Wednesday, 31 October 2012

Infection Breeds Reticence: The Effects of Disease Salience on Self-Perceptions of Personality and Behavioral Avoidance Tendencies

Chad R. Mortensen, D. Vaughn Becker, Joshua M. Ackerman, Steven L. Neuberg, and Douglas T. Kenrick, (2010) Psychological Science 21(3) 440–447

Past research has shown that humans seem to have evolved behavioural mechanisms for reducing risk of infection form communicable disease. This paper looks to examine this experimentally. Undergraduate students exposed to a disease prime led participants to rate themselves as less extroverted than did exposure to a control prime, and those who thought they were particularly vulnerable to disease also rated themselves as less agreeable and less open to new experiences. Behavioural differences were also found. Past research also suggests that this kind of avoidance, as well as ethnocentrism and various in-group out group behaviours, are also triggered by observing people with other types of physical abnormalities, even when there is no infectious  disease or parasite involved - such as when confronted with physically disabled or obese individuals. Could the recent staggering rise in obesity in the developed world, particularly in the US, partly explain increased prevalence of attitudes and political beliefs tending towards ethnocentrism, illiberal attitudes and the rise of the conservative right?  Hmmm . . .

Radiocarbon dates from the Grotte du Renne and Saint-Césaire support a Neandertal origin for the Châtelperronian.

Hublin, J.-J., Talamo, S., Julien, M., David, F., Connet, N., Bodu, P., Vandermeersch, B., Richards, M.P., 2012. PNAS.

The Chatelperronian is a so-called ‘transitional industry’ between Middle Palaeolithic (MP: definitely associated with Neanderthals) and Upper Palaeolithic (UP: almost definitely associated with anatomically modern humans (AMH)) industries in Central/Southwestern France and Northern Spain.  Châtelperronian artefacts have been found in direct association with a Neanderthal fossil at St Césaire. 
However, it has been argued that stratigraphic mixing has created associations between Neanderthal skeletal material, Châtelperronian tools and body ornaments by chance. 
This paper reports new radiocarbon dates from bone for late Mousterian (MP), Châtelperronian and Protoaurignacian (UP) layers at Grotte du Renne and shows that the dates are inconsistent with strata mixing (admixture), contrary to previous work (Higham et al 2011 PNAS).  They also directly date St Césaire (41-95 – 40.66ky calBP).  Their dates place the Châtelperronian body ornaments (~41ky calBP) as post-dating AMH dispersals into adjacent areas (e.g. 43–42kyr cal bp in Kent: Higham et al 2011, Nature) and therefore argue that this ‘innovation’ could be the result of acculturation (cultural diffusion from AMH) rather than independent innovation.  However, the two apparent 50ky-old pigmented shell ornaments from Spain pre-date the current earliest dates for AMH in Europe ( 

Thursday, 25 October 2012

The Date of Interbreeding between Neandertals and Modern Humans.

Sankararaman, S., Patterson, N., Li, H., Pääbo, S., Reich, D., 2012. PLoS Genet 8, e1002947.

The authors use the extent of linkage disequilibrium (the association between two or more loci – the distance of DNA that hasn’t been broken up by recombination, which is reduced over time) in modern humans to test between two models (i) Neanderthal (or their close kin)-AMH interbreeding (Neanderthal gene flow) versus (ii) ancient sub-structuring in the ancestral population in Africa.  They find evidence for the former and date the last gene flow from Neanderthals to AMH to 37-986kyaBP.  Taking the possibility of both ancient sub-structuring and gene flow into account yields dates of 47-65kya.




Wednesday, 24 October 2012

Metabolic constraint imposes tradeoff between body size and number of brain neurons in human evolution

This recently published PNAS article constitutes the first experimental evidence of Wrangham's hypothesis concerning the importance of cooking in human brain evolution. The article notes that our brains consume about 20% of our body's metabolic energy, compared to 9% in other primates, raising the question as to how we could afford to feed such metabolically expensive organs. The paper argues cooking bridged this gap, following several lines of evidence, including: 1) brain size is directly linked to the number of neurons in the brain and 2) the number of neurons is directly correlated to the amount of energy (or calories) needed to feed a brain. After adjusting for body mass, they calculated how many hours per day it would take for various primates to eat enough calories for uncooked food to fuel their brains: 8.8 hours for gorillas, 7.8 hours for orangutans, 7.3 hours for chimps, and a whopping 9.3 hours for Homo sapiens. In sum, the paper seems to make a relatively good case that cooking lifted an important constraint on human brain evolution. However, what seems much less clear, based on these results is whether cooking itself was responsible for the first dramatic burst of brain growth and how, by itself, may or may not have driven this expansion. Thus, Wrangham's more modest claim seems supported, while his more extreme claim does not.

Here is a link to the article:

As well as an interesting Science news blurb summarizing most of the important points:

Thursday, 18 October 2012

Taphonomy of Ungulate Ribs and the Consumption of Meat and Bone by 1.2-Million-Year-Old Hominins at Olduvai Gorge, Tanzania.

Pickering, T.R., Domínguez-Rodrigo, M., Heaton, J.L., Yravedra, J., Barba, R., Bunn, H.T., Musiba, C., Baquedano, E., Diez-Martín, F., Mabulla, A., Brain, C.K., 2012. Journal of Archaeological Science. 

This paper compares ungulate ribs from Oluvai dated ~1.2mya with those butchered and eaten by modern hunter-gatherers as well as with carnivore assemblages.  They suggest that further to tooth- and cut-marks found on the Olduvai bones the ‘peeling back’ of the rib outer surface is another hallmark of hominin activity also seen in modern human rib processing (and in chimp, but only very rarely in carnivore, rib eating).  They argue that carnivores target the organs contained in the rib cage so the fact that hominins seem to have had primary access to ribs suggests that they were actively hunting and defending prey from other carnivores or driving away carnivores from fresh kills. Interestingly, as Tamas pointed out, the authors do not mention charred bones, meaning there is no evidence of cooking in this assemblage.

Earliest Porotic Hyperostosis on a 1.5-Million-Year-Old Hominin, Olduvai Gorge, Tanzania.

Domínguez-Rodrigo, M., Pickering, T.R., Diez-Martín, F., Mabulla, A., Musiba, C., Trancho, G., Baquedano, E., Bunn, H.T., Barboni, D., Santonja, M., Uribelarrea, D., Ashley, G.M., Martínez-Ávila, M.d.S., Barba, R., Gidna, A., Yravedra, J., Arriaza, C., 2012. PLoS ONE 7, e46414.  

Fragments of right parietal of a ~2year-old from 1.5mya site at Olduvai shows signs of porotic hyperostosis, which suggests anemia, a condition most common at weaning (although also associated with malaria).  This condition is virtually unknown in chimpanzees.  The authors suggest that this find provides evidence for a substantial meat component to the diet of the hominins this infant represents.


Revising the human mutation rate: implications for understanding human evolution.

Scally, A., Durbin, R., 2012. Nat Rev Genet 13, 745-753. PERSPECTIVE.

Rather than using a phylogenetic approach to estimate the mutation rate to calibrate the ‘molecular clock’ (i.e. using a fossil of a known date to anchor the divergence time between two species) these authors advocate using de novo mutation rates between parent and offspring trios.  This halves the suggested mutation rate to 0.5x10-9 bp-1 year-1, although this depends on generation time.  Using this rate they re-calculate (i) the Neanderthal-AMH divergence to ~500kya, which is inline with mtDNA estimates, (ii) the split between Khoe-San and other modern humans to 250-300kya (which is older than the single locus estimates for the root of the human tree and requires re-evalaution of the models of dispersion across the globe), (iii) the split between the Yoruba and non-Africans to 90-130kya (meaning the Skhul-Qafzeh population might not be an earlier ‘failed dispersion’ population after all and potentially giving Middle Eastern Neanderthals and AMH a longer period of interbreeding) and (iv) European-Asia split re-dated to 40-80kya.  The revised mutation rate doubles the effective population size parameter, which again may affect previous models of AMH dispersals out of Africa. 


Generation times in wild chimpanzees and gorillas suggest earlier divergence times in great ape and human evolution.

Langergraber, K.E., Prüfer, K., Rowney, C., Boesch, C., Crockford, C., Fawcett, K., Inoue, E., Inoue-Muruyama, M., Mitani, J.C., Muller, M.N., Robbins, M.M., Schubert, G., Stoinski, T.S., Viola, B., Watts, D., Wittig, R.M., Wrangham, R.W., Zuberbühler, K., Pääbo, S., Vigilant, L., 2012. Proceedings of the National Academy of Sciences. 

This paper uses chimpanzee, gorilla and human generation times and new estimates of the average human mutation rate (based on parent-child trios) to estimate the chimp-human divergence time as occurring ~7-13mya, which is more inline with fossil-based indications than previous genetic-based divergence times of ~4-6mya.  Furthermore, the authors calculate the Neanderthal-AMH divergence as ~400-700kya (versus previous genetic-based estimates of ~200-400ky), which again is more inline with fossils such as Sima de Los Huesos and Swancombe, which already seem to show Neanderthal-like traits at ~600ky (although this early date is debated) and ~400ky respectively.