Among the many incredible things that retiring Rajasthan High Court judge MC Sharma said on Wednesday, his explanation for why the peacock is India’s national bird was the most curious. “The peacock is a lifelong brahmachari” or celibate, he said. “It never has sex with the peahen. The peahen gets pregnant after swallowing the tears of the peacock.”

The video is worth watching, if only to see the reporter keep a straight face (starting at around the third minute).

The quote naturally led to plenty of hilarity on Twitter, which had already spent much of the day chuckling about Donald Trump’s covfefe.

Some even decided to correct the record by pointing out that peafowl, contrary to the judge’s belief, do actually copulate – even if they may also cry.

Indeed, peacock sex is no trifling issue. The sexual preferences of peafowl actually have an important role to play in our understanding of how interactions between genders works, and none of it has anything to do with tears.

Darwin’s theory

Charles Darwin, the scientist and explorer who developed the theory of evolution, was for years disgusted by peacocks. The sight of the bird’s beautiful tail feathers, he wrote in 1860, “makes me sick!”

This distaste was brought on by the fact that Darwin had been developing his theory of evolution, first set out in the Origin of Species, which had been published in 1859. Peacocks seemed too beautiful to fit into his idea of natural selection, where only the fittest survive. Darwin was struggling to convince people that God had not created every creature for human delight, what is now known as creationism, and that instead nature pushed animals to adapt to their surroundings and evolve features that would make it easier to survive.

But Darwin could not quite see how a peacock’s long, beautiful tail might fit into this. The tail actually makes life more difficult for a peacock, since it is harder to both run and fly with such a heavy weight behind you. If every animal had evolved to be fittest, how would evolution explain the aesthetically pleasing but horribly impractical fact of a peacock’s tail?

Sexual selection

Answering that question led Darwin to the theory of sexual selection, one that is as important to our overall understanding of evolution as natural selection. Darwin concluded that the peahen, just like humans, could appreciate the beauty of a peacock’s tail. And that might help a peahen select which peacock it chose to mate with. Instead of an evolutionary advantage that made it easier for peacocks to survive, the tail might be a sexual advantage, making the male more attractive to the female.

“A girl sees a handsome man and without observing whether his nose or his whiskers are the tenth of an inch longer or shorter than in some other man, admires his appearance and says she will marry him... So I suppose with the peahen; and the tail has been increased in length merely by on the whole presenting a more gorgeous appearance.”  

Darwin would eventually extend the theory of the peacock’s tail, thanks to work by Bernard Peirce Brent, a writer and “bird fancier” who provided him with information and specimens, and published a detailed account of courtship among birds.

As the Darwin Project explains it, “Brent gave it as his opinion that the spreading of the peacock’s tail was a ‘sexual ask’ to which the females might or might not respond depending on their fertility cycle, and Darwin went on to argue that such elaborate plumage could have been acquired, through sexual selection, in small successive steps.”

And that is how we get from a peacock’s tail to the theory of sexual selection, in small successive steps. Darwin put aside his belief, common to many in his age, that the female gender is inferior, and developed a theory that gave most of its agency to the females.

If it had not been for the peacock’s tail, Darwin might have been stuck at “survival of the fittest”, a theory that was not enough to explain the complexity of natural life, which can often seem beautiful but impractical. How Darwin might have responded to Justice Sharma’s tears theory, however, is sadly something we will never know.