When I was a kid the world’s population was 3 billion, and today’s nearly 8 billion would have seemed the very definition of dystopia. And indeed, high population is to blame for a good fraction of climate change and other problems besides, though it has become unfashionable to speak of population as a problem.
Over these decades, the average weight of a human being has surely increased by 1/8. We’re larger than we were, and we eat more food and need more space and more materials. From the 1960s point of view, from the biomass and bioneeds points of view, it’s as if yet another extra billion had been added.
Looking around on the web, I find a 2012 paper by Sarah Catherine Walpole et al. that gives estimates of around half a billion.
[16 December 2020]