>>512921310 (OP)
Humans, and conversely organic sentient beings are cancer. I'm not joking
Cancer is something that happens where the metabolism in your body fails and it starts to develop chaotically out of order, as cancerous cells enter the bloodstream and move around to other parts of your body, eventually killing you from a lack of room for it.
Humans have conquered every landmass on the planet, and are trying to leave it, and we overall tend to grow, but declining birthrates could be a sign of the Earth moderating us in its ecosystem, or maybe a case-study in how cancer sometimes dies on its own.
Think about it. We are literally cancer, and the Earth is sick with it.