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I arrived at the same idea independently, anyhow, and published it in Social Science Information in 1989. To date it is my only publication in a refereed journal, and remains uncited as far as I know. Alan Rogers, a biologist at University of Utah, published almost the same idea in 1994! and 19972. Neither of us knew of Petty or Cassel or each other. Both of Rogers’ two papers are included in my appendix. Petty’s great idea has otherwise remained unnoticed as far as | know. His idea in modern terms comes from the same ancient capitalization formula. Sumerian temples knew how to evaluate land as well as mortgages and annuities by discounting to present value. In the simplest case, where cash flow is expected to hold constant forever, the logic begins with the definition cash flow cash flow rate = ————— capital Algebra allows h fl capital = |, (7.1) cash flow rate Years purchase, given those simplifying assumptions, meant 1 years purchase =——__———_ , (7.2) cash flow rate 1 The Evolution of Time Preference. 2 Evolution and Human Choice over Time. Chapter 7 Petty’s Idea 2/3/16 17 HOUSE_OVERSIGHT_011076