Adult female cercopithecines have long been known to bias their social behaviour towards close maternal kin. However, much less is understood about the behaviour of paternal kin, especially in wild populations. Here, we show that wild adult female baboons bias their affiliative behaviour towards their adult paternal half-sisters in the same manner and to the same extent that they bias their behaviour towards adult maternal half-sisters. Females appear to rely heavily on social familiarity as a means of biasing their behaviour towards paternal half-sisters, but may use phenotype matching as well.

Twenty-nine human microsatellite primer pairs were screened for their utility in the cross-species amplification of baboon DNA derived from both blood and feces as part of a larger study to identify paternal half sisters in a population of wild baboons (Papio cynocephalus). Forty-one percent (12/29) of the human primers successfully amplified baboon DNA. Of these 12 primers, six amplified fragments that were both polymorphic and heterozygous (mean number of alleles = 6, mean heterozygosity = 87%) and yielded repeatable results. However, only five of these six simple tandem repeat polymorphisms (STRPs) showed patterns of Mendelian inheritance (i.e., mothers and offspring shared at least one allele at each locus), and were therefore useful for determining relatedness between individuals. Analysis of the sixth primer revealed non-Mendelian inheritance, i.e., three of the six known mother-daughter pairs had no shared alleles. This failure was probably due to non-specific fragment amplification, and may have resulted from a different STRP locus being amplified in mother and daughter. This finding highlights the importance of sampling DNA from known parent-offspring pairs when screening microsatellite primers for genetic studies. Multiple, independent replications of genotypes and Mendelian checks are both particularly important when using crossspecies amplification or when using a low-quality source of DNA.

Cole Skinner was hanging from a wall above an abandoned quarry when he heard a car pull up. He and his friends bolted, racing along a narrow path on the quarry's edge and hopping over a barbed-wire fence to exit the grounds.The chase is part of the fun for Skinner and his friend Alex McCallum-Toppin, both 15 and pupils at a school in Faringdon, UK. The two say that they seek out places such as construction sites and disused buildings -not to get into trouble, but to explore. There are also bragging rights to be earned. "It's just something you can say: 'Yeah, I've been in an abandoned quarry', " says McCallum-Toppin. "You can talk about it with your friends. "Science has often looked at risk-taking among adolescents as a monolithic problem for parents and the public to manage or endure. When Eva Telzer, a neuroscientist at the University of North Carolina in Chapel Hill, asks family, friends, undergraduates or researchers in related fields about their perception of teenagers, "there's almost never anything positive", she says. "It's a pervasive stereotype. " But how Alex and Cole dabble with risk -considering its social value alongside other pros and cons -is in keeping with a more complex picture emerging from neuroscience. Adolescent behaviour goes beyond impetuous rebellion or uncontrollable hormones, says Adriana Galván, a neuroscientist at the University of California, Los Angeles. "How we define risk-taking is going through a shift. "Adolescents do take more risks than adults, and the consequences can include injury, death, run-ins with the law and even long-term health problems. But lab studies in the past decade have revealed layers of nuance in how young people assess risks. In some situations, teenagers can be more risk-averse than their older peers. And they navigate a broader range of risks than has typically been considered in the lab, including social risks and positive risks -such as trying out for a sports team. These types of behaviour seem to have different effects on the brain.How adolescents interact with risk is important. Work on the neural underpinnings of risky behaviour can inform guidelines and laws for

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