Who are our kin? Our siblings? Our parents? What about our ancestors? Or our pets? Could the earth, too, be kin? Sæbjörnsson considers our terrestrial evolutionary ancestors by breaking down the perennial, arboreal image of evolution, offering instead a complicated web of mutual reciprocity that reconsiders our intimate relationship with volcanoes, rocks, and lightning—and even the conditions that make these substances and events possible, like humor and love.