Bred In The Bone

A large number of species form monogamous pair bonds. It may not be until death does them part, but for a while anyway. The evolutionary advantages look simple and clear, as jobs such as defending their patch and bringing up offspring are shared. But not everything is as straightforward as it appears on the surface.

In many of these harmonious families, males outside the pair have fathered a considerable number of the offspring. Forstmeir et al from the Max Planck in Seewiesen have been watching the surreptitious dalliances of female zebra finches with various birds about town (1). This behavior doesn’t appear to hold any advantage for the females. Indeed, it could be disadvantageous to the bond.

The research has shown that there is a hereditary element. The propensity of the finches to get together outside the pair is in the genes of both sexes and then a fraction of the young males will have a positive selection to grow up to be Latharios with a very persuasive manner.

The genetic basis of choice of mate took on an additional flavor with the work of BeBruine et al from the Us of Aberdeen and Stirling (2). Apparently women with brothers make different mate choices than women without. Not, I hasten to add, because of approval or otherwise from the brother(s). Having a brother makes the woman feel less attracted to a man who has any resemblance to herself, thus, helping her to hook up with someone right outside the family.

Having a younger brother is a greater safeguard against inbreeding than an older one. Yes, well, younger brothers are always a pain, aren’t they? Women without brothers don’t have this pressure. They can be as narcissistic as they wish.

The perception of trustworthiness is not effected, however. Perceiving a man who looks like you as being trustworthy is not a function of having a brother or not. So I guess that, on balance,  a younger brother might be a good thing for a girl to have.


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