I'm researching proto-Indo-European, and have seen a few remarks which imply that an -es suffix for plural was a likely component of the language (including here on L.SE; Wiktionary). Is this a widespread academic belief? Is the suffix found in many Indo-European languages, other than (in a form) English?
Also, just to confirm: if this suffix is believed to be to descend, did it represent plurality or just duality?