how many bastards are there, anyway?

Lee Rudolph (
4 Aug 1996 11:09:56 -0400

In May, 1994, I posted to AFU the lengthy extract from Jared
Diamond's _The Third Chimpanzee_ which follows below as Appendix 2.
In brief, Diamond's claims are that "between 5 and 30 percent of
American and British babies [have been] adulterously conceived",
that this was first discovered--but not published--by "a
distinguished medical scientist" (who he calls Dr. X)
investigating blood types in the 1940s, and that "several
similar genetic studies which did get published" (but to
which he does not give citations) "later confirmed" Dr. X's
results. No discussion followed this post to AFU, alas.

Yesterday I was talking to a bioethicist who studies genetic
counseling, and when the conversation turned to folklore, she
brought up an issue she'd recently investigated. She told me
that essentially all genetic counselors believe that there is a
"false paternity" rate of about 5 percent--yet few if any
counselors encounter a rate nearly that high in their own
practices. This discrepancy having piqued her curiosity, my
friend had tried to track down just why the rate is believed
to be 5 percent. One source after another said the scientific
equivalent of "it was published by a friend of a friend".
Eventually the FOAF-chain terminated, in a single paper whose
author does not think it supports the interpretation it is
popularly given! Appendix 1, immediately below, represents the
present state of her research into this possible piece of genetic

I'm posting this to sci.anthropology and
as well as AFU, with followups set back to AFU only.
I (and I am sure my friend) would be very interested to
have citations to Diamond's supposed "several similar genetic

Lee Rudolph

---begin Appendix 1---

(found at;
author is Dorothy Wertz, PhD, ``a bioethicist who has written
extensively about international aspects of genetic counseling'')


False Paternity

At the beginning of this century, as scientists began to understand
the idea of blood types, it became possible in some cases to prove
that a particular man was not the father of a particular child. Only
very recently have we acquired the means to establish with a very high
degree of certainty that a particular man is the father of a
particular child. If DNA based paternity testing had been available in
the nineteeenth century August Strindberg, the great Swedish
playwright, would probably not have written The Father, the plot of
which develops around a woman's decision to create doubts in her
husband's mind about whether he really is the father of their

False paternity is one of the most difficult problems that can arise
in the genetics clinic. If paternity is not correctly attributed, then
the calculation of recurrence risk in future pregnancies for a couple
who have a child with a single gene disorder will be wildly
inaccurate. In general clinical geneticists perform this calculation
without actually checking paternity; they rely on what they are told.

But, what is the "background false paternity rate" - the chance that a
randomly selected trio of couple and child who assert true paternity
will, if studied, yield a finding that the husband is not the
biological father? For decades many clinical geneticists have
suggested figures ranging from 2% to 5%. Using the high figure, this
would mean that 1 in 20 Americans have a biological father who,
unbeknownst to them, is different from their social father.
Conversely, in 5% of cases a child that a man regards as his is
actually the biological child of someone else.

When we tried to track down the scientific studies that support using
this range of estimates, we could not find them. Every clinician to
whom we talked seemed to know somebody who knew the scientific basis
for the data, but each query led to a dead end. Had we stumbled onto a
bit of genetic folklore?

A historical search and a conversation with Dr. James Neel, one of the
deans of human genetics, led us to what may be the source for the high
estimate: a 1962-65 study of blood typing in a small Michigan town
(1). That study found discrepancies between biological and stated
parentage in 109 of 2507 nuclear familes. Many of these may have been
unacknowledged adoptions, including step-parent adoptions.

We would be very interested to learn of other studies that support or
challenge assumptions about background false paternity rate. We would
also be interested in learning about any other examples of genetic

(1) Sing, CF et al (1971) Studies on genetic selection in a completely
ascertained Caucasian population II. Family analysis of 11 blood group
systems. American Journal of Human Genetics 23(2) 164-198.


---begin Appendix 2---

The following four paragraphs are quoted, for purposes of discussion,
from pp. 85-86 of _The Third Chimpanzee_ by Jared Diamond (professor
of physiology at UCLA), ISBN 0-06-018307-1 (Harper-Collins, 1992).

People have many reasons to lie when asked whether they have
committed adultery. That's why it's notoriously difficult
to get accurate scientific information about this important
subject. One of the few existing sets of hard facts emerged
as a totally unexpected by-product of a medical study, per-
formed nearly half a century ago for a different reason. That
study's findings have never been revealed until now.

I recently learned these facts from the distinguished medical
scientist who ran the study. (Since he does not wish to be
identified in this connection, I shall refer to him as Dr. X.)
In the 1940s Dr. X. was studying the genetics of human blood
groups, which are molecules that we acquire only by inertness.
Each of us has dozens of blood-group substances on our red blood
cells, and we inherit each substance either from our mother or
from our father. The study's research plan was straightforward:
go to the obstetrics ward of a highly respectable U.S. hospital;
collect blood samples from one thousand newborn babies and their
mothers and fathers; identify the blood groups in all the samples;
and then use standard genetic reasoning to deduce the inheritance

To Dr. X's shock, the blood groups revealed nearly 10 percent of
these babies to be the fruits of adultery! Proof of the babies'
illegitimate origin was that they had one or more blood groups
lacking in both alleged parents. There could be no question of
mistaken maternity: the blood samples were drawn from an infant
and its mother soon after the infant emerged from the mother.
A blood group present in a baby but absent in its undoubted mother
could only have come from its father. Absence of the blood group
from the mother's husband as well showed conclusively that the
baby had been sired by some other man, extramaritally. The true
incidence of extramarital sex must have been considerably higher
than 10 percent, since many other blood-group substances now
being used in paternity tests were not yet known in the 1940s,
and since most bouts of intercourse do not result in conception.

At the time that Dr.X made his discovery, research on American
sexual habits was virtually taboo. He decided to maintain a
prudent silence, never published his findings, and it was only
with difficulty that I got his permission to mention his results
without betraying his name. However, his results were later
confirmed by several similar genetic studies whose results did get
published. Those studies variously showed between about 5 and 30
percent of American and British babies to have been adulterously
conceived. Again, the proportion of the tested couples of whom
at least the wife had practiced adultery must have been higher,
for the same two reasons as in Dr. X's study.

---end Appendix 2---