European Neandertals were replaced by modern human populations from Africa ~40,000 years ago. Archaeological evidence from the best-documented region of Europe shows that during this replacement human populations increased by one order of magnitude, suggesting that numerical supremacy alone may have been a critical factor in facilitating this replacement.

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Demographic change has recently re-emerged as a key explanation for socio-cultural changes documented in the prehistoric archaeological record. While the majority of studies of Pleistocene demography have been conducted by geneticists, the archaeological records of the Palaeolithic should not be ignored as a source of data on past population trends. This paper forms both a comprehensive synthesis and the first critical review of current archaeological research into Palaeolithic demography. Within prevailing archaeological frameworks of dual inheritance theory and human behavioural ecology, I review the ways in which demographic change has been used as an explanatory concept within Palaeolithic archaeology. I identify and discuss three main research areas which have benefitted from a demographic approach to socio-cultural change; 1) technological stasis in the Lower Palaeolithic; 2) the Neanderthal-Homo sapiens transition in Europe, and; 3) the emergence of behavioural modernity. I then address the ways in which palaeodemographic methods have been applied to Palaeolithic data-sets, considering both general methodological concerns and the challenges specific to this time period. Finally, I discuss the ability of ethnographic analogy to aid research into Palaeolithic demography.

a b s t r a c tRadiocarbon date frequency distributions and archaeological site counts are two popular proxies used to investigate prehistoric demography, following the assumption that variations in these data reflect fluctuations in the relative size and distribution of past populations. However, the two approaches are rarely applied to the same data-set and their applicability is heavily conditioned by the archaeological record in question, particularly research histories, agendas, and funding availability. In this paper we use both types of data to examine the population history of the Upper Palaeolithic hunteregatherers (~40 000e12 000 cal BP) of Southwestern France, comparing the demographic signatures generated.Both proxies produce similar signatures across the Upper Palaeolithic sequence of the region, strengthening the interpretation of relative demographic changes as the cause of the pattern. In particular, a marked population decline is seen in both datasets during the Late Gravettian (~28 000 cal BP), as well as a population increase in the Late Solutrean (~25 000 cal BP) supporting the notion that the region acted as a population refugium during the Last Glacial Maximum. Where the two proxies diverge in the demographic signatures they produce, the radiocarbon date distribution shows peaks compared to troughs in site counts; the opposite pattern expected given taphonomic issues surrounding cultural carbon. Despite differences in chronological resolution and sampling bias, our data suggest that the two proxies can be considered broadly equivalent; a finding which warrants the investigation of prehistoric demography in regions where either extensive survey data or radiometric dating programmes are unavailable. While some preliminary observations are made, the impact of changing mobility on diachronic patterns seen in both proxies remains, however, difficult to assess.

Archaeological evidence suggests that important shifts were taking place in the character of human social behaviours 300,000 to 30,000 years ago. New artefact types appear and are disseminated with greater frequency. Transfers of both raw materials and finished artefacts take place over increasing distances, implying larger scales of regional mobility and more frequent and friendlier interactions between different communities. Whilst these changes occur during a period of increasing environmental variability, the relationship between ecological changes and transformations in social behaviours is elusive. Here, we explore a possible theoretical approach and methodology for understanding how ecological contexts can influence selection pressures acting on intergroup social behaviours. We focus on the relative advantages and disadvantages of intergroup tolerance in different ecological contexts using agent-based modelling (ABM). We assess the relative costs and benefits of different ‘tolerance’ levels in between-group interactions on survival and resource exploitation in different environments. The results enable us to infer a potential relationship between ecological changes and proposed changes in between-group behavioural dynamics. We conclude that increasingly harsh environments may have driven changes in hormonal and emotional responses in humans leading to increasing intergroup tolerance, i.e. transformations in social behaviour associated with ‘self-domestication’. We argue that changes in intergroup tolerance is a more parsimonious explanation for the emergence of what has been seen as ‘modern human behaviour’ than changes in hard aspects of cognition or other factors such as cognitive adaptability or population size.

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Photorefraction of a sample of 93 infants of ages 1 day to 12 months showed that 63 percent of the subjects had astigmatism of 0.75 diopter or greater, and 12 percent greater than 2 diopters. Seventy percent of these astigmatisms were in the horizontal-vertical meridians. By comparison, only 8 percent of a sample of 26 adults tested by the same method showed astigmatism (all 0.75 to 1 diopter). The high incidence of infant astigmatism has implications for critical periods in human visual development and for infant acuity.

SUMMARY A procedure specifically adapted for children of preschool age has been used to measure contrast sensitivity in emmetropic children aged 3 to 5 years. Mothers of the children acted as adult observers using the same procedure. The results show that the contrast sensitivity function of adults and children is very similar, sensitivity for the children being slightly lower than that for adults at all spatial frequencies. The sensory and cognitive factors involved in these differences are discussed. including acuity, in the first 6 months of life. Presumably the subsequent development to adult levels is more gradual. From measurements that have been reported on children of school age it seems that there is still a difference in contrast sensitivity between these children and adults.'8Here we investigate how close the vision of the preschool child is to that of the adult using the same test for both. A preliminary account of our overall results has already been presented.'9 We now describe the procedure and give a fuller analysis of the findings. Materials and methods STIMULIThe stimuli were black-and-white grating patterns mounted on the inner surfaces of transparent acrylic cubes (7-6 cm high by 8'9 cm wide) of the type commercially available for displaying photographs. For measurements of contrast sensitivity the gratings were black-and-white photographic prints of sinusoidal grating patterns taken from an oscilloscope screen, with care being taken in exposure and processing to obtain prints whose density was a linear function of the original light intensity. A set of prints was used whose contrast ranged from 0 75 % to 47 %. Spatial frequencies of 0-3, 15, and 3 cycles/deg were obtained by presenting the same cubes at 30 cm, 15 m, and 3 m. The acuity point on the contrast sensitivity function was determined, by using high-contrast square-wave gratings made from Letraset sheet no.