When I first began lecturing at York University I had rather sort of megalomaniac fantasies. I always imagined myself sweeping forward towards the lectern in PX001 - that was the name of the main lecture theatre - PX001, with my gown trailing in my wake, much like Richard Burton in the film Candy and then I would turn slowly and dramatically towards a packed audience of students who were already leaning forward eagerly so as not to miss a single one of my apercus.

I'm slightly reminded of that fantasy because reviewers tend to invoke not altogether dissimilar images in their description of my next guest. I meanSteven Pinker may be a Professor of Psychology at Harvard University and a very distinguished scientific researcher but he is also - and I quote - "the thinking man's Malcolm Gladwell", "a wunderkind", "the tousled genius", "a campus superstar".

Now I can recognise this as little more than the academic jealousy customarily aroused by anyone who writes so prolifically and talks so fluently - but it becomes perhaps just a little less innocuous when it gets in the way of a proper appreciation of a major piece of scholarship - and that really is the only way to describeSteven Pinker's latest opus - The Better Angels of Our Nature - The Decline of Violence in History and its Causes.

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You'll probably have heard or read about this work already - it's been widely reviewed, widely discussed - so let me just give you a brief summary. This is the one - it's a bit impertinent of me but Stephen this is one I've nicked actually from you. You were asked for a précis which would appeal to a talk show host and this is what you said as your thesis:

"Believe it or not, violence has been in decline for long stretches of time, and we may be living in the most peaceful era in our species' existence. The decline has not been steady; it has not brought violence down to zero; and it is not guaranteed to continue. But it is a persistent historical development, visible on scales from millennia to years, from world wars and genocides to the spanking of children and the treatment of animals."

Well Steven Pinker now joins me - together withAnthony O'Hear, who is Professor of Philosophy at the University of Buckingham.

Stephen, you said, I think, when you began on this book that it grew out of a question 'what are you optimistic about'. Is this a sort of dinner party question?

Steven Pinker:
No, it was a question on an online forum - edge.org - and an annual question and I wrote a few paragraphs reiterating facts that I had long known, but that weren't that well appreciated, such as that the homicide rate in England fell by a factor of about 30 from the Middle Ages to the present.

Some facts that were well known - that a number of barbaric practices that were abolished during the enlightenment seemed to have stayed abolished, like breaking on the wheel and burning religious heretics at the stake.

That the Soviet Union fell with very little violence.

That our lives as hunter gatherers was almost certainly far more violent than even the worst years of the 20th Century, proportionally speaking.

Having said that I then received correspondence from scholars in a number of fields that I was barely aware of saying there was much more evidence for historical declines in violence than I even cited in that squib. The Second World War Memorial in Washington DC seen at night Creative commons image Credit: B Tal under CC-BY-NC licence The Second World War Memorial in Washington DC seen at night

Laurie Taylor:
Did the book get longer and longer and longer...

Steven Pinker:
Yes, it did.

Laurie Taylor:
You had this hunch but then all of a sudden evidence starts piling in from everywhere else?

Steven Pinker:
Evidence starts piling in.

I heard from the scholars who count wars and war deaths telling me that in the last 20 years there's been a precipitous decline in battle deaths throughout the world.

I heard from experts on child development who said that rates of corporal punishment and child abuse have gone down.

I heard from historical criminologists who say it's not just England that have a homicide decline since the Middle Ages but every European country.

And I realised that there's a pattern developing here, and that there really was a book in it. And the link also came from the fact that as I started to speak about it I got a slew of objections which I felt I had to anticipate when writing the book.

Laurie Taylor:
Let's see if there are any objections around the table here from Anthony O'Hear. Anthony, all these graphs, all these tables - they certainly appear without much doubt to demonstrate a numerical decline in violence over the centuries. Are you happy to say that a numerical decline in violence is a decline in violence?

Anthony O'Hear:
Well, I can't question the statistical evidence and the graphs, partly because I don't know the basis of much of it. So I mean I'm perfectly happy to accept this.

My feeling is that being shown a graph that homicide rates and violence has declined since the Middle Ages or since the time of Genghis Khan is not going to be much consolation if I'm one of the 100 million people that were killed as a result of Communism.

And I think that in USSR, China, Vietnam, Cambodia, Eastern Europe, Latin America, Africa, Afghanistan and other places - and I mention Communism because I think that it's a kind of lietmotif of Stephen's very interesting book that a lot of this decline in violence can be attributed to elements which arose during the European enlightenment.

But actually I see Communism as an outgrowth of the European enlightenment in the following sense: That it was an attempt to apply reason and science to human affairs and to spread benevolence everywhere. And that is a characteristically enlightenment theme.

So I think that we need a far more careful understanding of what's meant by the enlightenment in listening to Stephen's thesis which I think he says doesn't apply everywhere but only applies in certain areas - I mean, I think that's fair enough.

Laurie Taylor:
Just going back to the first part of your response there - are you wanting to say that there's a certain danger in talking about the decline in violence because it distracts us from the very real sufferings that are going on at the moment, it provides us, if you like, with a bogus reassurance?

Anthony O'Hear:
Well I'm going to be quite Evelyn Waugh-ish here - quantitative judgements do not apply if I'm the person who's being attacked - and plenty of people are still being attacked. So I don't think we should be at all complacent about this, and I don't know that you are, Stephen.

Steven Pinker:
No, not complacent. Numbers apply anytime you use a word like more, less, better or worse.

In other words whenever you make a claim about just about anything and it's true that proportions aren't consolation to the knowings of people who are killed in the 20th Century, but they might be consolations to the billions of people who weren't killed, who would have been killed, if rates of violence had stayed the same.

As to the enlightenment, I think it would be a stretch to blame the Gulag on David Hume and Spinoza and Emmanuel Kant and Descartes and Adam Smith...

Anthony O'Hear:
I was thinking also of Marx, actually.

Steven Pinker:
Yes. And I'm quite precise in what aspect of the enlightenment that I credit with much of this decline of violence, more closely associated with the Scottish and American enlightenment than with the French and German occurrence.

This is the idea that the locus of value is the individual sentient being and that social arrangements ought to be designed to maximise the flourishing of sentient beings.

I consider that very different from Marxism, which I attribute actually more to the German counter-enlightenment than to the Scottish and American and British enlightenment, in which the unit of analysis is a group, in the case of Marxism a class, and moreover that saw history not as a spreading benevolence but quite the contrary; that history is driven by a constant conflict, a particular class struggle and that the only way to a better world is by the subjugation of one group of people by another.

So we have to argue about what the word enlightenment means but I'm being very precise here as to what aspect of the enlightenment I'm crediting the decline of violence to.

Anthony O'Hear:
Yes, and I'd like to press you a bit on this because I'm not sure that what you're calling the enlightenment can sort of carry the burden - the good burden indeed - that you're attributing to it.

I notice in your epigraph to your book you quote Pascale and I will want to quote Pascal back to you: The strength of reason, infirmity of reason.

I think that reason can help us to be sceptical but I'm not sure that reason in itself can sustain the values of humanitarianism, cosmopolitanism and human rights, which you want to see as arising from the Aufklarung, from the reasoning of the enlightenment.

It seems to me that all those values can be quite strongly attacked by other reasons and I don't see you talk a lot about the escalator of reason as if once you're on the escalator of reason you inevitably get pushed in these directions.

Laurie Taylor:
Pushed away from violence?

Anthony O'Hear:
Well, not pushed away from violence but pushed - well possibly yes - in the direction of humanitarianism, cosmopolitanism and a kind of quality of human rights. I may agree with some of that, but I think you need more than just reason to take you there, because I think there are equally powerful reasons - reasons that would be intelligible to thinkers of the stature of Plato, Aristotle and Nietzsche against all those things.

In other words reason can't do it on its own and I think you miss out a very important aspect of what happened in the 18th Century which may be we'll come to in a second.

Laurie Taylor:
Stephen.

Steven Pinker:
I don't know what these reasons would be. The argument that I make is that once you have a community of rational agents who first of all value their own wellbeing and, granted that can't be deduced by reason, that has to be a given.

Anthony O'Hear:
Yeah, so it has to be a given.

Steven Pinker:
That has to be a given, so that - indeed that cannot be deduced, although any entity that has held itself together against the ravages of entropy long enough to be reasoning in the first place is very likely to take steps to protect its own integrity and wellbeing.

And also that a reasoner would be part of a community of other reasoners with whom it can exchange information.

That too is not logically necessary but given what we know about how things evolve, namely that your evolution takes place in populations, it's a reasonable characterisation of how intelligent agents are likely to evolve in this universe.

Given those two things the reason that I - and I can't take credit for this and greater thinkers than I have made this argument - is that as soon as we start to hash out how we are to live our lives the discussion is going to tend to go in a particular direction.

If I don't want you to harm me and I say here's some reasons why you shouldn't harm me, I can't state them in a way that allows me to harm you. I can't say I'm special because I'm me and you're not, and hope for you to take me seriously.

As soon as you get the rational debate going, it's going to move in the direction of universality, namely social arrangements that can be stated in a disinterested way of which the various formulations like the categorical imperative, the golden rule, the veil of ignorance are, I think, all different versions of the same core insight.

Laurie Taylor:
I know you want to come back Anthony but I just want to pick up on this word evolution because this - this is something which is been very significant to you in the past; you're typically described as an evolutionary psychologist. So I just want to tease out what's going on in this book and the theoretical implications of the title of your book because you talk about 'the better angels' of our nature.

The argument here, as I understand it, is that human nature, which is an evolutionary element, changes in the same way as physical characteristics change as a result of evolution; that this nature has demons, which you characterise: five inner demons, four better angels.

And then you want to say that given this human nature with this propensity for evil and for good that, as I understand it, certain circumstances - socio- and cultural circumstances, things that sociologists would recognise - impact upon these and lead some of these, in this case to this book, the decline of violence, lead to the four better angels, if you like, being favoured over the demons, something within these historical circumstances and you itemise them, you have a long list - the pacifism, civilisation, humanitarian revolution, we've talked about the enlightenment as being one of these long peace, the rights revolution.

Now is human nature changing as a result of the impact of all these various sociological forces upon that human nature?

Steven Pinker:
It's not impossible, and I discuss that possibility in the book. Biologically, it is conceivable that some of the declines that have unfolded over millennia and even centuries could have led to changes in gene frequencies that could be said to alter human nature.

However, I'm very conservative about invoking changes in human nature. I note that some of the declines in violence that are quite powerful have unfolded over the span of decades or even years, that is way too fast to be attributable to biological evolution and I say given that we know forces that can reduce violence without biological evolution, the parsimonious explanation is we don't need to invoke changes in human nature.

Laurie Taylor:
So if we are not talking about evolutionary changes in human nature towards a more passive predisposition, this would then mean that a change in sociological circumstances could lead to a reversal of that which you've been describing?

Steven Pinker:
It could, yes.

Laurie Taylor:
So the arrival of new forms of scarcity, over-population of the world, whatever - all of these elements could reverse the process. But you seem to feel that it's not going to be reversed?

Steven Pinker:
Well, I think that some aspects of progress are unlikely to be reversed. When our ancestors got rid of human sacrifice it pretty much stayed abolished and that's probably going to be true of developments like the abolition of slavery, the equality of women, the decriminalisation of homosexuality.

On the other hand politics can give us some nasty surprises and I would not predict that a return to widespread civil war is impossible.

Laurie Taylor:
Anthony, your reaction to this account of human nature and its modifications.

Anthony O'Hear:
Well, I don't think it has been modified, and I believe in original sin, so I don't think that we're ever going to have a state in which we can simply relax. I mean, I agree very strongly with one part of Stephen's book that we have to have strong sensible institutions that allow this peaceful life to develop.

Laurie Taylor:
So when you say you believe in original sin, are you citing a religious concept. Or are you just simply talking about the intrinsic malevolence of human beings?

Anthony O'Hear:
Yes.

Laurie Taylor:
Okay.

Anthony O'Hear:
And it seems to me that what's rather scandalously missing from Stephen's account is any nod in the direction of Christianity. He says the scriptures present a god who delights in genocide, rape and slavery, he doesn't, as far as I can see, mention the New Testament.

And if you want to know where ideas of humanitarianism, and possibly cosmopolitanism, come from I think you could look to Christian thinkers who were extremely influential during the 18th Century, including on the Founding Fathers, who I greatly admire.

And I think that Stephen quotes Hume as saying: "Reason is and ought to be the slave of the passions", I think for many people at that time the passion for compassion was Christianity and it was precisely blamed for that by Nietzsche, who disagreed with a lot of these things.

Laurie Taylor:
I hate to say this to you Stephen with such a short amount of time to go - but your response [to that?].

Steven Pinker:
I don't think that Christianity deserves the credit for these declines in violence. One thing you have to explain away the Crusades, the European wars of religion, the colonisation of the Americas in which people were killed if theyweren't converted at sword point, the persecution of homosexuals and also what was it that changed in Christianity in the 18th Century that made it so much more humane - I think it was the same occurrence that brought the enlightenment.

Laurie Taylor:
And there we will have to stop. Steven Pinker, Anthony O'Hear, thank you very much.