Having spent last weekend on a farm that had a pair of peacocks. Obviously one had a large tail, which was periodically ‘on show’. This got me wondering about the how and why.
It’s one of nature’s most famous examples of “style over substance.” While those massive, iridescent trains look like a heavy burden (and they are), they exist for a very specific evolutionary reason.
The Theory of Sexual Selection
In the animal kingdom, survival isn’t just about staying alive; it’s about passing on your genes. This leads to Sexual Selection, a concept that was originally pioneered by legendary researcher Charles Darwin.
- The Peahen’s Choice: Female peacocks (peahens) are the primary drivers of this trait. Over millions of years, they have consistently been proven to chose to mate with the males who possess the largest, brightest, and most symmetrical tails.
- The “Eye” Count: Research also suggests that peahens pay close attention to the number of eyespots (ocelli) on a tail. A male with more eyespots has been found that they will have better mating success.
The “Handicap Principle”
You might wonder why evolution would favor a tail that makes it harder to fly and easier for other wild animals and predators to catch you. This is known as the Handicap Principle:
- A Test of Strength: A large, heavy tail is a burden. By successfully carrying it around and staying healthy, the peacock is essentially saying, “I am so strong and have such great genes that I can survive even with this ridiculous disadvantage.”
- Health Indicator: The vibrant colors and intricate patterns on the tail are hard for the bird to maintain. If a peacock is sick or has parasites, you will find that his feathers will look dull. A bright, shimmering tail is a “certified health certificate” for the female.
The “Rattle” and the Show
It’s not just about the looks of the large feathered tail; it’s also a performance.
When a peacock fans his feathers, he also vibrates them at the same time to help create a low-frequency sound (infrasound) that humans can’t hear but peahens can feel. This “shivering” also makes the iridescent feathers shimmer, creating an impressive optical illusion that the eyespots are hovering in place.
Fun Fact: Technically, the “tail” is actually called a train. The peacock’s real tail is a set of much shorter, stiffer feathers underneath that help prop the long train up during the display.
