Author confuses units from step 1 to step 2 of his arguments.<p>Step 1 starts with an &quot;S&quot; shaped graph of GDP&#x2F;Capita. Step 2 shows derivative of the curve, but is labeled as dGDP&#x2F;dt, ignoring dCapita&#x2F;dt. Author does not consider historical changes in demographics when GDP growth slows.<p>See demographic changes in Japan, Europe, US for examples of how population growth rates change due to economic and war-related shocks. Also see motivation for China ending the 1 child policy - they want to bring the cost of labor back down and they need a higher pop growth rate to generate enough economic activity to pay pensions, retirement, healthcare for expensive retirement-age cohort where people are living longer and thus costing the country much more.<p>Author should have challenged Porter&#x27;s initial claim: &quot;Anyone who believes exponential growth can go on forever in a finite world is either a madman or an economist.&quot;<p>While it makes for a good soundbyte, it ignores the symbiotic and (usually) directly proportional but lagged&#x2F;leading relationship of economic growth and population growth.