 Finally, historical contingency is a counterfactual notion, and although this issue has not gotten as much attention as it deserves, there is a nascent philosophical literature on historical counterfactuals (Tucker 2004: 227ff; Nolan 2013; Radick 2016; Zhao 2017 in Other Internet Resources). The debate about historical contingency can be construed as a disagreement about the truth of various historical counterfactuals. Gould claimed that if things in the Cambrian had been slightly different, there would be no vertebrates today, let alone humans, while other convergentists claim that humanlike cognitive abilities, language, tool use, and sociality would have evolved even if other things had been different in the past—for example, if the non-avian dinosaurs had not gone extinct.