The biggest natural constraint was nitrogen fixation which places a natural limit of around 4 billion people. But artificial fertilizers basically took the lid

The biggest natural constraint was nitrogen fixation which places a natural limit of around 4 billion people. But artificial fertilizers basically took the lid of that and the population has been exploding since been the process was first industrialized. https://pdfs.semanticscholar.org/9ef1/254c1b7626ae1c70f0718c0f811d11d990da.pdf https://pdfs.semanticscholar.org/9ef1/254c1b7626ae1c70f0718c...