For some time after the big bang there were no stars. Researchers are now looking at cosmic dawn—the time when stars first popped into being—and are seeing hints of dark matter’s influence on supercold hydrogen clouds. News Writer Adrian Cho talks with Sarah Crespi about how this observation was made and what it means for our understanding of dark matter. Sarah also interviews Joanna Kaplanis of the Wellcome Sanger Institute in Hinxton, U.K., about constructing enormous family trees based on an online social genealogy platform. What can we learn from the biggest family tree ever built—with 13 million members spanning 11 generations? In a bonus segment recording during a live podcasting event at the AAAS Annual Meeting in Austin, Sarah talks with Michael Varnum of Arizona State University in Tempe about what people think they will do if humanity comes into contact with aliens that just happen to be microbes. Live recordings sessions at the AAAS meeting were supported by funds from the European Commission. This week’s episode was edited by Podigy. Listen to previous podcasts. [Image: Kilo-Degree Survey Collaboration/H. Hildebrandt & B. Giblin/ESO; Music: Jeffrey Cook] Learn more about your ad choices. Visit megaphone.fm/adchoices

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“What did the council decide on item 42?” — answered with the speaker and the moment.

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