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From the book The Red Queen by Matt Ridley:

In an astonishing study recently undertaken in Western Europe, the following facts emerged: Married females choose to have affairs with males who are dominant, older, more physically attractive, more symmetrical in appearance, and married; females are much more likely to have an affair if their mates are subordinate, younger, physically unattractive, or have asymmetrical features; cosmetic surgery to improve a male’s looks doubles his chances of having an adulterous affair; the more attractive a male, the less attentive he is as a father; roughly one in three of the babies born in Western Europe is the product of an adulterous affair.

Shocked? Wait... the quote goes on:

If you find these facts disturbing or hard to believe, do not worry: The study was not done on human beings but on swallows, the innocent, twittering, fork-tailed birds that pirouette prettily around barns and fields in the summer months. Human beings are entirely different from swallows: Or are they?

After some more paragraphs, one finally finds some data on humans:

(…) [Baker and Bellis] have tried to measure the extent of cuckoldry in human beings. In a block of flats in Liverpool, they found by genetic tests that fewer than four in every five people were the sons of their ostensible fathers. In case this had something to do with Liverpool, the did the same tests in southern England and got the same result.

I posted the first paragraph above because immediately after I had read it I was about to post it here... Then I read the next paragraph which explained that they were talking about swallows.

These are my questions: (1) Are the Baker & Bellis statistics creditable? That is, are there other sources with similar results? (2) The Baker & Bellis studies are from the 1980s. Given that they are creditable, do the same statistics hold today? (3) Is there a website or something that keeps statistics of this sort, perhaps about other places besides Liverpool?

Thanks.

  • Do you have a link to the statistics / studies of Baker & Bells. Two blocks of flats doesn't necessarily mean definite proof, it would better to see the size of the study and any conclusions they tried to draw on the data. All you have provided is an authors view on a study which appears to be small scale. Although it is creditable, doesn't necessarily mean it is credible. – going Sep 13 '11 at 5:59
  • +1, excellent question; I've had this book on my 'to-read' list for quite a while. But if it cites this kind of "studies"... I might skip it. – Mihai Rotaru Sep 13 '11 at 10:30
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    Wait... someone performed cosmetic surgery on swallows? For a study on bird adultery?!? – Beofett Sep 13 '11 at 13:24
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    @Beofett: IIRC, the "size" and "symmetry" referred to the swallows' talis; the researchers were clipping on fake tails. (as I recall from the Red Queen book) – Piskvor left the building Sep 14 '11 at 9:00
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    @MihaiRotaru: I would recommend the book. It's damn interesting and crammed with good ideas. – becko Sep 21 '11 at 3:23
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Since the 1940's, numerous studies have been published regarding paternal discrepancy; here's a fairly comprehensive list. Also, four meta-studies ( literature surveys ) are listed.

Bellis is listed as both the co-author of some of the individual studies, and a 2005 meta-study. Quote from the abstract:

Paternal discrepancy (PD) occurs when a child is identified as being biologically fathered by someone other than the man who believes he is the father. This paper examines published evidence on levels of PD and its public health consequences. Rates vary between studies from 0.8% to 30% (median 3.7%, n = 17). Using information from genetic and behavioural studies, the article identifies those who conceive younger, live in deprivation, are in long term relationships (rather than marriages), or in certain cultural groups are at higher risk.

From a similar survey of 67 studies, published in 2006:

Evolutionary theory predicts that males will provide less parental investment for putative offspring who are unlikely to be their actual offspring. Crossculturally, paternity confidence (a mans assessment of the likelihood that he is the father of a putative child) is positively associated with mens involvement with children and with investment or inheritance from paternal kin. A survey of 67 studies reporting nonpaternity suggests that for men with high paternity confidence rates of nonpaternity are (excluding studies of unknown methodology) typically 1.9%, substantially less than the typical rates of 10% or higher cited by many researchers. Further crosscultural investigation of the relationship between paternity and paternity confidence is warranted.

The Straight Dope article on paternal discrepancy also mentions this study, and comments:

Seen this way, the numbers yield a pretty convincing pattern. The median nonpaternity rate for the high-confidence group was a not-too-scandalous 1.7 percent, whereas the low-confidence group showed an unsurprisingly high rate of 29.8 percent - about what one might gather from watching a few weeks of Maury Povich. If you combine the first group with the can't-conclude group, which showed a rate of 16.7 percent, you get a rate around 3.3 percent, or a ninth of the low-confidence rate. While Anderson cautions that there's currently no way to figure out what percentage of total births are low- or high-confidence, and thus what a societywide nonpaternity rate might be, he does use figures from a paternity confidence study he conducted in Albuquerque to guess that the rate for that city as a whole would be under 4 percent.

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