Once our population started growing following the agricultural revolution , we would have quickly outstripped fairies in terms of weight. In 2015, fairy biomass would be down to about 1.2% of human biomass, and by the mid-21st-century, they'd bottom out at less than 1%. But as long as humans keep reproducing, the fairy population would keep growing. If we assume the human population will level off at around 9 billion partway through this century, then the share of mass occupied by fairies would continue rising steadily. If our population stays at a stable 9 billion indefinitely, by 2100, they'll be back above 1% of human biomass, and they'll reach 2% by the year 3000. In the year 100,000, if our species is somehow still around, they'll outweigh us. This makes things interesting. Let's assume fairies need to eat. If fairies weigh about as much as us, they'd presumably be consuming a similar share of food and water. So even if the Earth can support 400 m...