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This Week in PNAS: Aug 2, 2016

In the early, online edition of the Proceedings of the National Academy of Sciences, researchers from the University of Alaska Fairbanks, Pennsylvania State University, and elsewhere look into when and how the woolly mammoth became extinct on St. Paul Island, Alaska, home to one of the mammoth populations that remained thousands of years after extinction on Alaska's mainland. Using several different approaches, including analyses of ancient DNA from soil sediment cores, the team found evidence that woolly mammoths persisted on the Beringian island up until roughly 5,600 years ago, following a period of dry climate and diminished freshwater availability. The group detected mammoth DNA in soil samples from nearly 11,000 years ago, but did not see it in samples restricted to the last 5,610 years.

A team from the University of Calgary and the University of Illinois attempts to tease apart human body form traits stemming from adaptive or non-adaptive processes. The researchers used evolutionary quantitative methods to estimate the direction and force of selection acting behind various body traits to try start teasing apart human body variations associated with adaptation, genetic drift, or gene flow. "Although most traits appear to be under directional selection, their response is constrained by between-trait covariance," they write. "This finding suggests that trait differences among human groups may not directly reflect the forces of selection that shaped them."

Finally, researchers from the UK report on findings from a study focused on unraveling relationships between chromatin state, histone modifiers, and gene expression at the Flowering Locus C (FLC) in the model plant Arabidopsis thaliana. In particular, the team focused on physical associations between an H3K36me3 methyltransferase enzyme called SDG8associated with active FLC transcription and an opposing histone modifier, the ELF6 demethylase, linked to an H3K27me3 form of histone and transcriptional silence. The study's authors note that SDG8 and ELF6  "influence the localization of each other on FLC chromatin, showing the functional importance of the interaction. In addition, both influenced accumulation of the associated H3K27me3 and H3K36me3 histone modifications at FLC."