Scientific Understanding of Consciousness
Evolution of the Brain Recent Research
Science 2 October 2009: Vol. 326. no. 5949, pp. 68
The Ardipithecus ramidus Skull and Its Implications for Hominid Origins
Gen Suwa,1 Berhane Asfaw,2 Reiko T. Kono,3 Daisuke Kubo,4 C. Owen Lovejoy,5 Tim D. White6
1 The University Museum, the University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
The first fossil of Australopithecus, a partial child’s skull found in 1924 at Taung, South Africa, was reported by R. A. Dart to combine an ape-like cranial capacity with distinctive hominid features such as weak facial prognathism, small anterior deciduous teeth, and an anteriorly situated foramen magnum. Since then, diverse Plio-Pleistocene cranial fossils have been recovered, primarily in southern and eastern Africa, establishing a widely recognized Australopithecus grade of evolution. Australopithecus crania exhibit small, chimpanzee-to-gorilla–sized cranial capacities, distinct cranial base flexion, and varying degrees of postcanine megadonty with associated craniofacial/vault morphologies. The derivation of the genus Homo from Pliocene Australopithecus is probable, whereas the pre-Pliocene ancestry of Australopithecus has been elusive.
Until now, the only substantial specimen to shed any light on pre-Australopithecus hominid cranial evolution was that of Sahelanthropus tchadensis from Chad. Discovered in 2001, this Late Miocene cranium [specimen TM 266-01-060-1; estimated at 6.0 to 7.0 million years ago (Ma)] combines a cranial capacity smaller than Australopithecus with a long and low neurocranium, an anteriorly extended upper face surmounted by a massive supraorbital torus with no post-toral sulcus, and a lower face less prognathic than those of either chimpanzees or gorillas. The posterior vault and cranial base are described as resembling post–3.5 Ma Pliocene Australopithecus. However, the hominid status of S. tchadensis has been challenged; some opined that it exhibits a surprisingly evolved face, whereas others have suggested it to be a gorilla ancestor or some other ape.
We report here the skull of Ardipithecus ramidus recovered from Aramis, Ethiopia, as a part of the ARA-VP-6/500 skeleton. Together with other key Aramis specimens, including the ARA-VP-1/500 temporal/occipital portion, these fossils constitute the first substantial cranial remains of a pre-Australopithecus hominid directly associated with extensive postcranial remains. The Ar. ramidus postcranium indicates both substantial arboreal capability and an intermediate form of terrestrial bipedality that preceded the more fully established Australopithecus condition. The revelation of a primitive pre-Austalopithecus locomotor grade raises substantial interest in establishing the major features of the Ardipithecus cranium. Did Ar. ramidus share any of the derived hominid features seen in Australopithecus, or did it exhibit a skull more like those of extant African apes? What are its implications with respect to the controversies surrounding the hominid status of Sahelanthropus? We seek answers to these questions by comparing the Aramis fossils to Australopithecus, Sahelanthropus, and extant African apes, and we offer new hypotheses about cranial evolution in the hominid and African ape clades.
The highly fragmented and distorted skull of the adult skeleton ARA-VP-6/500 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-Australopithecus hominid craniofacial morphology and structure. The Ardipithecus ramidus 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 Pan troglodytes and P. paniscus. Ar. ramidus lacks the broad, anteriorly situated zygomaxillary facial skeleton developed in later Australopithecus. This combination of features is apparently shared by Sahelanthropus, showing that the Mio-Pliocene hominid cranium differed substantially from those of both extant apes and Australopithecus.
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Nature 460, 190-196 (9 July 2009)
Marc D. Hauser
Departments of Psychology, Human Evolutionary Biology, and Organismic & Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Human Cultural Revolution
Although anthropologists disagree about the timing of the human cultural revolution, many researchers point to fundamental changes starting some 800,000 years ago in the Early Palaeolithic, with a crescendo of change at around 45,000–40,000 years ago in the Late Palaeolithic. This period is associated with the generation of symbols (mathematical, artistic and ritualistic), controlled fire for use in cooking and other forms of environmental transformation, and tools with multiple components and functions (for example, tools used for expressing both aggression and music). Given that this interval of several thousand years is barely noticeable on an evolutionary timescale, and that such cultural expressions emerged rapidly, the parallel with the Cambrian is striking: that is, something similar to a genetic revolution must have occurred during this period, providing humans with an unprecedented set of capacities for generating novel cultural expressions in language, morality, music and technology. Specifically, at some point before or during the Paleolithic, the human brain was transformed from a system with a high degree of modularity with few interfaces to a system of modules with numerous promiscuous and combinatorially creative interfaces.
Science 5 June 2009: Vol. 324. no. 5932, pp. 1298 - 1301
Late Pleistocene Demography and the Appearance of Modern Human Behavior
Adam Powell,1,3 Stephen Shennan,2,3 Mark G. Thomas1,3,
1 Research Department of Genetics, Evolution, and Environment, University College London, Wolfson House, 4 Stephenson Way, London NW1 2HE, UK.
The origins of modern human behavior are marked by increased symbolic and technological complexity in the archaeological record. In western Eurasia this transition, the Upper Paleolithic, occurred about 45,000 years ago, but many of its features appear transiently in southern Africa about 45,000 years earlier. We show that demography is a major determinant in the maintenance of cultural complexity and that variation in regional subpopulation density and/or migratory activity results in spatial structuring of cultural skill accumulation. Genetic estimates of regional population size over time show that densities in early Upper Paleolithic Europe were similar to those in sub-Saharan Africa when modern behavior first appeared. Demographic factors can thus explain geographic variation in the timing of the first appearance of modern behavior without invoking increased cognitive capacity.
The Upper Paleolithic (UP) transition, which occurred in Europe and western Asia about 45 thousand years ago (ka), and later in southern and eastern Asia, Australia, and Africa, is seen by many as marking the origins of modern human behavior. UP material culture, usually referred to as the Late Stone Age (LSA) in Africa, is characterized by a substantial increase in technological and cultural complexity, including the first consistent presence of symbolic behavior, such as abstract and realistic art and body decoration (e.g., threaded shell beads, teeth, ivory, ostrich egg shells, ochre, and tattoo kits); systematically produced microlithic stone tools (especially blades and burins); functional and ritual bone, antler, and ivory artifacts; grinding and pounding stone tools; improved hunting and trapping technology (e.g., spear throwers, bows, boomerangs, and nets); an increase in the long-distance transfer of raw materials; and musical instruments, in the form of bone pipes.
In Europe and western Asia, the UP transition happened relatively rapidly, with most of the characteristic features listed above appearing (the "full package"), and is thought to coincide with the appearance of anatomically modern humans (AMH) in a region previously occupied by Neanderthals. In southern Siberia and northeast Asia, microlithic technology appears between 43 and 27 ka, but a fuller UP package is not evident until ~22 ka. The evidence from south and southeast Asia and Australia also points to a more gradual accumulation of modern behavioral traits (ornamentation, use of ochre, and possibly rock art). These are thought to first appear soon after the initial expansions of AMH into the regions but only become widespread later on, ~30 ka and ~20 ka, if not later, in south Asia and Australia, respectively. In Africa, the idea of a single transition has been contested because there is strong evidence for the sporadic appearance of many markers of modern behavior at multiple sites as early as 70 to 90 ka, and possibly as far back as 160 ka. The African Middle Stone Age (MSA) sites of Katanda, Democratic Republic of Congo (~90 ka); Klasies River mouth (Howieson’s Poort and Still Bay industries), South Africa (~65 to 70 ka) ; and, in particular, Blombos Cave, South Africa (~75 ka) present a striking array of modern traits, including the earliest evidence of abstract art, as well as geometric blades, barbed bone harpoon points, bone awls, and marine shell personal ornaments. However, these markers are intermittent and disappear between ~75 and 60 ka before making a more stable and widespread reappearance in the LSA starting ~40 ka.
Science 7 September 2007: Vol. 317. no. 5843, pp. 1402 - 1405
Justin N. Wood,1 David D. Glynn,1 Brenda C. Phillips,4 Marc D. Hauser1,2,3
1 Department of Psychology, Harvard University, Cambridge, MA 02138, USA.
Humans are capable of making inferences about other individuals' intentions and goals by evaluating their actions in relation to the constraints imposed by the environment. This capacity enables humans to go beyond the surface appearance of behavior to draw inferences about an individual's mental states. Presently unclear is whether this capacity is uniquely human or is shared with other animals. We show that cotton-top tamarins, rhesus macaques, and chimpanzees all make spontaneous inferences about a human experimenter's goal by attending to the environmental constraints that guide rational action. These findings rule out simple associative accounts of action perception and show that our capacity to infer rational, goal-directed action likely arose at least as far back as the New World monkeys, some 40 million years ago.
A central characteristic of human action perception is the capacity to read beneath the surface appearance of behavior. When someone acts, we make inferences about their goals and intentions by referencing each action against a backdrop of environmental constraints. In humans, this capacity appears around the first year of life.
Nature, Vol 443, 14 September 2006, p.167
An RNA gene expressed during cortical development evolved rapidly in humans
Brains of humans and chimpanzees are anatomically not so different, except in scale. About two million years ago, the hominin brain began to enlarge until, in modern times, it has become about three times larger than that of the chimpanzees. A study revealed 49 regions, each with a sequence that is highly evolutionarily conserved among many mammals, but has diverged rapidly in humans since our last common ancestor with chimpanzees. One RNA gene, in particular, has a crucial role in redirecting migrating neurons and is a strong candidate for a determinant of innovative function in the human neocortex.
The developmental and evolutionary mechanisms behind the emergence of human-specific brain features remain largely unknown. However, the recent ability to compare our genome to that of our closest relative, the chimpanzee, provides new avenues to link genetic and phenotypic changes in the evolution of the human brain. We devised a ranking of regions in the human genome that show significant evolutionary acceleration. Here we report that the most dramatic of these 'human accelerated regions', HAR1, is part of a novel RNA gene (HAR1F) that is expressed specifically in Cajal–Retzius neurons in the developing human neocortex from 7 to 19 gestational weeks, a crucial period for cortical neuron specification and migration. HAR1F is co-expressed with reelin, a product of Cajal–Retzius neurons that is of fundamental importance in specifying the six-layer structure of the human cortex. HAR1 and the other human accelerated regions provide new candidates in the search for uniquely human biology.
Nature 423, 742-747 (12 June 2003)
Pleistocene Homo sapiens from Middle Awash, Ethiopia
Tim D. White, Berhane Asfaw, David DeGusta, Henry Gilbert, Gary D. Richards, Gen Suwa & F. Clark Howell
Department of Integrative Biology and Laboratory for Human Evolutionary Studies, Museum of Vertebrate Zoology, University of California, Berkeley, California 94720-3160, USA
Rift Valley Research Service, P.O. Box 5717, Addis Ababa, Ethiopia
Laboratory for Human Evolutionary Studies, Museum of Vertebrate Zoology, University of California, Berkeley, California 94720-3160, USA
The University Museum, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
The origin of anatomically modern Homo sapiens and the fate of Neanderthals have been fundamental questions in human evolutionary studies for over a century. A key barrier to the resolution of these questions has been the lack of substantial and accurately dated African hominid fossils from between 100,000 and 300,000 years ago. Here we describe fossilized hominid crania from Herto, Middle Awash, Ethiopia, that fill this gap and provide crucial evidence on the location, timing and contextual circumstances of the emergence of Homo sapiens. Radioisotopically dated to between 160,000 and 154,000 years ago, these new fossils predate classic Neanderthals and lack their derived features. The Herto hominids are morphologically and chronologically intermediate between archaic African fossils and later anatomically modern Late Pleistocene humans. They therefore represent the probable immediate ancestors of anatomically modern humans. Their anatomy and antiquity constitute strong evidence of modern-human emergence in Africa.
Nature 433, 733-736 (17 February 2005)
Stratigraphic placement and age of modern humans from Kibish, Ethiopia
Ian McDougall, Francis H. Brown & John G. Fleagle
Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah 84112, USA
Department of Anatomical Science, Stony Brook University, Stony Brook, New York 11794, USA
In 1967 the Kibish Formation in southern Ethiopia yielded hominid cranial remains identified as early anatomically modern humans, assigned to Homo sapiens. Our preferred estimate of the age of the Kibish hominids is 195 5 kyr, making them the earliest well-dated anatomically modern humans yet described.