John Sutherland: Your book is called The Case of the Female Orgasm. Is it really such a mystery?

Elisabeth Lloyd: Yes, female orgasm is very mysterious. Nor has science thrown much light on it. In my book I examine 20 explanations which turn out to be completely unsupported by the evidence. They were hopelessly bad science. I like good science.

JS: You suggest that the female orgasm is an "appendix", of no more evolutionary value than my nipples.

EL: Male and female both have the same anatomical structure for two months in the embryo stage of growth, before the differences set in. The female gets the orgasm because the male will later need it, just as the male gets the nipples because the female will later need them.

JS: So the female orgasm is not a biological adaptation with evolutionary advantages - it's just a light nature forgot to turn off?

EL: Yes. But my view isn't necessarily the right explanation. It's just that at this time it's the best explanation that's supported by evidence. I'm quite open to the idea that orgasms may well turn out to be an evolutionary adaptation. And I actually spell out in my book research pathways that I'm urging should be followed to find out whether they are.

JS: How did you start on this particular line of research ?

EL: Well, I had a background. My dissertation was on the structures and confirmations of evolutionary explanation. Very rigorous. The current state of evolutionary explanation is on a level, you know, with the highest level of science today. But I'll tell you how I got started on this particular topic. I was 26. It was a very, very hot summer night and I was having more than a couple of calming peach daiquiris with a girl friend of mine, another philosopher, and she asked me, out of the blue, "What is the evolutionary function of female orgasm anyway?" I was completely surprised. "I have no idea," I said, "I'll look it up for you." And so I trotted off to the library and I looked it up and I found a bunch of sources and I read their explanations and they were stunning, because they violated the standards of scientific confirmation on which I had so carefully written about in my dissertation. And I thought, "Wow! this is horrible science." And it caught my eye. Why was this science so bad? And I looked up more and more and they were, you know, worse and worse. And I realised I had a case study here. Kind of "science gone astray". It was 40 years of science that didn't self-correct.

JS: Is the "uterine upsuck" thesis - which suggests the female orgasm causes contractions that "upsuck" sperm to aid conception - among that bad science?

EL: Oh yeah. That has been widely accepted in the community of scientists for the past 12 years - ever since Robin Baker and Mark Bellis published their research in 1993. But unfortunately the evidence for it is really badly flawed. In one of their tables 73% of the data came from one woman. It's really quite shocking that for 12 years this research has been taught as "fact" all across the US, Canada and the UK.

JS: The adaptationists have counter-attacked, haven't they?

EL: There have been a couple of savage reviews in the scientific journals. But if you read them it's very noticeable that although they attack the major findings of my book they don't defend any of the 20 adaptive accounts I attack and it's clear they tacitly agree that none of these adaptive approaches are acceptable. What they do is they say that adaptationists will need to look to the future for their evidence. They don't, for example, defend the Baker/Bellis account.

JS: So you are an evolutionist?

EL: Oh Lord yes. I've been an evolutionist since childhood. I read a book on evolution when I was six years old and I became fascinated with it. I still have the book that my parents bought - a Time-Life book with a lot of pictures in it called Evolution. It came out in 1963.

JS: You've also been attacked by some feminists, who use adaptationism to argue that orgasm is pleasure and pleasure leads to eager participation. Are they right?

EL: I'm so glad you said that. I make very clear in the book that of course sexual pleasure and stimulation is adaptive. The clitoris itself is adaptive in its promotion of intercourse and in its stimulating sexual excitement and lubrication and all of that. It's clearly adaptive. Of course anything that makes any woman want to have intercourse is adaptive. But there is simply no evidence that the physical reflex of orgasm itself is adaptive. That's a very important distinction. If that were the case orgasm would correlate with an increase in the number of children. The women who are orgasmic would have had to have contributed more genes to the future.

JS: And over the evolutionary time-span they would have become a majority?

EL: Exactly. Over evolutionary time we would have pretty much all orgasmic women. We don't.

JS: Why does something that began with a conversation between two liberated women over peach daiquiris provoke such anger among feminists?

EL: Well, I think it's pretty straight- forward. What they heard, when they heard the media accounts of my book, was, "Lloyd says evolution doesn't care about orgasm" and they also heard, "Lloyd doesn't care about orgasm, doesn't think orgasm is important." Everyone, even women, in our male-dominated society wants to think orgasm is important. That's what's going on. They were responding to the media reports. The media weren't interested in the feminist aspects of my analysis in which I did show that a number of the accounts - not all, but a number - were in fact male-biased. They didn't present my work as also being a feminist analysis.

JS: It looks like you've mobilised a pretty formidable axis against yourself: misapprehending feminists, male-biased scientists, the religious right who get nervous at any mention of sex. Does that worry you?

EL: Well, you know there is a reason why I didn't publish this book until I'd got all my ducks in a row as far as the evidence went and my career set.

· Elisabeth Lloyd is professor of the philosophy of biology at the University of Indiana at Bloomington

· The Case of the Female Orgasm is published by Harvard University Press