The two homes highlight the prominent roles that Lincoln and Darwin proudly and passionately shared: as husbands, fathers, householders. In the parlance of their era, both men qualified as "gentlemen" – Darwin by birth and breeding, Lincoln through his own relentless and self-conscious effort. While Darwin compiled a glittering record at Cambridge, Lincoln made up for his own lack of formal education by driving his oldest boy, Robert, to academic excellence. When Robert failed his Harvard entrance exams in 1859, the Lincolns enrolled him at Phillips Exeter Academy in distant New Hampshire, until he won admittance to Harvard on his second try (and graduated before entering the Union Army in 1864).

Both Lincoln and Darwin adored their children, and mourned prodigiously over the early, tragic death of Annie Darwin (aged ten, in 1851), Eddie Lincoln (age four, in 1850), and Willie Lincoln (age eleven, in 1862, at the height of the Civil War). Both men relished spending time in family pursuits at home. Lincoln enjoyed reading aloud to his boys, or wrestling with them on the floor -- though his career as a circuit-riding lawyer and ceaselessly ambitious politician kept him frequently on the road. Describing the carefully reconstructed ground floor of Down House, the curators explain: "Here you imagine Darwin, the man and father, scooting about his study in his wheeled armchair, taking on his sons at billiards and sprawling on the blue couch in the drawing room while Emma plays her grand piano (with 'vigour and spirit, but not passion,' recalled their daughter Henrietta)."

Both men, despite bouts of anxiety and "melancholy" (to use a phrase in vogue at the time) took great care to live up to expectations in their conventional, respectable, honorable roles as family patriarchs. Other bearded eminences of the era showed well-advertised contempt for middle class mores – as did Lincoln's worshipful poetic supporter, Walt Whitman, or Darwin's fan Karl Marx (who sent the naturalist an inscribed copy of the first volume of "Das Kapital," signed "from his sincere admirer.")

In the last analysis, rebels and free spirits could dismiss Abe and Charles as hopelessly bourgeois—timid souls who whole-heartedly embraced the proper joys of family life so frequently celebrated in the Victorian age. Though married relatively late in life (Darwin at 29, Lincoln at 33), both men ultimately seized the opportunity wittily described by their contemporary W.S. Gilbert: "to indulge in the felicity/ of unbounded domesticity." Yes, Lincolns and Darwins suffered their share of tragedies– the sort of losses melodically mourned in the sentimental songs that Honest Abe immoderately loved –but these setbacks in no way compromised the commitment of the two heads of household to ideals of family bliss.

In commemorating the dual bicentennial of February, 2009, this crucial, unshakable and enthusiastically shared attitude on the part of the martyred president and the world-shaking scientist managed to escape serious notice from leading commentators. It's too bad, since few interested individuals can hope to replicate the genius or stature of the two birthday boys, but we can each aspire to their favored function as devoted fathers, good neighbors, and proud heads of household in comfortable and respectable middle class homes.