Chemistry has given the world the incredible diversity of fuels, pharmaceuticals, and household products that we rely on every day, along with tremendous advances in fighting infectious diseases and ensuring an abundant food supply. But the products of chemistry also include tens of thousands of toxic compounds that compromise human health, degrade the environment, and drive species to extinction. The advent of the modern environmental movement in the 1960s and 1970s produced a new field of chemistry dedicated to providing for the needs of society with less toxic and less environmentally damaging alternatives. This intellectual endeavor coalesced into the field of green chemistry. My guest, Terry Collins, is a leading green chemist and one of the founders of the field. His education includes a bachelor of science in 1974 and a PhD in 1978, both from the University of Auckland in New Zealand. He held a faculty position at the California Institute of Technology in the 1980s before joining the faculty at Carnegie Mellon University in 1988, where he is now the Director of the Institute for Green Science and the Teresa Heinz Professor of Green Chemistry. Terry is the recipient of numerous awards, including the Presidential Green Chemistry Challenge Award in 1998 and the Heinz Award for the Environment in 2010. He is also a Fellow of the American Chemical Society.

Rachel Carson alerted the world to the dangers of pollution with the publication of her book Silent Spring in 1962, and in the process, she helped to launch the environmental movement. My guest, Paul Ehrlich, alerted the world to the dangers of human population growth and resource consumption with the publication of his book The Population Bomb in 1968, and in the process, he accelerated the environmental movement. He has played a major role in that movement ever since, authoring dozens of influential books and many more articles. Ehrlich received a bachelor’s degree from the University of Pennsylvania in 1953 and a PhD from the University of Kansas in 1957. He has been a professor at Stanford University since 1959, where he is the president of the Center for Conservation Biology. He is the recipient of numerous environmental prizes, such as a MacArthur Fellowship, the John Muir Award of the Sierra Club, the Tyler Prize for Environmental Achievement, the Blue Planet Prize, and the Eminent Ecologist Award of the Ecological Society of America. Ehrlich is a fellow of the American Association for the Advancement of Science, the American Academy of Arts and Sciences, and the American Philosophical Society; he is also a member of the US National Academy of Sciences.

Global biodiversity is in the midst of a mass extinction driven by rapid human population growth and over-consumption of resources. These forces drive habitat loss, pollution, invasive species, climate change, and the many other proximate causes of species losses. The study of these forces, and how they can be mitigated to preserve biodiversity, is the responsibility of scientists engaged in the field of conservation biology. My guest, Thomas Lovejoy, is a founding scientist of this field, and often referred to as the Godfather of Biodiversity. Tom received B.S. and Ph.D. degrees in biology at Yale. He then held many prominent positions related to conservation, including with the World Wildlife Fund, the Smithsonian Institution, the World Bank, and the Inter-American Development Bank. He served in many scientific advisory roles for the U.S. government, and as a Conservation Fellow and Explorer at Large for National Geographic. Tom is a professor in the Environmental Science and Policy department at George Mason University and a senior fellow at the United Nations Foundation. He is the recipient of numerous environmental awards, including the Tyler Prize for Environmental Achievement and the Blue Planet Prize. He is also a Fellow of the American Association for the Advancement of Science, the American Academy of Arts and Sciences, the American Philosophical Society, the Linnean Society of London, and the American Ornithologists’ Union.

Nothing is more human than language, and no one has done more to advance the science of linguistics than Noam Chomsky. Noam was born in 1928, and completed undergraduate and graduate degrees at the University of Pennsylvania just after the Second World War. He earned his PhD in 1955, and by 1957, he was already publishing landmark works in linguistics that disrupted the field and fundamentally altered the understanding of language. His work also devastated the field of behaviorism, led by the likes of B.F. Skinner. Noam is known as the father of modern linguistics, but his influence extends well beyond the study of language to include fundamental applications in computer science, philosophy, cognitive science, and many other fields. Noam has taught at MIT since 1955, and at the University of Arizona since 2017.

Space exploration thrills kids and adults alike. Today I discuss the history of NASA and space science with Pam Melroy. Pam piloted the Space Shuttle missions STS-92 in 2000 and STS-112 in 2002, and she commanded STS-120 in 2007. We discuss the Mercury, Gemini, Apollo and Apollo-Soyuz programs, the Mariner 9 mission, Landsat satellites, Skylab, the Space shuttle, and the International Space Station. We also discuss scientific advances achieved in space in telemedicine, microgravity and health, protein crystal growth and drug development, and materials science, as well as the future of space science.

Freshwater ecosystems and their resident species have declined more rapidly than either terrestrial or marine systems and their species. Freshwater ecosystems face myriad stressors, from habitat loss and pollution to dams and climate change. Today I discuss the state of freshwater conservation science with Ian Harrison. Ian obtained his Ph.D. in systematic ichthyology at the University of Bristol in the UK. He has conducted research on marine and freshwater fishes in Europe, Central and South America, Africa, the Philippines, and the Central Pacific. He has worked for Conservation International and the IUCN’s Global Species Programme since 2008 and he is currently the freshwater specialist for Conservation International’s Moore Center for Science. Ian publishes extensively on the biology and conservation of fishes and the conservation of freshwater ecosystems.

Due to recent technological advances, scientists have revolutionized our understanding of human evolutionary history. What appeared to be a relatively simple story of divergence from ancient hominids is instead a tangled mess involving repeated cycles of divergence and hybridization between evolving human species. Today my guest is Jason Wilder, who researches human evolutionary genetics and genomics. We discuss the genetics of malaria resistance and parallel evolution, CCR5 deficiency and resistance to HIV infection, gene editing and the creation of designer babies, gene editing to treat disease, and introgression between modern humans and archaic forms, including Neanderthals and Denisovans. Jason received his B.A. in biology at Williams College and his Ph.D. in Ecology and Evolutionary Biology at Princeton University. He then worked at the University of Arizona and Williams before joining the faculty at Northern Arizona University, where he is a professor of genetics and the Interim Dean of the College of the Environment, Forestry and Natural Sciences.

The brain is the most enigmatic of organs – it is really a collection of organs that undergoes a remarkable coordinated development that is driven in part by sex steroids. Today my guest is Margaret McCarthy, one of the leading researchers on sex differences in the brain. Here, we cover the history of research on sex and the brain, including the utility of animal models, the roles of hormones and sensitive periods in brain development, masculinization vs. feminization of the brain, epigenetic regulation of sex differences in the brain, differences between the sexes in the prevalence and age of onset of mental illnesses, and even the role of politics in the field of neurobiology. Margaret received her BS and MA degrees in biology at the University of Missouri in 1981 and 1984, respectively, and her PhD in behavioral neuroscience at Rutgers University in 1989. She then worked at Rockefeller University and the National Institutes of Health before joining the faculty at the University of Maryland, where she holds an endowed professorship and is the Chair of the Department of Pharmacology.

Today we explore the history of plutonium with Frank von Hippel, a retired but always active professor at Princeton University, where, in 1975, he co-founded Princeton’s Program on Science and Global Security in the Woodrow Wilson School of Public and International Affairs. In the 1980s, Frank was the chairman of the Federation of American Scientists, and in the Clinton Administration he was the Assistant Director for National Security in the White House Office of Science and Technology Policy. Frank has worked on nuclear arms control and nonproliferation since the 1980s, and received many awards for this work, including a MacArthur Fellowship. Frank received his B.S. in physics at MIT in 1959 and his Ph.D. in theoretical physics at the University of Oxford in 1962, where he was a Rhodes Scholar. Frank is also a co-author of the forthcoming book, “Plutonium: How nuclear power’s dream fuel became a nightmare.” We discuss the history of all things nuclear – the development of the bomb, the attacks on Hiroshima and Nagasaki, plutonium bomb accidents during the Cold War, breeder reactors, radioactive waste, trans-uranic elements and neutron capture, nuclear terrorism and dirty bombs, nuclear testing, nuclear energy, and the people involved.

We explore the history of the discovery of gravitational waves with Rai Weiss, including the relevance to special and general relativity, pulsars, supernovae, merging and binary black holes, space and time, neutron star collisions, dark matter, cosmic background radiation, gamma ray bursts, and even the viscosity of neutrinos. We also discuss really small numbers, the origin of the NSF and NASA, the LIGO scientific collaboration, the politics of science, and what all this has to do with Albert Einstein. Rai received his PhD at MIT in 1962, and taught at Tufts University and Princeton before returning to MIT. Among Rai’s many distinguished awards is the 2017 Nobel Prize in Physics, which he received along with Kip Thorne and Barry Barish “for decisive contributions to the LIGO detector and the observation of gravitational waves.”