The study of the evolution of mammalian pregnancy provides interesting insight into the genetic origins of evolutionary innovations. It can also identify genes that are promising targets for treatment of human reproductive diseases. We have developed an approach for detecting the counterparts of human genes in the genomes of 43 other species of vertebrates. We will use this approach to find genes that are associated with mammalian pregnancy by looking for genes that either appeared at the origins of placental mammals or which experienced strong evolutionary changes in that period. Moreover, because the cellular mechanism of placentation parallels metastasis, a better understanding of the evolution of placentation also has relevance to the study of cancer.