Back in business, with the new issue of PRS B. First up is Sampietro et al (doi:10.1098/rspb.2007.0465) who used phylogeographic analyses on mtDNA samples (HVRI) from 11 Neolithic remains from Granollers (Catalonia, northeast Spain) dating to around 5500 years ago. They found that their results were consistent with long-term genetic continuity in the Iberian peninsula since Neolithic times, and argue that this is indicative of a dual model of Neolithic spread in Europe: acculturation in Central Europe followed by demic diffusion (i.e. population spread) into southern Europe.

This is followed by an intriguing paper which uses “fractal network theory” to investigate the complex structure of hunter–gatherer social networks (doi:10.1098/rspb.2007.0564):

In nature, many different types of complex system form hierarchical, self-similar or fractal-like structures that have evolved to maximize internal efficiency. In this paper, we ask whether hunter-gatherer societies show similar structural properties. We use fractal network theory to analyse the statistical structure of 1189 social groups in 339 hunter-gatherer societies from a published compilation of ethnographies.

We show that population structure is indeed self-similar or fractal-like with the number of individuals or groups belonging to each successively higher level of organization exhibiting a constant ratio close to 4. Further, despite the wide ecological, cultural and historical diversity of hunter-gatherer societies, this remarkable self-similarity holds both within and across cultures and continents. We show that the branching ratio is related to density-dependent reproduction in complex environments and hypothesize that the general pattern of hierarchical organization reflects the self-similar properties of the networks and the underlying cohesive and disruptive forces that govern the flow of material resources, genes and non-genetic information within and between social groups.

Our results offer insight into the energetics of human sociality and suggest that human social networks self-organize in response to similar optimization principles found behind the formation of many complex systems in nature.

Finally, here’s another example of rapid evolution at work. This time, it’s butterflies (Hypolimnas bolina) in Samoa, who’ve developed a “suppressor” gene to defeat Wolbachia. For those of you who aren’t familiar with the creepiness that is Wolbachia, which is a bacteria that is passed along female insects. To help itself breed, it deliberately screw up sex ratios in host species (in this case by selectively aborting male fetuses) to help itself survive.

The outcome of this selective “pruning” by Wolbachia, meant that in 2001, males made up a grand total of 1% of the butterfly population. However, in the last 5 years, the number of males has shifted back to 40% of the population, as a result of strong selection for host suppressor genes in less than 10 generations.

The original paper is in Science: Extraordinary Flux in Sex Ratio (doi:10.1126/science.1143369) and the BBC has a nice article: Butterfly shows evolution at work.

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