Summary: Olsson et al. (2005)

Animals can learn to associate negative events with environmental stimuli (classical fear conditioning). Race bias and fear condition potentially rely on overlapping neural systems. Therefore, Olsson et al. (2005) aimed to further understanding of basic learning theory and social group interaction by investigating how the mechanisms of fear conditioning apply when humans learn by classical fear conditioning in a sociocultural context. They also assessed whether a bias in fear conditioning extends to social groups defined by race. Prepared fear learning is generally demonstrated as persistence to fear-relevant conditioned stimuli in the learned fear response. They conducted two experiments to test whether fear responses acquired to outgroup and ingroup faces persists during extinction (relative to each other). Their results show that individuals from a racial outgroup are more readily associated with an aversive stimulus. However, Olsson et al. (2005) indicate that this response might be reduced by close, positive interracial contact. They postulate that humans might have evolved a more general preparedness to fear others who are dissimilar to themselves or their social group because such individuals were, historically, more likely to pose a threat.

Summary: Hughes et al. (2010)

It is thought that the human Y chromosome evolved a sex-determining function millions of years ago by gene loss. Given this, theories of decelerating decay predicts that chimpanzee and human male-specific regions on the Y-chromosome (MSY) should not show much divergence. Hughes et al. (2010) accurately and completely sequenced the MSY in the chimpanzee, using large-insert bacterial artificial chromosome clones and iterative mapping and sequencing strategies, in order to compare it to the human MSY. They found differences in sequence structure and gene content, suggesting rapid evolution within the last 6 million years, contrary to the prediction that much divergence should be unlikely. They found that both human and chimp MSY euchromatin is largely comprised of ampliconic and X-degenerate sequence classes but noticed that, while humans have less massive palindromes than chimps, chimps have lost large portions of MSY protein-coding genes and gene families. Hughes et al. (2010) suggest that this divergence in chimp and human MSYs could be driven by four synergistic factors: (1) MSY's role in sperm production; (2) "genetic hitchhiking"; (3) frequent ectopic recombination; and (4) mating behaviour differences. They favour (3): that ectopic recombination between MSY amplicons has sped up MSY structural remodelling in both species. This study is the first to fully compared the Y chromosomes from two closely related species. The importance is two-fold: (1) it provides empirical insight into the evolution of the Y-chromosome; and (2) it provides a test of decelerating decay theories.

Summary: Koboroff et al. (2008)

The two hemispheres of the brain are able to conduct different functions, an ability known as brain lateralization. In birds, brain lateralization has been inferred when a preference to observe a stimulus with one eye ("lateral monocular visual field" is observed. Koboroff et al. (2008) considered that Australian magpies (Gymnorhina tibicen) would show eye preferences when performing anti-predator response. Constant assessment is needed during mobbing behaviour, to make decisions regarding approach, mob or withdraw. They speculated that the left hemisphere would control approach, while the right hemisphere would control withdrawal. However, since mobbing is considered a strong agonistic response, this could be controlled by the right hemisphere (controls intense emotion). Monocular fixations prior to or during performance of mobbing activity in response to perceived predation threat were video recorded. Koboroff et al. (2008) found that, prior to withdrawal, magpies favoured the left eye (85%), while prior to approach, magpies favoured the right eye (72%). Hence, approach in magpies is controlled by the left hemisphere, while withdrawal is favoured by the right hemisphere. They speculate that the left hemisphere is used to process visual inputs prior to approach and the right hemisphere prior to withdrawal. Their results are consistent with hemispheric specialisation in other species, including humans. The relationship between predator-prey interactions and the right hemisphere suggest that the right hemisphere may have, over evolutionary time, organised various anti-predator strategies.

Summary: Sigmund et al. (2010)

Players incur costs when imposing fines on exploiters in 'public goods games'. Even the threat of punishment can increase average pro-social contribution and promote collaborative efforts, yet emergence and stability of costly punishment are problematic. Sigmund et al. (2010) designed a model to compare peer-punishment with pool-punishment, which facilitates the sanctioning of second-order free-riders (those who do not punish exploiters), to determine the most beneficial reward system. The systems are expensive ways to encourage free-riders to cooperate. Spread of second-order free-riders can cause cooperation collapse. Without second-order punishment, the peer-punishment is optimal, but in the presence of second-order punishment, pool-punishers do better. Efficiency is traded for stability. Emergence and stability of costly punishing systems, which regulate common group resources and enforce collaborative efforts, do not require group selection or higher authority prescription. While Sigmund et al. (2010)'s model is minimialistic, it is sound in principle.

Summary: Butlin (1995)

The reinforcement hypothesis suggests that natural selection favours an increase in assortative mating (and thus progress towards speciation, if two divergent populations produce low fitness hybrids in the zone of contact. Butlin (1995) briefly reviews a model proposed by Liou & Price (1994) and an empirical study by Noor (1994). Liou & Price's (1994) study considered secondary contact in sympatry of two divergent stickleback populations, with three possible model outcomes (extinction of one population, permanent mixing of the gene pools or reinforcement and speciation). The model suggested  that reinforcement is likely because the diluting effects of gene flow are absent. Butlin (1995) notes, however, that Liou and Price (1995) did not distinguish between the conditions of zero hybrid fitness and reinforcement and argues that the most questionable aspect of this model is the genetic basis of selection against hybrids. Noor's (1994) study addresses the situation where there is a very low level of gene exchange between two species of Drosophila, finding that hybrid males were sterile but hybrid females were fertile. Noor (1994) found evidence for reinforcement, however, Butlin (1995) notes that, while the result is exciting because of testability, the observation is no stronger evidence for reinforcement than other examples. He does agree that this approach could provide more discriminating predictions, but a larger number of localities has to be examined. Finally, Butlin (1995) indicates that reinforcement is potentially important evolutionary process and suggests that further work will identify it's actual importance.

Summary: Kalueff & Tuohimaa (2005)

Grooming is an innate behaviour represented across most animal species. It is a rich source of behavioural and biological information and forms an important part of the rodent behavioural repertoire. Mice show strain differences in their behavioural phenotypes, particularly in grooming behaviour. Various stressors and genetic manipulations alter mouse grooming. Kalueff & Tuohimaa (2005) defined behavioural differences and organisation in spontaneous grooming activity (novelty-induced) between three strains (129S1, NMRI, BALB/c) of laboratory mice. All three strains showed contrasting grooming phenotypes. 129S1 showed lower grooming activity and impaired microstructure, accompanied by lower vertical exploration. BALB/c and NMRI mice showed higher vertical activity and unimpaired grooming microstructure, and BALB/c mice showed higher grooming levels. Kalueff & Tuohimaa's (2005) study suggests that contrasting grooming phenotypes may not be due to strain differences in their sensory abilities, general activity levels, brain anatomy or aggressiveness, but rather reflects a complex interplay between anxiety, motor and displacement activity in these strains. They suggest that an in-depth ethological analysis of mouse grooming may be a useful tool in neurobehavioural research and could contribute to our understanding of behavioural disorders in humans.

Summary: Dingemanse et al. (2007)

Animal populations show individual differences in suites of correlated behaviours ("temperament", "animal personality") across different contexts ("behavioural syndromes"). Population variation in behavioural syndrome may exist for two reasons: 1) natural selection favours covariance in a trait and syndromes will evolve in response ("adaptive hypothesis"); and 2) stochastic processes (e.g. mutation, drift, founder effects, gene flow) maintain variation. Dingemanse et al. (2007) examined the adaptive hypothesis using a comparative approach. They measured 5 different behaviours (categories: aggression, general activity, exploration-avoidance-novel foods, novel or altered environments) across 12 different populations (6 predator-sympatric, 6 predator-naive) of three-spined stickleback (Gasterosteus aculeatus) and assessed whether the differences in behaviour varied consistently depending on the environment. Their results confirm the prediction of the adaptive hypothesis. They found that behavioural syndromes are not always the same in different types of population, implying that population variation in behavioural syndromes is not a result of stochastic evolutionary processes. They suggest that, in sticklebacks, behavioural syndromes are correlated with the presence of predators. Dingemanse et al. (2007) suggest that behavioural syndromes are not fixed according to physiological or genetic constraints and arise from adaptive evolution, where a behaviour is favoured because it is the most optimal trait in that environment.