RT Journal Article SR Electronic T1 Ratcheting the evolution of multicellularity JF Science JO Science FD American Association for the Advancement of Science SP 426 OP 427 DO 10.1126/science.1262053 VO 346 IS 6208 A1 Libby, Eric A1 Ratcliff, William C. YR 2014 UL http://science.sciencemag.org/content/346/6208/426.abstract AB