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Jimmy Doherty in Darwin's Garden: Peacock feathers

Updated Tuesday, 24th February 2009

Jimmy Doherty visits a peacock farm to explore the evolutionary value of those fabulous tails

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Jimmy Doherty: The reason I’m here is because I’m trying to find out what Darwin was interested in with the peacock, and it seems to me that he was extremely interested in the peacock’s tail and the purpose it serves the peacock, because it just wasn’t there for show.

Marion Petrie: Yes, that’s right. I mean he was very worried about the peacock’s tail because he couldn’t understand how something so clearly useless could have evolved in terms of his theory of evolution by natural selection. It has a survival disadvantage, a tiger in India can, you know.

Jimmy Doherty: Yeah, if you’ve got a great big long tail you can't fly up in a tree, that’s got to be a bad thing, so it’s got to have a real purpose now hasn’t it.

Marion Petrie: Exactly. And he couldn’t see at first how it could evolve. And he once said the sight of the peacock’s tail whenever I gaze at it makes me sick.

Jimmy Doherty: Really? But also Darwin would have loved to have done the detailed research you’ve done, so I mean if he was today looking at the work you’ve done over the years I think he would be extremely happy.

Marion Petrie: Yeah, he was very interested in manipulating the peacock’s tail because he was the first person to come up with the idea that it could have evolved through female choice. So what he wanted to do was to persuade a peacock breeder to actually remove all the eye spots, or remove the tail and then see how attractive the male would be to females. But he thought that no peacock fancier would actually agree to it.

Jimmy Doherty: But you’re the dedicated peacock farmer so your job is to breed wonderful peacocks.

Quintin Spratt: That’s right, yes.

Jimmy Doherty: But how do you feel when Marian goes round chopping their tails off, because that’s like this.

Quintin Spratt: Well we keep a lot of stock so we allow for Marian to butcher some of them if she needs to.

Jimmy Doherty: Yeah, do you think hang on Marian, I’ve spent ages getting that peacock just so and you come along and you give it a haircut.

Quintin Spratt: Yeah.

Marion Petrie: Well it’s not butchering it. It’s just trimming a few eye spots, and in fact I mean if you make something look really odd, outside the range of normal, then clearly it’s not a very good experiment. So the idea is just to remove a few eye spots, make it less attractive than it was.

Jimmy Doherty: Okay, because the peacock’s tail has lots and lots of eyes on but do some males have different amount of eyes than the other males on their tails?

Marion Petrie: Yeah. Yeah, the range goes from about 180 eye spots at the low end to about 220. So we were concerned of making sure that we produced, you know, manipulation that was within that normal range of variation. So we actually snipped off about 20, which is.

Jimmy Doherty: Okay, so ...

Marion Petrie: And it’s, you know, they produce a new train every year.

Jimmy Doherty: Oh so it’s not a bad thing having a bit of a trim.

Marion Petrie: Oh no, it’s like a haircut.

Jimmy Doherty: Well exactly, but the idea is that the peacock with the fewer eyes gets fewer girls?

Marion Petrie: Yeah, I mean in a good experiment you need a control group, and so the idea, what we did was actually record a male’s mating success in one season, then over winter before the start of the next mating system we reduced the number of eye spots on a group, and then we compared that to a control group whose mating success we recorded but whose eye spots we hadn’t played with.

Jimmy Doherty: Okay, so you’ve got something to compare with then haven’t you.

Marion Petrie: Yeah, that’s right.

Jimmy Doherty: So this experiment, we’re going to do a bit of a simplified experiment because you’ve done it over many years, so the equipment that we need is just a pair of scissors, is that right?

Marion Petrie: Absolutely right.

Jimmy Doherty: And a few peacocks.

Marion Petrie: And a few peacocks, yes.

Quintin Spratt: And somebody able to catch them.

Jimmy Doherty: Well that’s, this is your expertise, you’ve got to catch them and that’s hard work. So shall we crack on then?

Marion Petrie: Absolutely, as long as I don’t have to do the catching.

Jimmy Doherty: You’ll be alright.

Quintin Spratt: Right, they’re particularly in those carts over there, I don’t know if we can get hold of that one, it would be quite good if we could get it in the corner. I’ll just get the net in the ... just quickly grab both legs. Have you got them? So they don’t stress too much, that’s the thing. Just hold him there like that.

Jimmy Doherty: Hold it down unless he relaxes.

Quintin Spratt: Just let him hold down, yeah, rather than pick him up just take him ... there we are.

Jimmy Doherty: A beautiful tail on him.

Marion Petrie: He’s absolutely gorgeous.

Quintin Spratt: There we are.

Marion Petrie: The eye spots start a bit below the Y, and what we would do would be to take, trim 20 eye spots.

Quintin Spratt: I’ll set up and then I’ll count them for you.

Marion Petrie: Okay, and we take the longest.

Jimmy Doherty: And how old would this peacock be to get to its full length, or its full tail to grow?

Marion Petrie: Well this bird will be at least four years old. They develop the full train at age three.

 

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