Why Do We Trust Strangers? A 5,000-Year Story in 11 Minutes

Today you'll probably eat food cooked by someone you've never met, get into a stranger's car, and type your card number into a website run by people you'll never see. For almost all of human history, that would have been insane. So why do we do it, and why does it usually work? In this video we follow trust from villages of 150 people to medieval merchants who ran a sea-wide trade on reputation, New York diamond dealers who still close deals with a handshake, 5,000-year-old clay seals, the first registered trade mark, eBay's first sale (a broken laser pointer), 17,000 "lost" wallets, and the $16 billion scam economy that exploits it all. This is part 2 of the series. Part 1: What Is Money? → [link] Chapters 0:00 Why do we trust strangers? 0:37 The 150 Problem 1:59 The Handshake Economy 3:45 Trust You Can See 5:21 The Stranger Machine 6:57 The Lost Wallet Test 8:28 The Trust Dividend 9:55 So… why do we trust strangers? What's the most trusting thing you've ever done with a stranger? Tell me in the comments. Sources The 150 Problem Hill & Dunbar (2003), Social network size in humans (Christmas cards): https://link.springer.com/article/10.... Dunbar & Sosis (2018), Optimising human community sizes (Hutterites): https://www.sciencedirect.com/science... Lindenfors et al. (2021), "Dunbar's number" deconstructed: https://royalsocietypublishing.org/do... Dunbar, Marriott & Duncan (1997), Human conversational behavior: https://link.springer.com/article/10.... Dunbar's "drink in a bar" definition: https://oxsci.org/end-of-dunbars-number/ The Handshake Economy Greif (1989), Reputation and Coalitions in Medieval Trade: Evidence on the Maghribi Traders: https://www.cambridge.org/core/journa... The scholarly debate about the Maghribi traders: https://web.stanford.edu/~avner/greif... Bernstein (1992), Opting Out of the Legal System: Extralegal Contractual Relations in the Diamond Industry: https://chicagounbound.uchicago.edu/j... Trust You Can See Britannica, Cylinder seal: https://www.britannica.com/art/cylind... The Met, sealed clay envelope for a merchant's letter (Kanesh, c. 1900 BC): https://www.metmuseum.org/art/collect... The Goldsmiths' Company Assay Office, History of hallmarking: https://www.assayofficelondon.co.uk/a... The first UK trade mark: the story of Bass & Co: https://www.barkerbrettell.co.uk/the-... The Stranger Machine eBay, Meet the buyer of the broken laser pointer: https://www.ebayinc.com/stories/news/... Pierre Omidyar's 1996 letter to eBay users: https://pages.ebay.com/services/forum... History.com, The rise and decline of hitchhiking: https://www.history.com/articles/hitc... Uber, Q4 and full-year 2025 results (40M+ trips a day): https://investor.uber.com/news-events... Airbnb, About us (2.5B+ guest arrivals): https://news.airbnb.com/about-us Knowledge at Wharton, The inside story of Airbnb: https://knowledge.wharton.upenn.edu/p... Abrahao et al. (2017), Reputation offsets trust judgments based on social biases among Airbnb users: https://www.pnas.org/doi/10.1073/pnas... The Lost Wallet Test Cohn et al. (2019), Civic honesty around the globe: https://www.science.org/doi/10.1126/s... PBS NOVA, Humans are surprisingly honest when it comes to returning lost wallets: https://www.pbs.org/wgbh/nova/article... Berg, Dickhaut & McCabe (1995), Trust, Reciprocity, and Social History: https://www.sciencedirect.com/science... The Trust Dividend Our World in Data, Trust (Arrow quote, World Values Survey): https://ourworldindata.org/trust Pew Research Center (2025), Americans' trust in one another: https://www.pewresearch.org/2025/05/0... FTC (2026), People reported losing $3.5 billion to imposter scams in 2025: https://www.ftc.gov/news-events/news/...