Who would imagine that Johann Zoffany’s celebrated 1780 depiction of the extensive Sharp family happily making music on their pleasure barge could be parsed so deftly into a portrait of an age? Or that Hester Grant, embarking upon her research, could have foreseen how topical Granville Sharp’s determined champaign against slavery would seem at the present moment? Or that his surgeon brother William’s new-fangled passion for ‘variolation’ or vaccination (against smallpox in those days) should strike such a chord today? What a family, and what an age: the seven Sharp siblings not only helped refashion the 18th-century world around them,...