What do you call a man who builds a wooden machine to think for him — and then decides the human brain was never anything more than that machine to begin with?

In January 1870, William Stanley Jevons carries his invention into Burlington House, nervous that the Royal Society will laugh him off the stage. They don't. The thing he's built — the Logical Piano, made of rods, levers and pulleys by a clockmaker in Salford — can draw logical conclusions on its own. And if a machine can think, Jevons starts to wonder, what exactly is the human brain doing differently?

What happens to free will once a man's actions are just the output of a calculation? Why does a philosopher gathered with friends at a Cambridge vicarage stand up and say the whole picture is built on sand? And why does Jevons, a free-market man to his bones, end up arguing for public libraries and schools for the poor?

Along the way: a football match that explains the entire theory of wages, a teenage diary entry from the slums of Spitalfields, and a phrase — "a pleasure-seeking machine" — that will outlive everyone in the room.

History of Economic Species tells the story of the evolution of its main character, Homo Economicus. This is the second half of chapter two.

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Music and audio

• "Good Times", "Blammo", "By Grace" and "Lode Runner" by Podington Bear, via Free Music Archive, licensed under Attribution-NonCommercial 3.0 Unported (CC BY-NC 3.0)
• "CronoCrono", "Hardboil", "Journalistic", "Simos Harbor" and "Vernouillet" by Blue Dot Sessions, licensed under Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)
• "Soul Skip" by Ketsa, via Free Music Archive, licensed under Attribution 4.0 International (CC BY)
• "Wildflowers" by Scott Buckley, licensed under a Creative Commons Attribution 4.0 International License

Voice over by Oliver Morrell, via Fiverr

Sources quoted in this episode

• Edgeworth, Francis Ysidro. Mathematical Psychics. 1881.
• Jevons, William Stanley. "On the Mechanical Performance of Logical Inference." Philosophical Transactions 160, 1870.
• Jevons, William Stanley. The Coal Question. 1865.
• Jevons, William Stanley. The Theory of Political Economy. 1871.
• Jevons, William Stanley. The State in Relation to Labour. 1882.
• Jevons, William Stanley. Letters and Journal of W. Stanley Jevons. 1886.
• Sidgwick, Henry. The Methods of Ethics. 1874.
• Henry Sidgwick: A Memoir. 1906.