Reproduction upside down: The marsupial alternative

Abstract

Marsupials and eutherians diverged about 140 million years ago, and each developed a differing mode of reproduction. Current sequencing of the genome of two marsupial species, and now a monotreme, the platypus, will tell us much about the way in which these other mammalian lineages evolved their separate, but equally successful alternative reproductive strategies. Marsupial young are born at a very early stage of development and complete their growth in a pouch, or marsupium. They produce the smallest young, have the longest sperm, the longest period of embryonic diapause, the shortest pregnancy, become sexually differentiated after birth, and have the most sophisticated lactation of any mam..