> Such data show us that important cultural developments in the fourth millennium B.C.E.—including the Yamnaya migration and the dissemination of kurgans and Indo-European culture—probably took place many centuries before the first horses were domesticated
I can't find the citations to this in the article.
The tone of the article seems like this author has a particular schtick with the Yamnaya and / or the Indo Europeans. A lot of academia and journalists do this so not surprised.