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<jats:p> The highly fragmented and distorted skull of the adult skeleton <jats:italic>ARA-VP-6/500</jats:italic> includes most of the dentition and preserves substantial parts of the face, vault, and base. Anatomical comparisons and micro–computed tomography–based analysis of this and other remains reveal pre- <jats:italic>Australopithecus</jats:italic> hominid craniofacial morphology and structure. The <jats:italic>Ardipithecus ramidus</jats:italic> skull exhibits a small endocranial capacity (300 to 350 cubic centimeters), small cranial size relative to body size, considerable midfacial projection, and a lack of modern African ape–like extreme lower facial prognathism. Its short posterior cranial base differs from that of both <jats:italic>Pan troglodytes</jats:italic> and <jats:italic>P. paniscus</jats:italic> . <jats:italic>Ar. ramidus</jats:italic> lacks the broad, anteriorly situated zygomaxillary facial skeleton developed in later <jats:italic>Australopithecus</jats:italic> . This combination of features is apparently shared by <jats:italic>Sahelanthropus</jats:italic> , showing that the Mio-Pliocene hominid cranium differed substantially from those of both extant apes and <jats:italic>Australopithecus</jats:italic> . </jats:p>

<jats:p> The Middle Awash <jats:italic>Ardipithecus ramidus</jats:italic> sample comprises over 145 teeth, including associated maxillary and mandibular sets. These help reveal the earliest stages of human evolution. <jats:italic>Ar. ramidus</jats:italic> lacks the postcanine megadontia of <jats:italic>Australopithecus</jats:italic> . Its molars have thinner enamel and are functionally less durable than those of <jats:italic>Australopithecus</jats:italic> but lack the derived <jats:italic>Pan</jats:italic> pattern of thin occlusal enamel associated with ripe-fruit frugivory. The <jats:italic>Ar. ramidus</jats:italic> dental morphology and wear pattern are consistent with a partially terrestrial, omnivorous/frugivorous niche. Analyses show that the <jats:italic>ARA-VP-6/500</jats:italic> skeleton is female and that <jats:italic>Ar. ramidus</jats:italic> was nearly monomorphic in canine size and shape. The canine/lower third premolar complex indicates a reduction of canine size and honing capacity early in hominid evolution, possibly driven by selection targeted on the male upper canine. </jats:p>

<jats:p> The <jats:italic>Ardipithecus ramidus</jats:italic> hand and wrist exhibit none of the derived mechanisms that restrict motion in extant great apes and are reminiscent of those of Miocene apes, such as <jats:italic>Proconsul</jats:italic> . The capitate head is more palmar than in all other known hominoids, permitting extreme midcarpal dorsiflexion. <jats:italic>Ar. ramidus</jats:italic> and all later hominids lack the carpometacarpal articular and ligamentous specializations of extant apes. Manual proportions are unlike those of any extant ape. Metacarpals 2 through 5 are relatively short, lacking any morphological traits associable with knuckle-walking. Humeral and ulnar characters are primitive and like those of later hominids. The <jats:italic>Ar. ramidus</jats:italic> forelimb complex implies palmigrady during bridging and careful climbing and exhibits none of the adaptations to vertical climbing, forelimb suspension, and knuckle-walking that are seen in extant African apes. </jats:p>

<jats:p> The femur and pelvis of <jats:italic>Ardipithecus ramidus</jats:italic> have characters indicative of both upright bipedal walking and movement in trees. Consequently, bipedality in <jats:italic>Ar. ramidus</jats:italic> was more primitive than in later <jats:italic>Australopithecus</jats:italic> . Compared with monkeys and Early Miocene apes such as <jats:italic>Proconsul</jats:italic> , the ilium in <jats:italic>Ar. ramidus</jats:italic> is mediolaterally expanded, and its sacroiliac joint is located more posteriorly. These changes are shared with some Middle and Late Miocene apes as well as with African apes and later hominids. However, in contrast to extant apes, bipedality in <jats:italic>Ar. ramidus</jats:italic> was facilitated by craniocaudal shortening of the ilium and enhanced lordotic recurvature of the lower spine. Given the predominant absence of derived traits in other skeletal regions of <jats:italic>Ar. ramidus</jats:italic> , including the forelimb, these adaptations were probably acquired shortly after divergence from our last common ancestor with chimpanzees. They therefore bear little or no functional relationship to the highly derived suspension, vertical climbing, knuckle-walking, and facultative bipedality of extant African apes. </jats:p>

<jats:p> Several elements of the <jats:italic>Ardipithecus ramidus</jats:italic> foot are preserved, primarily in the <jats:italic>ARA-VP-6/500</jats:italic> partial skeleton. The foot has a widely abducent hallux, which was not propulsive during terrestrial bipedality. However, it lacks the highly derived tarsometatarsal laxity and inversion in extant African apes that provide maximum conformity to substrates during vertical climbing. Instead, it exhibits primitive characters that maintain plantar rigidity from foot-flat through toe-off, reminiscent of some Miocene apes and Old World monkeys. Moreover, the action of the fibularis longus muscle was more like its homolog in Old World monkeys than in African apes. Phalangeal lengths were most similar to those of <jats:italic>Gorilla</jats:italic> . The <jats:italic>Ardipithecus</jats:italic> gait pattern would thus have been unique among known primates. The last common ancestor of hominids and chimpanzees was therefore a careful climber that retained adaptations to above-branch plantigrady. </jats:p>

<jats:p> Genomic comparisons have established the chimpanzee and bonobo as our closest living relatives. However, the intricacies of gene regulation and expression caution against the use of these extant apes in deducing the anatomical structure of the last common ancestor that we shared with them. Evidence for this structure must therefore be sought from the fossil record. Until now, that record has provided few relevant data because available fossils were too recent or too incomplete. Evidence from <jats:italic>Ardipithecus ramidus</jats:italic> now suggests that the last common ancestor lacked the hand, foot, pelvic, vertebral, and limb structures and proportions specialized for suspension, vertical climbing, and knuckle-walking among extant African apes. If this hypothesis is correct, each extant African ape genus must have independently acquired these specializations from more generalized ancestors who still practiced careful arboreal climbing and bridging. African apes and hominids acquired advanced orthogrady in parallel. Hominoid spinal invagination is an embryogenetic mechanism that reoriented the shoulder girdle more laterally. It was unaccompanied by substantial lumbar spine abbreviation, an adaptation restricted to vertical climbing and/or suspension. The specialized locomotor anatomies and behaviors of chimpanzees and gorillas therefore constitute poor models for the origin and evolution of human bipedality. </jats:p>

<jats:p> Referential models based on extant African apes have dominated reconstructions of early human evolution since Darwin’s time. These models visualize fundamental human behaviors as intensifications of behaviors observed in living chimpanzees and/or gorillas (for instance, upright feeding, male dominance displays, tool use, culture, hunting, and warfare). <jats:italic>Ardipithecus</jats:italic> essentially falsifies such models, because extant apes are highly derived relative to our last common ancestors. Moreover, uniquely derived hominid characters, especially those of locomotion and canine reduction, appear to have emerged shortly after the hominid/chimpanzee divergence. Hence, <jats:italic>Ardipithecus</jats:italic> provides a new window through which to view our clade’s earliest evolution and its ecological context. Early hominids and extant apes are remarkably divergent in many cardinal characters. We can no longer rely on homologies with African apes for accounts of our origins and must turn instead to general evolutionary theory. A proposed adaptive suite for the emergence of <jats:italic>Ardipithecus</jats:italic> from the last common ancestor that we shared with chimpanzees accounts for these principal ape/human differences, as well as the marked demographic success and cognitive efflorescence of later Plio-Pleistocene hominids. </jats:p>

<jats:title>Ultimate Simulator</jats:title> <jats:p> Many body problems are difficult to model analytically and are often so complex that they cannot be simulated accurately on a classical computer. Because quantum systems can be inherently correlated, it has been proposed that such systems could be used to simulate other complex problems. <jats:bold>Buluta and Nori</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="108" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1177838">108</jats:related-article> ) review the progress being made toward realizing quantum simulators, describing some of the implementations and potential applications of using such controlled quantum systems as simulator tools. </jats:p>

<jats:p>Long-period surface waves from oceanic or atmospheric disturbances can be used for seismic mapping of the upper mantle.</jats:p>

<jats:title>Quiet, Please</jats:title> <jats:p> One approach for building quantum computers is based on superconductors with appropriately designed components to control the pairs of charges flowing through the circuits. However, at the single-electron level, required quantum noise—generated by quantum fluctuations and throwing offset charges into the device—presents a real problem in manipulating the delicate quantum states of the qubits. <jats:bold> Manucharyan <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="113" related-article-type="in-this-issue" vol="326" xlink:href="10.1126/science.1175552">113</jats:related-article> ) present a clever piece of quantum circuit engineering that can suppress the effect of the quantum noise and allow the quantum circuit to operate without disturbance. </jats:p>