It may be possible to confirm family relationships with Howland by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
Y-chromosome DNA test-takers in his direct paternal line on WikiTree:
Dave Soule :
Family Tree DNA Y-DNA Test 37 markers, haplogroup I-YSC0000261, Ysearch UUAXF, FTDNA kit #428396 +
AncestryDNA Paternal Lineage (discontinued) 37 markers, haplogroup I-M253, Ysearch UUAXF