What caused the woolly mammoth's extinction? Climate warming in the Holocene might have driven the extinction of this cold-adapted species, yet the species had survived previous warming periods, suggesting that the more-plausible cause was human expansion. Testing these competing hypotheses has been hampered by the difficulty in generating quantitative estimates of the relationship between the mammoth's contraction and the climatic and/or human-induced drivers of extinction. In this study, we combined paleo-climate simulations, climate envelope models (which describe the climate associated with the known distribution of a species--its envelope--and estimate that envelope's position under different climate change scenarios), and a population model that includes an explicit treatment of woolly mammoth-human interactions to measure the extent to which climate changes, increased human pressures, or a combination of both factors might have been responsible. Results show a dramatic decline in suitable climate conditions for the mammoth between the Late Pleistocene and the Holocene, with hospitable areas in the mid-Holocene being restricted mainly to Arctic Siberia, where the latest records of woolly mammoths in continental Asia have been found. The population model results also support the view that the collapse of the climatically suitable area caused a significant drop in mammoth population size, making the animals more vulnerable to increasing hunting pressure from expanding human populations. The coincidence of the collapse of climatically suitable areas and the increase in anthropogenic impacts in the Holocene are most likely to have been the "coup de grÃ¢ce," which set the place and time for the extinction of the woolly mammoth.
Forty-two thousand years ago, during the last glacial advance of the Pleistocene epoch, woolly mammoths thundered across the frozen steppes of the Eurasian continent. The huge beasts thrived on the arid tundra of the last ice age, having adapted to temperatures that would chill the toes off any hairless ape. Yet, by the middle of the Holocene epoch, 6,000 years ago, the glaciers had retreated and the Eurasian woolly mammoth was on the verge of extinction. They were ultimately done in, say David NoguÃ©s-Bravo and colleagues, by climate change--with a helping hand from humans.
While large-scale national psychiatric epidemiologic studies have been conducted in Western industrialized nations [1-3], studies in the Arab world have generally been limited to smaller populations [4-6]. In addition, while exposure to war as a risk factor for the development of mental disorders in military populations has previously been described [7,8], the effect of war upon first onset of a range of mental disorders in civilian populations at a national level has not been explored.
* The Chilean health system underwent a drastic neoliberal reform in the 1980s, with the creation of a dual system: public and private health insurance and public and private provision of health services.
* This reform served as a model for later World Bank-inspired reforms in countries like Colombia.
* The private part of the Chilean health system, including private insurers and private providers, is highly inefficient and has decreased solidarity between rich and poor, sick and healthy, and young and old.
* In spite of serious underfinancing during the Pinochet years, the public health component remains the backbone of the system and is responsible for the good health status of the Chilean population.
* The Chilean health reform has lessons for other countries in Latin America and elsewhere: privatisation of health insurance services may not have the expected results according to neoliberal doctrine. On the contrary, it may increase unfairness in financing and inequitable access to quality care.
Our sex chromosomes have profoundly differentiated since evolving from an ancestral pair of non-sex chromosomes (autosomes). In this study, we first show that X chromosome-derived retrogenes (genes that arose as duplicates of "parental" X-linked genes) are specifically expressed during the meiotic and postmeiotic stages of spermatogenesis, thus functionally replacing their parents during, but also after, the process of male meiotic sex chromosome inactivation (MSCI). We then show that the "export" of retroposed gene copies from the X chromosome started rather recently during mammalian evolution, on the eutherian ("placental" mammal) and marsupial lineages, respectively. This suggests that MSCI--the main driving force for this out of the X gene "movement"--originated around the separation of these two major (therian) mammalian lineages, approximately 180 million years ago. Given that MSCI was likely triggered as soon as the proto-X and -Y chromosomes ceased to recombine (an event that marks the origin of these sex chromosomes), our data also support the recent notion that our sex chromosomes and those of other therians emerged, not in the common ancestor of all mammals, but--probably rather late--in the therian ancestor.