Homo erectus and Middle Pleistocene hominins: Brain size, skull form, and species recognition
G. Philip Rightmire
Hominins that differ from Homo erectus, the Neanderthals, and recent humans are known from Middle Pleistocene localities across the Old World. The taxonomic status of these populations has been clouded by controversy. Perhaps the most critical problem has been an incomplete understanding of variation in skull form. Here, both H. erectus and later mid-Pleistocene hominins are the focus of an investigation aimed at clarifying the relationships among brain volume, basicranial dimensions, neurocranial shape, and certain facial characters. Brain size in H. erectus averages about 950 cm3, while in a series of Middle Pleistocene crania from Africa and Europe, volume is about 1230 cm3. If encephalization is the primary mechanism operating in the mid-Pleistocene, then diverse aspects of cranial form cannot all be treated as independent variables. Correlation is utilized to examine the associations among measurements for more than 30 H. erectus crania that are reasonably well preserved. A similar approach is used with the Middle Pleistocene sample. Patterns of covariation are compared in order to assess integration. Next, factor analysis is applied to the H. erectus specimens in an attempt to identify modules, tightly integrated traits that can evolve independently. Studies of the variation within H. erectus are followed by direct comparisons with the Middle Pleistocene population. Discriminant functions facilitate the description of intergroup differences. Traits that vary independently from brain volume include anterior frontal broadening, lateral expansion of the parietal vault, elevation of the lambda–inion chord, and rounding of the sagittal contour of the occipital. This finding helps to resolve the problem of species recognition. Neurocranial proportions as well as characters from the cranial base and face can be incorporated into a differential diagnosis for the mid-Pleistocene sample. Evidence presented here supports arguments for speciation in the Middle Pleistocene.
Late Pleistocene climate change and the global expansion of anatomically modern humans
Eriksson et al.
Published online before print September 17, 2012, doi: 10.1073/pnas.1209494109
The extent to which past climate change has dictated the pattern and timing of the out-of-Africa expansion by anatomically modern humans is currently unclear [Stewart JR, Stringer CB (2012) Science 335:1317–1321]. In particular, the incompleteness of the fossil record makes it difficult to quantify the effect of climate. Here, we take a different approach to this problem; rather than relying on the appearance of fossils or archaeological evidence to determine arrival times in different parts of the world, we use patterns of genetic variation in modern human populations to determine the plausibility of past demographic parameters. We develop a spatially explicit model of the expansion of anatomically modern humans and use climate reconstructions over the past 120 ky based on the Hadley Centre global climate model HadCM3 to quantify the possible effects of climate on human demography. The combinations of demographic parameters compatible with the current genetic makeup of worldwide populations indicate a clear effect of climate on past population densities. Our estimates of this effect, based on population genetics, capture the observed relationship between current climate and population density in modern hunter–gatherers worldwide, providing supporting evidence for the realism of our approach. Furthermore, although we did not use any archaeological and anthropological data to inform the model, the arrival times in different continents predicted by our model are also broadly consistent with the fossil and archaeological records. Our framework provides the most accurate spatiotemporal reconstruction of human demographic history available at present and will allow for a greater integration of genetic and archaeological evidence.
Video coverage of Did Climate Change Shape Human Evolution? – meeting at Lamont in March 2012.
‘Red Deer Cave people’ may be new species of human
Stone age remains of people with a penchant for home-cooked venison could represent a new human evolutionary line
Human Remains from the Pleistocene-Holocene Transition of Southwest China Suggest a Complex Evolutionary History for East Asians
Energetics and the evolution of human brain size
Carel P. van Schaik
Journal name: Nature
Date published: 01 December 2011
The human brain stands out among mammals by being unusually large. The
expensive-tissue hypothesis1 explains its evolution by proposing a trade-off
between the size of the brain and that of the digestive tract, which is
smaller than expected for a primate of our body size. Although this
hypothesis is widely accepted, empirical support so far has been equivocal.
Here we test it in a sample of 100 mammalian species, including 23 primates,
by analysing brain size and organ mass data. We found that, controlling for
fat-free body mass, brain size is not negatively correlated with the mass of
the digestive tract or any other expensive organ, thus refuting the
expensive-tissue hypothesis. Nonetheless, consistent with the existence of
energy trade-offs with brain size, we find that the size of brains and
adipose depots are negatively correlated in mammals, indicating that
encephalization and fat storage are compensatory strategies to buffer
against starvation. However, these two strategies can be combined if fat
storage does not unduly hamper locomotor efficiency. We propose that human
encephalization was made possible by a combination of stabilization of
energy inputs and a redirection of energy from locomotion, growth and