Female Promiscuity: Darwin's Benefit of the Doubt

If you have been following this blog, female philandering in various animal species should come as no surprise to you.  (If you have not been reading along but are interested, check this out. Or this.) 

However, a new book by scientist and author Tim Birkhead illustrates how the greatest naturalist of all time got it wrong.  And how generations of scientists also got it wrong as a result.

In his book, The Wisdom of Birds: An Illustrated History of Ornithology, Dr. Birkhead discusses one of the biggest misconceptions in the study of animal behavior: that female songbirds are sexually monogamous.  Most songbird species are socially monogamous, forming pair bonds in which one male and one female cooperate to raise offspring.  But it wasn't until the last decade or so that we could determine with DNA fingerprinting that the male in the pair is not always (quite often not!) the genetic father of the chicks in the nest. 

Mommy's babies are daddy's maybes.

So perhaps Charles Darwin can be forgiven for assuming that social monogamy is the same thing as sexual monogamy among songbirds when he wrote The Descent of Man, and Selection in Relation to Sex.  After all, Mr. Darwin knew nothing of DNA or genes.  Despite being a contemporary of Gregor Mendel, he missed the boat on the principles of inheritance we take for granted today.

Dr. Birkhead argues that Mr. Darwin should have known better.  After all, he observed it himself!  Darwin, like many gentlemen of his day, was a breeder of doves and therefore surely observed the occasional dalliance by pair-bonded females.  He knew about female promiscuity among thief pigeons - in which females were known to abandon a mate in favor of setting up shop with a sexier male. 

Dr. Birkhead discusses additional examples of female promiscuity described by Mr. Darwin and then addresses the question: Why, in the face of evidence to the contrary, did Darwin conclude that only males were evolving promiscuity under sexual selection?

Interestingly, it may have been due to his Victorian sensibilities: it was simply impolite to discuss such a scandalous notion as female philandering.  To compound matters, his daughter was his editorial assistant and he may have been uncomfortable sharing such conclusions with her.

Whatever Darwin's reasons, Dr. Birkhead argues that generations of scientists - including such ornithological  heavyweights as David Lack - went on to largely dismiss female promiscuity in birds because Mr. Darwin said it was unimportant!

I teach a course on Evolutionary Biology every academic year.  One of the first lessons in the class is that uncritical acceptance of any theory or idea is bad practice for a scientist.  That even though I consider Mr. Darwin's theories about natural and sexual selection to be powerful and well-tested ideas, as a scientist I must be among the most skeptical of them.

Dr. Birkhead's book is an excellent splash of cold water in the faces of uncritical scientists.  I believe it will make an excellent addition to my course reading list.