Malika Ihle
Department of Behavioral Ecology and Evolutionary Genetics
Max Planck Institute for Ornithology

Dear Malka Ihle:

I have read the abstract of your article 1) I accessed through PubMed, who mentioned the whole article as being free, but the button was not active.  Accordingly I have assumed that nothing of great consequence was omitted, although you know and I do not.

Since you are interested in mate choice, I’m sure you are acquainted with the work of Patrick Bateson 2).  He placed some Japanese quail in a cage so that a female could choose which male to stand near.  (Figure 2 If you would like to see the graph, go to 3 and dig around a bit.) She would spend the least time with a familiar sibling, next least with an unfamiliar sibling, the most time with a novel first cousin, less with a novel third cousin and by “unrelated” (of course we are all ultimately related, but it’s his word) novel male her interest dropped down almost as far as novel sibling.  When it was done with a male choosing, the result was essentially the same. 

So Japanese quail, it would seem, given the chance prefer to mate with kin.  This is not a dysfunctional move.  The work of Sibley et al. 4) shows that for smaller populations – which necessarily means closer average kinship – of birds and a number of other animals there is a faster growth rate of the population.  Mate with a cousin and have more babies.  The same phenomenon has been demonstrated in humans 5) in Iceland.  Again, the graphs for 4) and 5) are there in 3). 

Superficially it may seem absurd.  Why would selection seem to favor mating with kin when we’ve always been told that diversity is good, good, good?  You can dig through note 3), but it might be simpler just to go to a brief sketch I did for the Swedish department of public health 6).  It turns out that it is not only possible but inevitable. 

So the good news is that your zebra finches may have sorted each other out by kinship and when those kissing cousins (billing and cooing cousins) were separated, things didn’t go so well.  You may have finch genealogical records that could rule this in or out.  If so, then either way it is a whole new paper for an evening’s work without even applying for a grant.  (It might be a late night, of course.)

It all comes down to mate choice, doesn’t it?  The whole history of the world is the history of people, and what people do is largely who gets born, and that is pretty much a matter of mate choice.  In fact it seems from the data that there is very little choice to be made in life other than that of mate.  And you never know what you’re getting.  See the included document.

The bad news … oh, forget the bad news.  It’s at the bottom of that letter to Sweden, but a reasonable and prudent person probably wouldn’t touch it. 

All the best,

M. Linton Herbert MD

1) Ihle M, Kempenaers B and Forstmeie W, Fitness Benefits of Mate Choice for Compatibility in a Socially Monogamous Species, PLoS Biol. 2015 Sep 14;13(9):e1002248. doi: 10.1371/journal.pbio.1002248. eCollection 2915

2) Patrick Bateson, Mate Choice (Cambridge University Press, Cambridge 1983


4) On the Regulation of Populations of Mammals, Birds, Fish and Insects, Richard M. Sibly, Daniel Barker, Michael C. Denham, Jim Hope and Mark Pagel SCIENCE vol. 309 July 22, 2005 page 607

5) An Association between Kinship and Fertility of Human Couples Agnar Helgason et al. SCIENCE vol. 329 no. 5864 February 8, 2008 page 813 – 816


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