The 500-odd human-specific deletions tend to lie in non-coding DNA stretches and near genes involved in steroid hormone signalling and neural function. This is illustrated with two examples, one of which affects penile anatomy whereas the other affects brain size. Humans differ from other animals in many aspects of anatomy, physiology, and behaviour; however, the genotypic basis of most human-specific traits remains unknown1. Recent whole-genome comparisons have made it possible to identify genes with elevated rates of amino acid change or divergent expression in humans, and non-coding sequences with accelerated base pair changes2,3,4,5. Regulatory alterations may be particularly likely to produce phenotypic effects while preserving viability, and are known to underlie interesting evolutionary differences in other species6,7,8. Here we identify molecular events particularly likely to produce significant regulatory changes in humans: complete deletion of sequences otherwise highly conserved between chimpanzees and other mammals. We confirm 510 such deletions in humans, which fall almost exclusively in non-coding regions and are enriched near genes involved in steroid hormone signalling and neural function. One deletion removes a sensory vibrissae and penile spine enhancer from the human androgen receptor (AR) gene, a molecular change correlated with anatomical loss of androgen-dependent sensory vibrissae and penile spines in the human lineage9,10. Another deletion removes a forebrain subventricular zone enhancer near the tumour suppressor gene growth arrest and DNA-damage-inducible, gamma (GADD45G)11,12, a loss correlated with expansion of specific brain regions in humans. Deletions of tissue-specific enhancers may thus accompany both loss and gain traits in the human lineage, and provide specific examples of the kinds of regulatory alterations6,7,8 and inactivation events13 long proposed to have an important role in human evolutionary divergence.

The substantial fossil record for Australopithecus afarensis includes both an adult partial skeleton [Afar Locality (A.L.) 288-1, “Lucy”] and a large simultaneous death assemblage (A.L. 333). Here we optimize data derived from both to more accurately estimate skeletal size dimorphism. Postcranial ratios derived from A.L. 288-1 enable a significant increase in sample size compared with previous studies. Extensive simulations using modern humans, chimpanzees, and gorillas confirm that this technique is accurate and that skeletal size dimorphism in A. afarensis was most similar to that of contemporary Homo sapiens . These data eliminate some apparent discrepancies between the canine and skeletal size dimorphism in hominoids, imply that the species was not characterized by substantial sexual bimaturation, and greatly increase the probability that the reproductive strategy of A. afarensis was principally monogamy.

▪ Abstract Our understanding of developmental biology burgeoned during the last decade. This review summarizes recent advances, provides definitions and explanations of some basic principles, and does so in a way that will aid anthropologists in understanding their profound implications. Crucial concepts, such as developmental fields, selector and realizator genes, cell signaling mechanisms, and gene regulatory elements are briefly described and then integrated with the emergence of skeletal morphology. For the postcranium, a summary of events from limb bud formation, the appearance of anlagen, the expression of Hox genes, and the fundamentals of growth plate dynamics are briefly summarized. Of particular importance are revelations that bony morphology is largely determined by pattern formation, that growth foci such as physes and synovial joints appear to be regulated principally by positional information, and that variation in these fields is most likely determined by cis-regulatory elements acting on restricted numbers of anabolic genes downstream of selectors (such as Hox). The implications of these discoveries for the interpretation of both contemporary and ancient human skeletal morphology are profound. One of the most salient is that strain transduction now appears to play a much reduced role in shaping the human skeleton. Indeed, the entirety of “Wolff's Law” must now be reassessed in light of new knowledge about pattern formation. The review concludes with a brief discussion of some implications of these findings, including their impact on cladistics and homology, as well as on biomechanical and morphometric analyses of both ancient and modern human skeletal material.

In a previous study, we introduced the template method as a means of enlarging the Australopithecus afarensis postcranial sample to more accurately estimate its skeletal dimorphism. Results indicated dimorphism to be largely comparable to that of Homo sapiens . Some have since argued that our results were biased by artificial homogeneity in our Au. afarensis sample. Here we report the results from inclusion of 12 additional, newly reported, specimens. The results are consistent with those of our original study and with the hypothesis that early hominid demographic success derived from a reproductive strategy involving male provisioning of pair-bonded females.