"All of us are part of an old, old family," begins Peters's (Cold Little Duck, Duck, Duck) lyrical, child-friendly book about evolution. Stressing the kinship of humans with all living things, the text identifies each of the species at various stages of evolution not just as "our" relatives but as ourselves ("We didn't have two eyes to blink or ten toes to wiggle. We were just tiny round cells in the deep, dark sea"). Focusing briefly on selected successive stages over millions of years, her descriptions emphasize the "outside" and "inside" of each creature ("On the outside, we were squishy and soft, like worms. On the inside, our cells had many shapes—square like boxes, pointy like stars, round like ripe seeds"). While most of the writing seems keenly attuned to young readers, there is one troublesome exception. The pivotal concept—that all life shares a common ancestor—is introduced as Peters writes that the cells in the deep, dark sea "had the same kind of spiraling genetic code for life we have today"; the idea of a genetic code goes unexplained, even in the endnotes. Stringer's (Scarecrow) warm, inviting acrylics alternate full-bleed vistas with close-ups of each stop on the journey, effectively mirroring the text's outside/inside approach. An arresting image of a fish, for instance, in shades of cobalt and sea green, is flip-flopped on the opposite page as a tawny fossil. An illustrated timeline helps readers place the information in context. All ages. (Apr.)