Male pregnancy is the incubation of one or more embryos or fetuses by male members of any species. In nearly all heterogamous animal species, offspring are ordinarily carried by the female until birth, but in fish of the Syngnathidae family (pipefish and seahorses), males perform this function. There are different ideas concerning whether a human male could become pregnant, and, by some definitions of gender identity, human men have become pregnant. Male humans incubating fetuses are also a recurring theme in speculative fiction.