A few books on presidential trivia have appeared recently. One listed each
president’s last words. A profound final presidential statement that struck me
was “I don’t like the wallpaper in this room.”
Considerable interest in the ancestor tables of presidents has developed in
the past few years (note the several articles on this subject in The American
Genealogist) and with the recent publication of Ancestors of American
Presidents (1989) by Gary Boyd Roberts, now in its first revised edition,
published in December 1989 by Carl Boyer 3rd of Santa Clarita, California. A
comparative study of the inbreeding of our presidents could be interesting,
since inbreeding is something we can calculate from these ancestor tables.
Briefly one measures inbreeding with an inbreeding coefficient, a
fraction which ranges from 0.0 (zero) to 1.0 (one). A person’s inbreeding
coefficient is a fraction which estimates the probability that he or she
received the same allele for a given gene through both parents, because the
allele was derived from their common ancestm. Put another way, an inbreeding
coefficient is that fraction of a person’s genes where identical contributions
have come from both parents because of their descent from a common
ancestor or ancestors. An inbreeding coefficient of 0 (zero) means that a
person is not inbred at all, and an inbreeding coefficient of 1 (one) means that
a person is completely inbred. But humans would rarely approach complete
inbreeding. No doubt the average inbreeding in the U.S. is well below the
0.00006 which would result from a sixth-cousin marriage. Examples of high
inbreeding in humans would be 0.25 from the union of a brother and sister or
from a parent and child.
Inbreeding, then, depends on the relationship of a person’s parents. So, if a
mother is inbred, but is not related to the father, there is then no
inbreeding in the child, and vice versa, because the parents are not
related. For example, President Kennedy’s mother Rose Elizabeth (Fitzgerald)
Kennedy was a child of a second-cousin marriage (D.K. Goodwin, The
Fitzgeralds and the Kennedys , pp. 88-89, 827). Mrs. Kennedy’s
inbreeding coefficient is 0.0156, but her son President Kennedy was not inbred
because we know of no relationship between his parents.
Of the presidents, from the published ancestries I have seen, President
Carter could be slightly inbred through a possible relationship of Eliza Pratt
(maternal 3rd-great-grandmother) to James Pratt (paternal
3rd-great-grandfather). If these Pratts were as close as brother and sister,
President Carter’s inbreeding coefficient would be 0.0009, produced from a union
of fourth cousins. According to Roberts (op. cit., p. 91), the parentage
of Eliza is unknown.
I had thought President Taft might be our most inbred president. Burke’s
Presidential Families of the United States of America, 2nd edition (1981)
states (p. 426) that the parents of President Taft (Alphonso Taft and his wife
Louisa Maria Torrey) were fourth cousins once removed. This relationship is
shown (p. 429) to be through their common descent from Robert1 Taft
and his wife Sarah. This information, and the more extensive chart of President
Taft’s ancestors in the appendix, is apparently based largely on Clarence Almon
Torrey’s outline of Taft’s ancestry in The American Genealogist
22(1945):205-210. Torrey’s outline, if one takes the time to work out an
ancestor table, shows that Alphonso and Louisa Taft have several more
relationships, although not as close as through Robert Taft and his wife. These
relationships are through:
1. Samuel2 Hayward and Mehitable Thompson (4th cousins twice
removed and 5th cousins once removed)2. John1 Hill and
Frances (5th cousins once removed and 6th cousins once removed)3.
John2 Thompson and Sarah (5th cousins twice removed, and again 5th
cousins twice removed; 6th cousins twice removed, and again 6th cousins once
All connections are important if we really want to assess the genetic
relationship of the couple. These additional connections would seem to make
Alphonso and Louisa very closely related, but actually they only double their
genes in common over that from their descent from Robert1 and Sarah
Taft. This doubling of their genetic relationship, however, is not sensed in
the terminology we use to define cousinship. The doubling of relationship
changes Alphonso and Louisa from fourth cousins once removed to a relationship a
little closer than fourth cousins. This is still a far closer relationship than
that of an average married couple in the United States. For those interested in
presidential trivia, I believe President Taft was, physically, the heaviest
Chief Executive. The relationship between his parents makes him one of the
most inbred as well, with an inbreeding coefficient of 0.0012.
But then I recalled that President John Adams and his wife Abigail Smith were
related, thus making their son President John Quincy Adams somewhat inbred.
Burke’s Presidential Families of the U.S.A. (2nd edition, 1981) shows (p.
69) a third-cousin relationship between John and Abigail (Smith) Adams, making
the inbreeding of their son John Quincy Adams equal to 0.0039, a little over
three times Mr. Taft’s coefficient.
The highest inbreeding, however, is that of President William Henry Harrison
whose paternal great-grandmother was Elizabeth Burwell (ca. 1678-I 734), sister
of a maternal great-grandmother, Joanna Burwell (ca. 1674-1727) (see Gary Boyd
Roberts, Ancestors of American Presidents, preliminary edition, revised
119891, p. 13). The inbreeding coefficient of children of this second-cousin
marriage is 0.0156 -- four times that of John Quincy Adams. A further trivium
is that this President Harrison had the shortest time in office of any
president: one month.
In summary, the highest inbreeding among our presidents is
A further note: We all can find in our ancestry examples of first- or
second-cousin marriages, so this amount of inbreeding is not at all uncommon.
But in these three cases, the inbreeding is more than most of us have.
Inbreeding can have harmful effects, but in the actual cases of these presidents
it was still of such a low value as probably to have had no effects at all. So
the genetic effects of these inbreeding coefficients could be considered
“academic” and thus truly an item of trivia.
References for further reading on the subject of
L. L. Cavalli-Sforza and W.F. Bodmer, The Genetics of Human Populations
(San Francisco: W. H. Freeman, 1971).J.F. Crow, Genetics Notes,
7th ed. (Minneapolis: Burgess, 1976).D.S. Falconer, Introduction to
Quantitative Genetics, 2nd ed. (New York: Longman, 1983).Thomas
H. Roderick, Ph. D. is a geneticist at The Jackson Laboratory in Bar Harbor,
Maine. Interested readers may correspond with him at 4 Seely Road, Bar
Harbor, ME 04609.