With some accounts estimating fewer than 2,800 individuals left, the blue-eyed black lemur of Madagascar is one of the most threatened primates in the world. Reports suggest that one of the remaining populations of blue-eyed black lemurs has begun to mate with neighboring black lemurs. This interaction could contribute to the extinction of one or both lemur species. Understanding why this interaction is happening, and what it means for species survival, is essential for their conservation.