Image copyright Getty Images

As The Selfish Gene notches up 40 years in print, BBC News asked Richard Dawkins whether his most famous book is relevant today (answer: yes), whether he has any regrets about public spats over religion (no), and whether he is quitting Twitter (sort of).

"I'd so much rather talk about this than about politics."

This, from a thinker most famous as a fearless firebrand, sounds rather incongruous. But as Prof Dawkins hunches over his laptop to dig up examples of biomorphs - the computer-generated "creatures" he conceived in the 1980s to illustrate artificial selection - it is transparently, genuinely felt.

Later, we touch on the fact that he sees public debate as a scientist's responsibility. Right now, he wants to talk about molluscs.

Pretend molluscs.

"I don't know whether you know the classic book by D'Arcy Thompson, On Growth and Form? He showed that all mollusc shells are a tube, which is enlarging as it coils around. You only need three numbers to specify a mollusc shell."

Those three numbers can be plotted inside a cube, Prof Dawkins explains. "Evolution is then just a walk through this cube of all possible shells."

In a computerised game he wrote in 1996, people could construct their own such walk by choosing for themselves which offspring would "breed" in successive generations of shells.

This game has now been resurrected online to mark the 20th anniversary of the book it arose from, Climbing Mount Improbable.

Its mollusc shells are presented alongside an ancestral explanatory exercise: the biomorphs. These were first programmed 10 years earlier, when Dawkins wrote The Blind Watchmaker. He clearly remembers getting lost in the work.

"When I discovered that I could actually start getting something that looked like an insect, I got really obsessed with the idea of breeding insects."

Image copyright Penguin Image caption The biomorphs are back

As the biomorphs grow from simple, branching stick-shrubs into more elaborate and occasionally familiar shapes, they make an important point - and one that is better grasped by being involved than by hearing it explained.

"You get much more of an idea of what it's like to breed dogs from wolves, or to breed cauliflower from wild cabbage," Prof Dawkins says, clearly enjoying the sight of the spindly shapes evolving again on his screen.

Like Darwin long before him, Dawkins settled on artificial selection - selective breeding for desirable characteristics, such as speed in race horses - to explain an important point about natural selection.

For Darwin, it was the idea that variations within a population, or herd, can persist and shape future generations if they are favoured by the breeder. If we humans can coax domestic dogs into their astounding variety of breeds then nature, with vastly more time at its disposal, can produce all the variety of life on Earth through a similar, slower selection process.

For Dawkins, the focus was the notion that has underpinned so much of his work: this process has no need for an architect. Slow, subtle preferences for one form over another will gradually produce complexity.

Image copyright Richard Dawkins Image caption The original Blind Watchmaker software eventually fell foul of operating system updates

The Blind Watchmaker, many scientists and writers agree, was Prof Dawkins at his finest. His arguments are made with infectious enthusiasm and powerful imagery.

Ten years earlier again, Dawkins' pioneering account of the "gene-centric" view of evolution, The Selfish Gene, also won huge acclaim.

It crystallised an argument that had been brewing since Watson and Crick's beautiful DNA structure marked a new peak in our understanding of inheritance: these sequences would tend to accumulate and propagate mutations that were beneficial to the gene itself. Any given gene "wants" to be passed on to as many future offspring as possible.

Forty years on, however, this concept faces some opposition among today's biologists.

The unapologetic gene

There were no genome sequences in 1976. We didn't know just how many genes we share with other organisms, how profligately they interact with each other, or how profoundly they are affected by the stretches of DNA in between them. These and other insights, some argue, require a reassessment of the gene's primary role.

Dawkins sees no such need.

"Scientists actually quite like being proved wrong. Unlike politicians, scientists like to say, 'I made a mistake.' This is how science proceeds.

"But I can't really say that with The Selfish Gene. I think it's been vindicated by modern developments."

His conviction that the gene is "the principal unit of natural selection" is undiminished by any evidence he has seen from the genomic era.

Media playback is unsupported on your device Media caption Prof Dawkins discusses 'biomorphs' during the 1991 Royal Institution Christmas Lectures

"If you ask what is this adaptation good for, why does the animal do this - have a red crest, or whatever it is - the answer is always, for the good of the genes that made it. That is the central message of the Selfish Gene and that remains true, and reinforced."

Much of the complexity that has been added to our understanding of how DNA works, Prof Dawkins contends, can be viewed as a continuation of the "environment" against which a gene is selected.

"We're used to the idea that a gene for green colour flourishes in a green environment. But what I've added in many of my books is that a gene sitting, not on a green background, but on a background of other genes in the species, gets selected by virtue of its compatibility with other genes in the gene pool."

Perhaps the most popular challenge raised against the centrality of genes is the evidence that elements beyond the DNA's sequence - "epigenetic" affects like packaging or molecular tags that control a gene's expression - can be inherited.

Prof Dawkins dismisses this as a flash in the pan, both in its evolutionary significance and in the "15 minutes of fame" which he declares it is enjoying undeservedly.

"Obviously we've long known that some genes are turned on, and other genes are not turned on, in different tissues. The trendy thing is the allegation that a few of these turnings on or off get passed onto the next generation.

"That's the bit that gets all the hype and doesn't deserve to."

That heritable switching, he remarks, affects "only a few genes" and fades after a few generations. "It's not of evolutionary significance; it doesn't go on in the way that mutation does - which is forever, unless it gets selected out."

Stepping back... slightly

Here, we glimpse the combative Dawkins that has become so familiar in discussions of religion. Already a standard-bearer for many atheists, when he wrote The God Delusion in 2006 he became a veritable field marshal.

It won him devotees, but lost some admirers. He has often declared it was "a necessary book to write", but does he ever think it was a step too far?

"I've stepped back," Prof Dawkins says. "I haven't written any more books along those lines. The God Delusion is a one-off. Not one that I'm ashamed of; I'm very proud of it. But it's a one-off."

Media playback is unsupported on your device Media caption Richard Dawkins speaks to Radio 4 Today about the future of evolution

As for his many public comments on the topic of faith - from religious schooling to the burka - he stands by them all.

"It's important to [be involved in those debates]. I think scientists need to get involved in that kind of thing."

And does that responsibility extend to debates that are clearly outside a scientist's academic field?

"Religion is not really a field that you can have. It's a non-field. And insofar as religion makes claims in the area of science - which it does, because it talks about creation, it talks about the nature of the Universe, it talks about the nature of life - to that extent, all scientists should be involved in it."

Some of the professor's most heated recent spats have unfolded on social media. He has qualified some of his Twitter remarks and lamented that medium's lack of nuance, but embraces it nonetheless.

Or at least, he used to.

"I've given up Twitter," Prof Dawkins says quietly but curtly. The tweets that appear in his name, apparently, are the work of the staff at his Foundation for Reason and Science.

"I occasionally ask them to post something, which they do, but I've given up doing it myself."

Might we be seeing a more wary, more restrained Richard Dawkins in future? This seems unlikely. But he is obviously pleased to turn the conversation back to science.

Image copyright OneZoom Image caption OneZoom assembles known species onto leaves and branches of a single "tree of life"

We conclude by discussing what challenges and benefits recent findings have brought to his theories; he is particularly excited by the way whole-genome sequences can inform our extended family tree.

As the technology gets cheaper and faster, Prof Dawkins says with excitement, "it will become possible to lay out the complete tree of life".

To emphasise the point, he returns to the laptop and opens OneZoom, a dazzling, all-encompassing representation of the tree of life which uses fractal shapes to allow continued expansion. (This map now adorns the website for another Dawkins book, The Ancestor's Tale.)

This is "an actual geography", he explains as we flit from one branch to another, instead of a series of linked pages like most such catalogues.

"It's sort of like Google Earth - but of the whole animal-plant kingdom. And they're now crowdsourcing it; you can sponsor an animal that they haven't yet got.

"I'm going to sponsor Verraux's sifaka - the lemur that dances with its hands in the air."

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