The domestication syndrome refers to a set of traits that are the by-products of artificial selection for increased tolerance toward humans [1, 2, 3]. One hypothesis is that some species, like humans and bonobos, “self-domesticated" and have been under selection for that same suite of domesticated phenotypes [4, 5, 6, 7, 8]. However, the evidence for this has been largely circumstantial. Here, we provide evidence that, in marmoset monkeys, the size of a domestication phenotype—a white facial fur patch—is linked to their degree of affiliative vocal responding. During development, the amount of parental vocal feedback experienced influences the rate of growth of this facial white patch, and this suggests a mechanistic link between the two phenotypes, possibly via neural crest cells. Our study provides evidence for links between vocal behavior and the development of morphological phenotypes associated with domestication in a nonhuman primate.