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The human brain is unusually large. It has tripled in size from Australopithecines to modern humans.sup.1 and has become almost six times larger than expected for a placental mammal of human size.sup.2. Brains incur high metabolic costs.sup.3 and accordingly a long-standing question is why the large human brain has evolved.sup.4. The leading hypotheses propose benefits of improved cognition for overcoming ecological.sup.5-7, social.sup.8-10 or cultural.sup.11-14 challenges. However, these hypotheses are typically assessed using correlative analyses, and establishing causes for brain-size evolution remains difficult.sup.15,16. Here we introduce a metabolic approach that enables causal assessment of social hypotheses for brain-size evolution. Our approach yields quantitative predictions for brain and body size from formalized social hypotheses given empirical estimates of the metabolic costs of the brain. Our model predicts the evolution of adult Homo sapiens-sized brains and bodies when individuals face a combination of 60% ecological, 30% cooperative and 10% between-group competitive challenges, and suggests that between-individual competition has been unimportant for driving human brain-size evolution. Moreover, our model indicates that brain expansion in Homo was driven by ecological rather than social challenges, and was perhaps strongly promoted by culture. Our metabolic approach thus enables causal assessments that refine, refute and unify hypotheses of brain-size evolution.Using estimates of metabolic costs of the brain and body, mathematical predictions suggest that the evolution of adult Homo sapiens-sized brains and bodies is driven by ecological rather than social challenges and is perhaps strongly promoted by culture., Author(s): Mauricio González-Forero [sup.1] , Andy Gardner [sup.1] Author Affiliations:(1) School of Biology, University of St Andrews, St Andrews, UKMain The leading hypotheses for the evolution of brain size make [...]

Membranes allow the compartmentalization of biochemical processes and are therefore fundamental to life. The conservation of the cellular membrane, combined with its accessibility to secreted proteins, has made it a [...]

Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily--and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming., Understanding soil biogeochemistry is essential to the stewardship of ecosystem services provided by soils, such as soil fertility (for food, fibre and fuel production), water quality, resistance to erosion and [...]

There is much interest in using embryonic stem cells to regenerate tissues and organs. For this approach to succeed, these stem cells or their derivatives must engraft in patients over [...]

Author(s): Yang Xiang [1, 2]; Benoit Laurent [1, 2]; Chih-Hung Hsu [1, 2]; Sigrid Nachtergaele [3, 4, 5]; Zhike Lu [3, 4, 5]; Wanqiang Sheng [1, 2]; Chuanyun Xu [1, [...]

Author(s): Dolors Ferres-Marco [1, 3]; Irene Gutierrez-Garcia [1, 3]; Diana M. Vallejo [1, 3]; Jorge Bolivar [2]; Francisco J. Gutierrez-Aviño [1]; Maria Dominguez (corresponding author) [1] Correct organ formation depends [...]

Author(s): Eric Debayle (corresponding author) [1]; Brian Kennett [2]; Keith Priestley [3] Differences in the thickness of the high-velocity lid underlying continents as imaged by seismic tomography, have fuelled a [...]

Author(s): A. Dao [1]; A. S. Yaro [1]; M. Diallo [1]; S. Timbine [1]; D. L. Huestis [2]; Y. Kassogue [1]; A. I. Traore [1]; Z. L. Sanogo [1]; D. [...]