Episode Summary
Executive Summary: The episode pairs two evidence-based conversations about human impacts on nature and on parenting. First, Walter Jetz explains why biodiversity loss is driven by multiple human pressures beyond climate change, with amphibians especially at risk. Then Emily Oster, joined by researcher Nikita Suit, weighs research on breastfeeding, sleep, safe sleep, co-sleeping, milk sharing, and sleep training, emphasizing nuance, safety, and where evidence is strong versus weak.
Main Topics: Global biodiversity crisis and extinction risk (Priority: 5/5): Walter Jetz discusses the UN biodiversity report’s estimate that up to one million species are threatened, stressing that extinction is caused by a “perfect storm” of deforestation, land/sea-use change, hunting, pollution, invasives, and climate change—not climate alone. Amphibians as an especially vulnerable group (Priority: 5/5): Jetz explains that frogs, toads, salamanders, and other amphibians are disproportionately threatened because they have narrow ranges, are sensitive to microclimate, and are hit by invasive species and habitat loss, making them strong indicators of ecosystem decline. Why biodiversity matters to people (Priority: 4/5): The conversation highlights ecosystem services and direct human benefits from biodiversity, including pollination, pest control, and potential medical compounds that may be lost before species are even discovered. Evidence-based parenting and the limits of mythology (Priority: 5/5): Emily Oster describes using data to answer common parenting questions, arguing that many widely held beliefs are weakly supported and that parents need clearer synthesis of the literature, not isolated studies. Breastfeeding, breastfeeding duration, and milk sharing (Priority: 5/5): Oster argues that the strongest evidence is for breastfeeding versus not breastfeeding, with benefits concentrated early in life, while extended breastfeeding shows limited additional evidence in U.S. contexts. Suit adds that informal breast-milk sharing is often unregulated and can pose contamination risks. Sleep, sleep training, and safe sleep (Priority: 4/5): The discussion covers swaddling, sleep training, and back-sleeping. Oster says sleep training can improve infant sleep and parental well-being without known long-term harm, while back-sleeping has strong evidence for reducing SIDS. Parenting beyond babies: discipline, grandparents, and mental health (Priority: 3/5): The panel notes that evidence is thinner for older children, but consistency in discipline matters. Oster also broadens the discussion to fathers, grandparents, and the mental health of all caregivers in the postpartum period.
Key Arguments: Human-driven extinction is not caused by climate change alone; land-use change, deforestation, hunting, pollution, and invasive species are major drivers. The estimate of one million threatened species is based on extrapolation from assessed groups and may be conservative because many insects and tropical species remain unstudied. Amphibians are at exceptional risk because of small geographic ranges and high sensitivity to environmental change and invasives. Biodiversity loss matters directly to humans through pollination, pest control, and potentially undiscovered medicines. The best breastfeeding evidence compares breastfeeding to no breastfeeding; benefits after the first year are much less clear in U.S. settings. Informal breast-milk sharing can be meaningful and compassionate, but without screening it can carry contamination and medication risks. Back-sleeping is strongly supported by evidence to reduce SIDS. Sleep training appears to improve sleep and parental outcomes without evidence of long-term harm, though methods vary. For younger children, consistency in discipline is more evidence-based than punitive improvisation. Evidence is weaker for older-child questions, which are often more individualized and less researchable.
Data Points: Species threatened with extinction: Up to 1 million - UN biodiversity report discussed by Walter Jetz Estimated total species on Earth used for report calculations: About 8 million - Base estimate used to extrapolate threatened species counts Formally assessed species to date: About 100,000 - Jetz describes how extinctions were extrapolated from assessed groups Amphibian species newly assessed as threatened or endangered: Over 1,000 - Current Biology study referenced in the interview Amphibian share of global species at risk: 40% - UN biodiversity report statistic for amphibians Coral share of global species at risk: 33% - UN biodiversity report statistic for corals Insect share of global species at risk: Around 10% - UN biodiversity report statistic, noted as conservative and based on limited assessments Vertebrate extinctions since medieval times: Over 800 - Jetz cites historical extinctions as evidence of rates far above background Extinction rate relative to background: Tens to hundreds times higher - Comparison to extinction rates over the last 10 million years Amphibian range size compared with birds: About 6 times smaller - Explains why habitat loss affects amphibians so strongly Breastfeeding benefits most clearly supported: Early-life benefits, especially the first year - Oster notes stronger evidence for reduced diarrhea, ear infections, and possibly allergies Infant sleep-through-night age: About 6 to 7 months - Oster’s response about sleep training expectations Colic age mentioned: Around 3 months - Parent question about colicky infant and elimination diets Milk-bacteria study result: 74% had gram-negative bacteria - 2013 Pediatrics study of milk bought through an online sharing site Formula cost: About 8 to 31 cents per ounce - Suit’s comparison of infant feeding costs Daily formula cost for a 3-month-old: Up to about $10/day - Based on ~30 ounces/day consumption Informal shared milk price: Up to $4 per ounce - Suit describes high-priced online milk sharing Daily cost of informal shared milk: About $120/day - Cost estimate for a 3-month-old consuming roughly 30 ounces/day Milk bank price: $3 to $5 per ounce - Suit explains regulated donor milk is costly because of screening/testing
Pivotal Quotes: "It’s a perfect storm of deforestation, changes in land and sea use, hunting and poaching, pollution, the introduction of invasive species." — Ira Flatow (introducing the UN report findings): Sets up the biodiversity discussion by emphasizing multiple human causes of species loss "The benefits seem to accrue mostly early on in life." — Emily Oster: Explains why evidence does not strongly support extended breastfeeding benefits in the U.S. "The evidence suggests that the recommendation for backsleeping has been really important for policy." — Emily Oster: Summarizes the research basis for safe-sleep guidance
Implications: Listeners are encouraged to treat both biodiversity and parenting advice through evidence, not assumptions. Conservation should target the most threatened species and places, while parents can make more informed, less guilt-driven choices about breastfeeding, sleep, and infant care.