Sally McBrearty

Bio: Sally McBrearty is an academic researcher from University of Connecticut. The author has contributed to research in topics: Middle Stone Age & Stone tool. The author has an hindex of 17, co-authored 25 publications receiving 3598 citations. Previous affiliations of Sally McBrearty include Brandeis University & College of William & Mary.

Tools underfoot : Human trampling as an agent of lithic artifact edge modification

Abstract: A series of eight replication experiments tests the proposition that human trampling of stone flakes can produce edge damage that mimics deliberate retouch. Retouchlike edge damage, breakage, and other forms of macroscopic mechanical damage were observed on large numbers of pieces in all trampled sets. Experiments measured the relative contributions of three variables-raw material, artifact density, and substrate-in generating damage. Results indicate that while all three factors contribute to some degree, substrate plays the most decisive role, and that artifacts are more likely to exhibit damage if trampled on an impenetrable substrate. It was further found that trampling transforms flakes into pseudo-tools that can be classified as formal tools using a standard typology. Many of these are notched and denticulate pieces, indicating that special caution is needed in behavioral interpretations based on these tool types, and that the European Paleolithic Denticulate Mousterian industry requires critical reassessment.

Levallois Lithic Technology From the Kapthurin Formation, Kenya: Acheulian Origin and Middle Stone Age Diversity

Abstract: The earliest fossils of Homo sapiens are reported from in Africa in association with both late Acheulian and Middle Stone Age (MSA) artifacts. The relation between the origin of our species during the later Middle Pleistocene in Africa and the major archaeological shift marked by the Acheulian-MSA transition is therefore a key issue in human evolution, but it has thus far suffered from a lack of detailed comparison. Here we initiate an exploration of differences and similarities among Middle Pleistocene lithic traditions through examination of Levallois flake production from a sequence of Acheulian and MSA sites from the Kapthurin Formation of Kenya dated to ∼200–500 ka. Results suggest that MSA Levallois technology developed from local Acheulian antecedents, and support a mosaic pattern of lithic technological change across the Acheulian-MSA transition. Les premiers restes fossiles d’Homo sapiens sont rapportes d’Afrique aussi bien a des avec des outillages de l’Acheuleen final que du Middle Stone Age (MSA). La relation entre l’origine de notre espece au Pleistocene moyen final d’Afrique et le changement majeur marquee par la transition Acheuleen-MSA est par consequent un moment cle de l’evolution humaine qui a manque jusqu’ici d’analyses comparatives detaillees. Nous nous proposons ici de commencer a explorer les differences et les similarites qui peuvent se faire jour au Pleistocene moyen dans les traditions techniques a l’examen des productions a eclats Levallois, dans une sequence de sites acheuleens et MSA de la formation de Kapthurin (Kenya), datee de 200–500 ka. Les resultants obtenus suggerent que la technologie Levallois MSA s’est developpee sur ce substrat acheuleen et renforce cette perception que l’on peut avoir d’une mosaique de changements technologiques jalonnant la transition Acheuleen-MSA.

First fossil chimpanzee

Abstract: The cover photo by Kevin Langergraber shows the adult female chimpanzee ‘Jolie’ in Kibale National Park, Uganda. This was taken on 16 August 2004, a few weeks before Jolie gave birth to her first infant. This week marks a landmark in the study of our closest living relative: the publication by the Chimpanzee Sequencing and Analysis Consortium of the initial sequence of the chimpanzee genome, together with a comparison with the human genome. The paper describes changes that have shaped human and chimpanzee species since the split from our common ancestor, and hints at what makes us uniquely human: 35 million single-nucleotide substitutions, 5 million small insertions and deletions, local rearrangements and a chromosome fusion. A comparison of gene duplications in chimpanzee and human genomes reveals gene expression differences that may underlie disease susceptibility. A study of primate genomes shows that subtelomeres are hot spots of recent chromosomal duplication and gene conversion. Conservation of Y-linked genes during human evolution is revealed by comparative sequencing in the chimpanzee. The final research paper in this collection fills a big gap in our knowledge: the first chimpanzee fossils ever found show that chimps and early humans inhabited the same environments in which they evolved and diverged. The fossils — three teeth — are from half-million-year-old sediments in Kenya that also yielded fossils of Homo. Four Progress reviews accompany these papers, looking at chimp culture, social behaviour, psychology and cognition. Elsewhere in the issue, researchers talk about working with chimpanzees, a feature summarizes other primate genome projects, and in two Commentaries, important ethical issues surrounding research on great apes are considered. There are thousands of fossils of hominins, but no fossil chimpanzee has yet been reported. The chimpanzee (Pan) is the closest living relative to humans1. Chimpanzee populations today are confined to wooded West and central Africa, whereas most hominin fossil sites occur in the semi-arid East African Rift Valley. This situation has fuelled speculation regarding causes for the divergence of the human and chimpanzee lineages five to eight million years ago. Some investigators have invoked a shift from wooded to savannah vegetation in East Africa, driven by climate change, to explain the apparent separation between chimpanzee and human ancestral populations and the origin of the unique hominin locomotor adaptation, bipedalism2,3,4,5. The Rift Valley itself functions as an obstacle to chimpanzee occupation in some scenarios6. Here we report the first fossil chimpanzee. These fossils, from the Kapthurin Formation, Kenya, show that representatives of Pan were present in the East African Rift Valley during the Middle Pleistocene, where they were contemporary with an extinct species of Homo. Habitats suitable for both hominins and chimpanzees were clearly present there during this period, and the Rift Valley did not present an impenetrable barrier to chimpanzee occupation.

Taphonomic and Ecologic Information Form Bone Weathering

Abstract: Bones of recent mammals in the Amboseli Basin, southern Kenya, exhibit distinctive weathering characteristics that can be related to the time since death and to the local conditions of temperature, humidity and soil chemistry. A categorization of weathering characteristics into six stages, recognizable on descriptive criteria, provides a basis for investigation of weathering rates and processes. The time necessary to achieve each successive weathering stage has been calibrated using known-age carcasses. Most bones decompose beyond recognition in 10 to 15 yr. Bones of animals under 100 kg and juveniles appear to weather more rapidly than bones of large animals or adults. Small-scale rather than widespread environmental factors seem to have greatest influence on weathering characteristics and rates. Bone weathering is potentially valuable as evidence for the period of time represented in recent or fossil bone assemblages, in- cluding those on archeological sites, and may also be an important tool in censusing populations of animals in modern ecosystems.

The Simons Genome Diversity Project: 300 genomes from 142 diverse populations

Abstract: Here we report the Simons Genome Diversity Project data set: high quality genomes from 300 individuals from 142 diverse populations. These genomes include at least 5.8 million base pairs that are not present in the human reference genome. Our analysis reveals key features of the landscape of human genome variation, including that the rate of accumulation of mutations has accelerated by about 5% in non-Africans compared to Africans since divergence. We show that the ancestors of some pairs of present-day human populations were substantially separated by 100,000 years ago, well before the archaeologically attested onset of behavioural modernity. We also demonstrate that indigenous Australians, New Guineans and Andamanese do not derive substantial ancestry from an early dispersal of modern humans; instead, their modern human ancestry is consistent with coming from the same source as that of other non-Africans.

The Coevolution of Parochial Altruism and War

Abstract: Altruism—benefiting fellow group members at a cost to oneself—and parochialism—hostility toward individuals not of one9s own ethnic, racial, or other group—are common human behaviors. The intersection of the two—which we term “parochial altruism”—is puzzling from an evolutionary perspective because altruistic or parochial behavior reduces one9s payoffs by comparison to what one would gain by eschewing these behaviors. But parochial altruism could have evolved if parochialism promoted intergroup hostilities and the combination of altruism and parochialism contributed to success in these conflicts. Our game-theoretic analysis and agent-based simulations show that under conditions likely to have been experienced by late Pleistocene and early Holocene humans, neither parochialism nor altruism would have been viable singly, but by promoting group conflict, they could have evolved jointly.

Paleontological Evidence to Date the Tree of Life

Abstract: The role of fossils in dating the tree of life has been misunderstood. Fossils can provide good "minimum" age estimates for branches in the tree, but "maximum" constraints on those ages are poorer. Current debates about which are the "best" fossil dates for calibration move to consideration of the most appropriate constraints on the ages of tree nodes. Because fossil-based dates are constraints, and because molecular evolution is not perfectly clock-like, analysts should use more rather than fewer dates, but there has to be a balance between many genes and few dates versus many dates and few genes. We provide "hard" minimum and "soft" maximum age constraints for 30 divergences among key genome model organisms; these should contribute to better understanding of the dating of the animal tree of life.