Breadth of expression and maximal expression is compared in three groups of observations: (1) autosomal paralogs of X-linked genes, (2) other autosomal paralogs matched by age, (3) X-linked paralogs. Newly formed paralogs are defined as those mapped by phylogenetic timing to taxa Theria or younger. Pre-existing duplications are defined as those descending from duplication notes mapped by phylogenetic timing to taxa Amniota or older.