Simple animals like jellyfish and hydra, even roundworms, sleep. Without brains. Why do they sleep? How can we tell a jellyfish is sleeping? 

Staff Writer Liz Pennisi joins host Sarah Crespi to talk about what can be learned about sleep from these simple sleepers. The feature is part of a special issue on sleep this week in Science.

Next is a look at centuries of alien invasions—or rather, invasive insects moving from place to place as humans trade across continents. Sarah talks with Matthew MacLachlan, a research economist at the U.S. Department of Agriculture’s Economic Research Service, about his Science Advances paper on why insect invasions don’t always increase when trade does.

Finally, a book on racism and the search algorithms. Books host Angela Saini for our series of interviews on race and science talks with Safiya Umoja Noble, a professor in the African American Studies and Information Studies departments at the University of California, Los Angeles, about her book: Algorithms of Oppression: How Search Engines Reinforce Racism.