Family tree: "Aggression, like charity, begins at home."

Genealogists tell us that many U.S. presidents are related to each other through descent from King Edward III, a father of nine and ancestor of Washington, Jefferson, both Adamses, and both Roosevelts, plus Robert E. Lee, Charles Darwin and—here’s the come-down—80 percent of the present population of England. What fun is that?

As science writer Matt Crenson points out, the odds are that virtually everyone on earth has royal roots if you go back far enough (AP, July 1).

Crenson was moved to make these observations by the case of actress Brooke Shields. Genealogists had traced Shields’s ancestry and decided that she was related to Machiavelli, Hernán Cortés, Catherine de Medici, Lucretia Borgia, Charlemagne, El Cid, William the Conqueror, King Harold, five popes and the royal houses of virtually every European country. But as Crenson observed, that’s nothing special. It’s just a case of simple math: the longer ago a person lived, the more descendants that person is likely to have today.

The math does not always go in one direction. I can point to one lineage so exclusive that it is shared by at most one person. I think of that family tree when I look across the street at a big yellow Victorian house. There, on July 19, 1904, was born “Bud” or “Buddy” Robert Todd Lincoln Beckwith, the great-grandson of Abraham Lincoln. He never came back to see the childhood home in Riverside from which his divorced mother, Jesse Harlan Lincoln Beckwith, spirited him in 1907.

Her lively marital career began with her elopement in 1897. She left Riverside and her husband in 1907, married again in 1915, divorced again in 1925 and remarried in 1926.

Of her two children only Bud married, and he alone had the potential of continuing the Lincoln line. Bud was maritally adventurous too, but not in a way to keep the line going. This self-described “spoiled brat” and “gentleman farmer of independent means” had a vasectomy in 1962 before his third marriage, to Annemarie Hoffman, in 1968. Six months after the wedding he found out that she was pregnant. Bud’s urologist certified that he was sterile and could not be the father. Bud paid Annemarie off so she would list the baby’s father as unknown, but she broke the covenant and listed him as a Lincoln. A court in 1976 ruled that her boy, Timothy, was “the product of an adulterous relationship.” A trust fund was established in his name, worth $10 million to him if he could prove that he was a Lincoln.

Back to the nonexclusive pedigrees: Crenson cites a Dublin genealogist, Mark Humphrys, who estimates that Muhammad, the founder of Islam, “appears on the family tree of every person in the Western world.” Humphrys engages in a couple of speculative moves to arrive at that judgment, but let’s suppose it is true. Will anti-Muslims regard things differently if and when they realize that they are blood kin of the prophet? Would Franklin Graham have a more generous view of Muslims if he had an Uncle Muhammad?

Not likely. Family feuds, which is what we Jewish, Christian and Muslim children of Abraham are involved in, are the ugliest. Bronislaw Malinowski writes: “Aggression, like charity, begins at home.”

Still, it might throw a somewhat different light on current conflicts if we non-Muslims could see Muhammad as kin, and if Muslims could find shade under the branches of the tree of Edward III. The one thing nobody can claim is to be descended from Abraham Lincoln.