No one can tell you for sure what the appendix does. No one knows how deep into the Earth life goes. No one knows how high into the sky life goes. No one is sure what the mites that live on human foreheads do, though they are there while you are reading.
Most species on Earth remain unnamed, not to mention totally unstudied. New species are easy to find in Manhattan, walking around alongside celebrities. No one can tell me what the species of bacteria living on my body, hundreds of species, are doing. No one can say for sure if there is another, yet to be discovered, domain of life. Parasites in my body might be affecting my behavior, and even the sorts of things I write late at night.
There are ant species that farm fungus in the Amazon. There are beetle species that farm fungus in my backyard. Both do so with greater sophistication than I or any other human can farm fungus. No one is sure why weaver ants have green abdomens. No one knows why we have specialized glands in our armpits that feed bacteria that produce the smells we think of as body odor. No one is sure why we have such large sinuses. There exists active discussion about why our bodies are warm and not cold.
There is a bacteria species that lives in hot water heaters, but nowhere else yet studied on Earth. Hummingbirds can bend their beaks in the middle using muscles in their head, but no one has checked to see whether other birds can do the same thing. Most mice on Earth might be singing, but only a few have been listened to.
I like to do and write about biology for these reasons, because in biology most of what is knowable is still unknown, because in biology we are still ignorant, because in biology the very body I use to type these words, with its crooked fingers and twisty mind, is only partially, modestly, understood, because biology will never fully be understood, because biology is a tapestry being unraveled, because the lives of the people unraveling the stories are, even when superficially humble and human, always fascinating, because biology is like biography with better characters, because I find deep and wondrous joy in biology, because even when an editor writes me late at night to ask why I write about and do biology my first response is to smile at how much I love biology, smile and wonder, the way we all wonder before the grandeur of the stars but sometimes forget to wonder before the grandeur of life.