How Humans Differ from Other Animals in Their Levels of Morphological Variation

Animal species come in many shapes and sizes, as do the individuals and populations that make up each species. To us, humans might seem to show particularly high levels of morphological variation, but perhaps this perception is simply based on enhanced recognition of individual conspecifics relative to individual heterospecifics. We here more objectively ask how humans compare to other animals in terms of body size variation. We quantitatively compare levels of variation in body length (height) and mass within and among 99 human populations and 848 animal populations (210 species). We find that humans show low levels of within-population body height variation in comparison to body length variation in other animals. Humans do not, however, show distinctive levels of within-population body mass variation, nor of among-population body height or mass variation. These results are consistent with the idea that natural and sexual selection have reduced human height variation within populations, while maintaining it among populations. We therefore hypothesize that humans have evolved on a rugged adaptive landscape with strong selection for body height optima that differ among locations

Possible causes of data model discrepancy in the temperature history of the last Millennium

Model simulations and proxy-based reconstructions are the main tools for quantifying pre-instrumental climate variations. For some metrics such as Northern Hemisphere mean temperatures, there is remarkable agreement between models and reconstructions. For other diagnostics, such as the regional response to volcanic eruptions, or hemispheric temperature differences, substantial disagreements between data and models have been reported. Here, we assess the potential sources of these discrepancies by comparing 1000-year hemispheric temperature reconstructions based on real-world paleoclimate proxies with climate-model-based pseudoproxies. These pseudoproxy experiments (PPE) indicate that noise inherent in proxy records and the unequal spatial distribution of proxy data are the key factors in explaining the data-model differences. For example, lower inter-hemispheric correlations in reconstructions can be fully accounted for by these factors in the PPE. Noise and data sampling also partly explain the reduced amplitude of the response to external forcing in reconstructions compared to models. For other metrics, such as inter-hemispheric differences, some, although reduced, discrepancy remains. Our results suggest that improving proxy data quality and spatial coverage is the key factor to increase the quality of future climate reconstructions, while the total number of proxy records and reconstruction methodology play a smaller role

Global surface-temperature responses to major volcanic eruptions

The impacts of pollution resulting from large explosive volcanic eruptions on the atmospheric heat budget and planetary albedo are not in doubt. However, the effects of volcanic aerosols on the surface climate are less clear and still controversial. In a previous study it was shown that significant surface cooling occurs over the landmasses of the Northern Hemisphere in the first few months after a major eruption in that hemisphere. Here we extend that work using new surface-air temperature compilations based on land and marine data for both the Northern and Southern Hemispheres. Our results indicate that major Northern Hemisphere average surface temperature but little or no effect on the Southern Hemisphere average.Southern Hemisphere eruptions affect both Southern and Northern Hemisphere temperatures after a lag of between six months and a year

Variations in surface atemperatures: Part 2. Arctic regions, 1881–1980

We describe annual and seasonal changes in air temperatures over high latitudes of the Northern Hemisphere during the period 1881–1980. Trends (that is, fluctuations on time scales greater than 20 years) in the average temperature of the Arctic are compared with those of the Northern Hemisphere. Seasonal and regional departures from the long-term trends in the average temperature of the Arctic are identified. Spatial patterns of variation in the Arctic temperature field are determined by principal component analysis and the major characteristics of the time series of the dominant patterns are summarized. Trends in Arctic temperatures have been broadly similar to those for the Northern Hemisphere during the study period. The Arctic variations were, however, greater in magnitude and more rapid. The spatial pattern of change associated with the trend in Arctic temperatures is clearly identified by principal component analysis. It shows that the trends have, in general, been Arctic-wide, but that certain regions are particularly sensitive to long-term variations, most notably northwest Greenland and around the Kara Sea. There is some evidence that the pattern of Arctic cooling that occurred after 1940 was more complex than the warming that affected the whole Arctic during the 1920's and 1930's. Warming of the Arctic has occurred during the 1970's, but is not yet of sufficient duration to be considered long term, except, perhaps, in spring. The average temperature of the Arctic during the 1970's was equal to that of the 1960's, indicating a cessation of the long-term cooling trend but not, as yet, a shift to long-term warming. Short-term variations in temperature appear to be most pronounced close to major regions of sea-ice production and decay

The Reproductive Ecology of Industrial Societies, Part I : Why Measuring Fertility Matters.

Is fertility relevant to evolutionary analyses conducted in modern industrial societies? This question has been the subject of a highly contentious debate, beginning in the late 1980s and continuing to this day. Researchers in both evolutionary and social sciences have argued that the measurement of fitness-related traits (e.g., fertility) offers little insight into evolutionary processes, on the grounds that modern industrial environments differ so greatly from those of our ancestral past that our behavior can no longer be expected to be adaptive. In contrast, we argue that fertility measurements in industrial society are essential for a complete evolutionary analysis: in particular, such data can provide evidence for any putative adaptive mismatch between ancestral environments and those of the present day, and they can provide insight into the selection pressures currently operating on contemporary populations. Having made this positive case, we then go on to discuss some challenges of fertility-related analyses among industrialized populations, particularly those that involve large-scale databases. These include "researcher degrees of freedom" (i.e., the choices made about which variables to analyze and how) and the different biases that may exist in such data. Despite these concerns, large datasets from multiple populations represent an excellent opportunity to test evolutionary hypotheses in great detail, enriching the evolutionary understanding of human behavior

Recent temperature changes in the Arctic and Antarctic

The possibility of a global warming induced by increasing levels of atmospheric carbon dioxide has led to increased interest in monitoring global temperatures. Polar regions are of particular interest because temperature changes may be amplified in these regions by the complex feedback mechanisms which operate in the atmosphere-ice-ocean system1. Monthly mean station surface air-temperature data have been objectively analysed to produce time series of temperature anomalies for the Northern Hemisphere (1881-1980)2,3, the Arctic (1881-1980)4 and the Antarctic (1957-82)5. A comparison of recent changes in these three regions is made here. Previously published series have been updated to 1982. Changes in Arctic temperatures since about 1966 and in Antarctic temperatures since 1960 show significant warming trends. For the period from 1975 to 1982 there is a high positive correlation between temperature variations in the Arctic and Antarctic

Climatic reconstruction of two Pliocene floras from Mexico

The role that climate plays in influencing the physiognomy of modern and fossil plant communities is widely acknowledged and forms the basis for several palaeoclimate proxies. In this work, both univariate Leaf Margin Analysis and multivariate Climate/Leaf Analysis Multivariate Program (CLAMP) were used for the climatic reconstruction of two fossil localities of the Atotonilco El Grande Formation. Using the predominantly North American and Asian calibration data set PHYSG3BRC, supplemented with new African material, results from two sites, Los Baños (present position 20°18′18″N, 98°42′44.4″W) and Sanctorum (20°18′18.5″N and 98°46′52.2″W), indicate that during the Pliocene a mesothermal climate existed with mean annual temperatures between 12 and 22°C, with the most likely being approximately 15°C, and a mean annual temperature range of 21°C. A distinct seasonal variation in rainfall is evident with a mean annual relative humidity of 60–70%. Differences between the sites can be explained by differences in depositional regime and spatial heterogeneity in the predominantly Quercus-dominated woodland. The continuous subsequent uplift of the Sierra Madre Oriental, the resulting development of a rain shadow, and the eventual disappearance of a palaeolake appear to have caused a transition to the modern xerophytic shrub vegetation