Fig. 1.

Oxytocin nucleotide and amino acid sequences observed in primates, with the OXTR positions coevolving with OXT. The maximum likelihood phylogenetic tree was based on an ∼8-Mb genomic sequence reported by Perelman and colleagues (19). Nonsynonymous nucleotide and amino acid changes are shown in red. Taxonomic families and subfamilies are indicated, as well as species with common male care (in bold) and those with twin pregnancies (asterisks). The trace (−) indicates that no information is available.