Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent every weekday. Email address Sign up Thank you! Terms of Service and Privacy Policy. An organism’s fecundity is the number of offspring it can have in a lifetime. Here, species are listed from left to right by adult body weight. This article originally appeared in the December 2013 issue of Popular Science. More deals, reviews, and buying guides The PopSci team has tested hundreds of products and spent thousands of hours trying to find the best gear and gadgets you can buy. SEE MORE GEAR