Systematic Biology T-Shirts
Everyone's favorite systematics journal Systematic Biology have produced a collection of T-Shirts that you can buy online (like the awesome one above). This is a fundraising project, and 100% of the profits will go to helping graduate students in the field of systematic biology (like me!).
There are others there that aren't official SB-products, but are still tempting...
Sexual Selection Has Shaped the Hominin Face
Weston et al in PLoS One show that sexual selection has shaped the Hominin face (doi:10.1371/journal.pone.0000710):
We consider sex differences in human facial morphology in the context of developmental change. We show that at puberty, the height of the upper face, between the lip and the brow, develops differently in males and females, and that these differences are not explicable in terms of sex differences in body size.
We find the same dimorphism in the faces of human ancestors. We propose that the relative shortening in men and lengthening in women of the anterior upper face at puberty is the mechanistic consequence of extreme maxillary rotation during ontogeny. A link between this developmental model and sexual dimorphism is made for the first time, and provides a new set of morphological criteria to sex human crania.
This finding has important implications for the role of sexual selection in the evolution of anthropoid faces and for theories of human facial attractiveness.
Their results suggest that facial attractiveness played a major role in human evolution.
Baby, I’m no Fred Flintstone, but I can make your Bedrock!
PsyBlog reviews the psychological research on pick-up lines:
Indeed, a study by Chris Bale from the University of Central Lancashire
found that sexually-loaded remarks were the type of openers least
likely to lead to further interaction (Bale, 2006). Which begs the
question: why do men still use them?...Chat-up lines may be a way for men to select for
a particular type of woman. In other words, men using sexually-loaded
remarks are looking for a certain type of woman (an easy one).
Similarly, at the other end of the scale, men who use
character-revealing or culture-based openers are probably trying to
show they are a good mate looking for a long-term partner.
I'd be most interested to hear what the ladies think of this, as well as any top-notch lines that you've encountered?
Neolithic settlement of Europe, fractal network theory and hunter-gatherers, & rapid butterfly evolution
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.
Did color vision cause social mating systems in primates?
Why do primates have color vision? One of the leading theories over the last few years is that primates evolved trichromatic color vision to better detect fruits (generally red or orange colored) from leaves (primarily green). However, others have argued that the cause was to enhance intra-specific signalling, primarily to recognise the reddened skin regions which can signal sexual arousal/fecundity.
A study out in American Naturalist, Sexual Selection and Trichromatic Color Vision in Primates: Statistical Support for the Preexisting-Bias Hypothesis by Fernandez and Morris, investigates this. Using a large phylogeny of primates, the authors reconstructed the characteristics in question on the tree, and show that trichromatic color vision evolved deep in the tree (prior to the Tarsiidae-platyrrhine-catarrhine split), which is before the evolution of gregarious mating systems (which appear to have arisen prior to the Old World monkey split).
These results suggest that color vision evolved first, but then became exapted for intraspecific communication. What's more, the use of reddened skin color as a sexual marker is more likely to evolve in the primate lineages with color vision and lead to gregarious social mating systems. That is, color vision appears to have played a role in allowing gregarious mating systems to have evolved in primates.
The abstract:
The evolution of trichromatic color vision in primates may improve foraging performance as well as intraspecific communication; however, the context in which color vision initially evolved is unknown. We statistically examined the hypothesis that trichromatic color vision in primates represents a preexisting bias for the evolution of red coloration (pelage and/or skin) through sexual selection. Our analyses show that trichromatic color vision evolved before red pelage and red skin, as well as before gregarious mating systems that would promote sexual selection for visual traits and other forms of intraspecific communication via red traits. We also determined that both red pelage and red skin were more likely to evolve in the presence of color vision and mating systems that promote sexual selection. These results provide statistical support for the hypothesis that trichromatic color vision in primates evolved in a context other than intraspecific communication with red traits, most likely foraging performance, but, once evolved, represented a preexisting bias that promoted the evolution of red traits through sexual selection.
Intersexual arms race in diving beetles
One of Darwin's pet examples of sexual selection were the Diving Beetles, where he argued that the male and female members of the same species co-evolved their mating techniques (i.e. males with large suction cups to hold the females).
However, it appears that this is more of an inter-sex arms race, where the females develop modifications of their dorsal surface to hinder the male suction cups:
To trace the evolutionary history of sex-specific characters in diving beetles, we used the recently revised genus Acilius which contains 13 extant species distributed over the Northern Hemisphere. The genus is characterized by having dense macropunctures on the dorsal surfaces, females with prominent, setose furrows on the elytra, and males with broadly expanded protarsi equipped ventrally with three large and many minute suction cups. These structures even attracted the attention of Charles Darwin, who regarded the setose female furrows in Acilius as an example of an aid for males to better grip females during mating. However, it is clear from basic physical laws and simple experiments, that the mechanically working male suction cups function best on smooth surfaces where complete contact around their circumference enables attachment.
Continued at Phylogeny of Diving Beetles Reveals a Coevolutionary Arms Race between the Sexes.