Viviparity is so advantageous that it has evolved at least 140 times in the invertebrates, but some Australian and New Zealand onychophorans have gone back, abandoning ovoviviparity to return to eggs. Why? Here we propose that it is an adaptation to climatically inhospitable habitats and low food availability.

Keywords: evolution of reproductive modes, viviparity, ovoviviparity, velvet worms, climate and reproduction