This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
In many species, male and females look different to each other. In these ‘sexually dimorphic’ species, males tend to be more ornamented. ‘Ornaments’ are basically anything that’s just for decoration with no other function, the classic example being the peacock’s tail.
Female and male humans are sexually dimorphic, but a lot less so than some other animals (I have often mistaken a women for a man, or a man for a woman, but I have never mistaken a peacock for a peahen).
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In some animals, females occasionally show rudimentary forms of male traits (the particular ornament of that species). An example in humans of a female showing a male trait would be male-pattern facial hair (i.e. beards).
So-called ‘bearded ladies’ have had a tough history, with the strong social stigma associated with having male-typical facial hair. Between the 15th and 19th centuries they were even paraded in front of audiences in circus ‘freak shows’.
As science progressed and as people learned more about how such previously mysterious anomalies arose, so society started to treat those who looked different to themselves less as ‘freaks’ and more as other human beings. Interestingly, freak shows apparently do still exist, but their proponents now put a different spin on it (see here to read about ‘Black Scorpion’
Male fence lizards are bright blue on their throat and on the sides of their body. A recent study has looked at how male lizards respond to female lizards that show a rudimentary version of this trait. They found that the male lizards discriminated against these females, choosing not to mate with them. The ornamented females (that I actually think look a lot prettier) reproduced less than the non-ornamented ones. They also produced eggs that hatched later, possibly because it took them longer to find a male to mate with.
Why might female ornamentation still exist in this species, if it is so detrimental? It is possible that ornamented females have some advantages outside of reproduction, for example being more socially dominant. It is also possible that these females produce better quality male offspring (with more or better ornamentation). However, the scientists did not find that the ornamented females produced more males than the non-ornamented ones, as you might expect if this were the case.
It is worth bearing in mind that this is just one species. In other species, such as some species of birds, ornamented females are actually more fecund compared to non-ornamented females. And of course, this says nothing about human ‘ornamentation’. At a fancy-dress party I was told that I was actually rather fetching with a moustache, and no one can deny that Johnny Depp looks good in makeup.
Photo Credits
Peacock & hen: Darkros
Deer: Caroline Granycome
Annie Jones: Poster, author unknown
Fence lizards: Lindsey Swierk and Courtney Norjen
Male fence lizard: Jarek Tuszynski
Reference
Swierk L, Langkilde T. 2013 Bearded ladies: females suffer fitness consequenceswhen bearing male traits. Biol Lett 9:20130644.