All else equal, a species would rather have a smaller global population when starting to use fossil fuels. There's only so much capacity for use of fossil fuels

All else equal, a species would rather have a smaller global population when starting to use fossil fuels. There's only so much capacity for use of fossil fuels, and more people means less per-capita. Before we used fossil fuels, 100% of economic growth was funneled into population growth. That trend was only bucked with the industrial revolution with its associated fossil fuel use.