Complex sentence: There was then a feud between Bateson and Pearson over the hereditary mechanism, solved by Fisher in his work "The Correlation Between Relatives on the Supposition of Mendelian Inheritance".
Split into simpler sentences: There was then a feud between Bateson and Pearson over the hereditary mechanism. Fisher solved this in "The Correlation Between Relatives on the Supposition of Mendelian Inheritance".