Where do new species come from? Darwin proposed that the diversity of life could be explained when population divisions become magnified into new species over time. This “tree of life” thinking became our foundational metaphor for the natural world. Hybridization –– mating between species –– undercuts “tree thinking.” Until recently, this phenomenon was regarded as an evolutionary dead end and ignored. However, new data from diverse fields point to an inescapable conclusion: hybridization is common and can significantly impact living things (including our species!). So, we will celebrate Darwin’s birthday by asking whether Darwin’s tree still adequately represents life’s diversity or if a new metaphor is needed.