Peacocks are famous for their long, beautiful tails.
They use these in courtship displays for peahens.
But why are these tails so amazingly big? Let's see what science has to say about peacock tails.
To see how peacocks got their tails, let's first see what they do with them.
The peacocks spread out their tail feathers into a fan. The fan is covered in eyespots.
They also shake their feathers in a specific way to make the eyespots jiggle.
The peahen looks at this display and sees... something.
Maybe tail length. Maybe the number of spots, which is also
based on tail length. And she makes her choice as to whether this peacock is a good partner.
Where did this preference come from, and where did the long tail come from?
Runaway Selection is the most popular theory as to how the peacock got its tail.
But runaway selection relies on a specific set of conditions to work.
Let's assume there is a gene for tail feather length. Second, and more controversial,
let's assume there is a linked gene that makes longer tails appealing to females.
This is the weakest part of the whole theory and we can come back to it,
but it's one of the conditions needed to make this theory work.
In the distant past the peacock had a shorter tail. There were a variety of
genes but they averaged around short. In the distant past the peahen had a
mild preference for longer tails. There were a variety of genes but they averaged around "meh".
If a more selective female pairs with a longer-tailed male,
both parents will contribute genes for longer tail and
tail preference. Remember, we said the genes are linked, so both parents have them. Their female
offspring will be more selective and their male offspring will have longer tails.
This population is experiencing
a selective pressure and gradually changes to increase fitness.
This process keeps turning with each generation.
More selective females pair with longer-tailed males.
Meanwhile, the rest of the population has mild or no preference, so there is no selective
pressure going the other way, other than the increasing absurdity of tail length, that is.
But if the tail preference is strong enough, the tails can get
amazingly long. And that could be how the peacock got its tail.
So is there a gene or set of genes for female preference? If there is, we have not found it yet.
If there is no such gene, then we will have to change our model for how the peacock got its tail.
Runaway selection can also affect things other than looks. Besides that long tail,
the peacock also has an extremely loud call to attract peahens from far away.
[peacock call]
Once they get close though, it's the feathers that to the job of impressing the peahen.
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