Also in Silver Age and Modern continuity Kryptonians have more than one ethnic group, such as dark-skinned Kryptonians from Krypton's Vathlo Island that resembles Earth humans of Sub-Saharan African descent, and a group from the continent of Twenx that resembles Earth Asian and Latino peoples.
"Man of Steel, Woman of Kleenex" is a 1971 essay in which science fiction author Larry Niven details the problems that Superman would face in sexual intercourse and reproducing with "a human woman designated LL for convenience," using arguments based on humorous reconciliation between physics, biology, and the abilities of Kryptonians as presented in Superman comic books.