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The Breaking Science team come to BBC Radio Five Live to break open this week's science stories.

Darwin and evolution

Celebrating the 200th anniversary of Charles Darwin's birth - and considering his work: Darwin and evolution.

Why is Charles Darwin commonly held up as the father of the theory of evolution? Ben Valsler spoke to Darwin biographer Jim Moore, and he began by asking him what drove Darwin to formulate the concept of evolution in the face of what was, initially, profound religious and political hostility to his ideas.

Jim Moore: Darwin was driven by different things at different times, just like all of us. He was complex; he changed; he became more conservative generally speaking as he got older, but if you mean what drove Darwin to become an evolutionist, one has to say it has to be something as powerful as the forces that were ranged against evolutionists.

When Darwin is less than 30 years old, he comes back from travelling around the world – most of it was on land, not at sea – but he gets home, and within weeks, probably a few months, he’s become an evolutionist. Why does he do that? It’s a bad career move, and in our new book, Darwin’s Sacred Cause, Adrian Desmond and I say that that powerful drive that overcame the social stigma of being an evolutionist was Darwin’s radical belief in the unity of all life.

That common descent unites every species, the human race as well as all races of animals and plants, and that leads him to a powerful image that was part of the ideological foundations of the anti-slavery movement. The notion of a family tree of humanity for traditional Christians rooted in Adam and Eve as the father and mother of humankind. Darwin takes it a step further and unites everyone and says that it’s our arrogance to believe that we’re not related to animals; it’s the arrogance of the slaveholder lording over his slaves whom he likes to regard as another species.

Charles Darwin. Image: Jupiterimages Corporation.

Ben Valsler: This may well have been the driving force but still, it was a long time before he published. It was a long time before these ideas actually made it out there. Was there a tempering force as well that made him look for all the right evidence and made him make sure he could prove this before he would publish?

Jim: Darwin kept his thoughts to himself to begin with. He was in the process of becoming involved in the Royal Society as secretary of the Geological Society of London. He was welcomed to the inner sanctum of elite natural history. His sponsors were Cambridge clergymen, professors; he had a grant from the Whig Chancellor of the Exchequer, a huge amount of money to publish his Beagle research. He was a young man on the make. He was pushing all the right buttons, he was going all the right places, and yet he carried this terrible secret in his private notebooks. He needed a theory, and he began calling his speculations ‘my theory.’

That was his project, ‘my theory,’ and towards the end of 1838 he works out what we now call natural selection. By 1839, when he’s getting married and having children, he’s developed that, and he knows within three years – he leaves London, he takes shelter in the countryside – he knows he’s onto something really big. It’s going to change the course of the history of science if he can convince people.

Now, at that stage you don’t go public. You take every precaution that’s necessary to convince people beforehand that what you carry with you is true. It’s not disreputable; it’s the answer to the mystery of the diversity of life on earth.

So, he commits himself for the next 17 years, that’s sort of 20 years in all since he devises natural selection, to answering in advance every conceivable objection that the heavyweights of science in his day could bring against what he’s doing, and that leads him into huge research projects. And finally he gets around to putting pen to paper and he plans a huge book, maybe a half million words in three volumes which no one would read, and in the middle of all of that, you know, he gets outed by this guy named Wallace, everyone knows this story, Darwin has to condense his work into something which he entitles On the Origin of Species.

Ben: Do you think the pressure of having these other younger researchers formulating very, very similar theories based on very similar principles, Wallace was looking at series of islands much like Darwin had, do you think this forced him to make some concessions in his work?

Jim: Darwin was not aware that Wallace was working on a theory, until the paper arrived in June 1858. Darwin felt safe in his non-competitive ecological niche as a theoriser of evolution. He knew that all the other theorisers were discredited or spoke ill of. He wasn’t like them. He wasn’t telling anybody what he was like. He still believed he had an inside track on natural selection.

Now, what did he do with that theory once he knew that Wallace was onto the same thing? He believed Wallace was onto the same thing. Darwin read the paper in haste; we can all see now that they are not talking about the same thing in the same way – Wallace rejects the selection analogy for example. Absolutely basic analogy with domestic animal breeding, Wallace absolutely rejects it, always rejects it. So there’s a fundamental difference between Darwin and Wallace to begin with.

I can’t see that Darwin gives up anything. I’d have to think about it for a while before I gave you a technical answer, but it seems to be that what Wallace says and does over the next 10 to 15 years makes Darwin more attached to what he always thought. Wallace did push him hard, and Darwin said once, “It terrifies me to disagree with you,” and that was public hyperbolae, but this unprepossessing sort of guy, who left school when he was 13, he didn’t go to Cambridge. I mean he would have, Wallace would have joined The Open University and he’d have got a fine PhD, had there been an Open University in 1840.

This was an incredibly bright and underused talent, you know, and Darwin knew that. You know, they were socially chalk and cheese, and yet this guy was dorking him, and Darwin took preventative measures, hedging about his theories to make sure, obvious example is sexual selection, Darwin is so goaded by Wallace, because Wallace doesn’t believe that male competition and female choice causes sexual dimorphism in nature.

Darwin expands his work on sexual selection so two thirds of his book, on ‘The Descent of Man’, and Selection in Relation to Sex is the rest of the title, two thirds of that book is about birds and bees and pigeons and furry mammals before he ever gets to humans. Typical Darwin, he has to do the whole panoply of nature to prove that sexual selection is right and (brackets) Wallace is wrong.

Ben: And finally, what was it about Darwin that means that he stands out now? There were other people researching similar things that may not have hit exactly the same theory, but Darwin really was the man that stands out as being the father of evolution.

Jim: Evolution needs a father, as Steve Jones would say. Newton is pictured by Blake’s geometer outside the British library on Euston Road - unfairly perhaps. You think of Einstein. You think of Einstein as a brain, you know. You might think of Freud as being something really slippery. But Darwin’s a grandpa! He has a beard. He has a big family. He’s wealthy. He lives in the country. He’s contented. He cut the image of what it was like to be a gentleman of science in his day, and he still does.

Darwin is cuddly. Apart from the fact that this old man is not reliable with children because he teaches them falsehoods, some people say, this old gent is like anybody’s grandpa. You could really warm to the guy.

Now I’ve studied Darwin for many, many, many years, and I’m not particularly enamoured of him. The more I’ve got to know him, I suppose the more I’ve got to know anybody, the less I’ve been enamoured of him.

Listen to the whole programme, originally broadcast on BBC Radio Five Live, March 2009.

Find out more

Explore the reality behind the man and his theories: Darwin

Watch Jim Moore talking about his discovery of Darwin’s motivation

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The Breaking Science team come to BBC Radio Five Live to break open this week's science stories.

The Breaking Science team discussed new research that might help our understanding of how we smell:

Kat Arney: They do say a rose by any other name would smell as sweet, but what does make us think that a rose smells nice but my feet smell bad? My feet don’t smell that bad. But until now scientists have known relatively little about how the smelly molecules, known as odorant molecules, are recognised by the receptors in our noses. But new research by Harumi Saito published in the journal Science Signalling this week could shed some light on this mystery.

Chris Smith: So come on then, tell us why does a rose to me smell like a rose and your feet smell, well let’s not go there.

Kat Arney: Well our sense of smell is an amazing thing and our noses have hundreds of olfactory receptors, each of which can pick up a different smelly molecule and this then sends a signal into the brain which gets interpreted as a smell. But we only know around about 50 of these smelly molecules and that somewhat limits our understanding of the whole system.

Chris Smith: So what are the researchers actually doing in this study to try and home in on what’s going on?

Kat Arney: Well they used a technique called high throughput screening which allowed them to carry out many, many experiments in a short time, and this allowed them to test 93 different odorants, these are the smelly molecules, against a panel of 464 different olfactory receptors, and they picked up 52 specific odorants that activate mouse receptors and the screen pulled out 10 new odorants that activate human receptors.

Smelling a flower.
[image © copyright Jupiterimages]

So this has, you know, made a big increase on what we know about the number of specific molecules that interact with the smell receptors. And the scientists used the knowledge from their screen to then develop a computer model that can help to predict what kind of odorant molecules might fit with different olfactory receptors.

Now it’s probably possible to look at a whole range of smelly chemicals and try and predict which olfactory receptors they might bind to. So this is basically going to speed up the process of research in this area so scientists will have better ideas of which routes to follow rather than just taking shots in the dark.

Chris Smith: It’s interesting because before Christmas I spoke with a perfumer who makes smells for a living, nice smells, and he had the chemical equivalent of synaesthesia, he could imagine a smell and see the molecule in his mind’s eye that would smell like that, so I guess he’d be very interested in a function or a model like that.

Kat Arney: Absolutely. Fascinating.

Listen to the whole programme, originally broadcast on BBC Radio Five Live, February 2009

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The Breaking Science team come to BBC Radio Five Live to break open this week's science stories.

The Breaking Science team met two researchers who’ve been following the hum of insect wings

Chris Smith: In some countries it’s traditional to woo or serenade a woman by singing beneath her balcony. Well now it turns out that things aren’t so different in the insect world. Here’s Lauren Cator.

Lauren Cator: I’m interested in how mosquitoes choose their mate, and my hypothesis is that they may use flight tone as a way to get information about the quality of potential mates.

Chris Smith: So in other words how fast the wings are flapping?

Lauren Cator: It’s not a direct relationship but that sound that’s created by the wings flapping, yes.

Chris Smith: So what was the big unknown then that you were trying to investigate here?

Lauren Cator: There was a paper published in 2006 by Gibson and Russell, and they found that in Toxorhynchites, a large non-blood feeding mosquitoes, that a similar behaviour was occurring, and, as a medical entomologist, I was interested in seeing if medically important mosquitoes, mosquitoes that feed on human blood and transmit pathogens that infect people, were doing similar things.

Chris Smith: Well this seems like a very good time to bring in Ben Arthur who’s another researcher on this paper. Ben, how did you actually investigate what was going on with these mosquitoes to see how they were tuning into each other’s wing beat frequencies?

Ben Arthur: Well it was a two-part study. We had behavioural methods and some physiological data as well. In the behavioural data, what we did was we tethered individual mosquitoes to a fine insect pin with some glue and positioned them next to a special microphone which could sense the wing flight tone very finely and just listened to what they were doing.

[Sound of mosquito]

So what you’re listening to right now is a male mosquito singing along at around 600Hz, and he’s next to a microphone. And we’re going to bring in a female here.

[Sound of mosquito]

And she’s singing at 400Hz. And the higher harmonics at 1200Hz, the shared harmonic, if you listen real close, you can hear the beats produced because those two frequencies are so close together. And that’s what’s happening when they’re courting.

Chris Smith: So which sex is changing its wing beats in response to the other?

Ben Arthur: They both do. So if the male’s relatively stationary and the female comes in she’ll modulate her tone up or down to match his, or if the female is stationary and then the male can move his and they’ll just synchronise to actively both match each other.

Chris Smith: You’re saying it’s not actually the frequency the wings are beating at, but the harmonics, the multiples of the frequency the wings are beating at, which seems to be important?

Ben Arthur: That’s right. So the natural occurring frequency of the female wing beat is at 400Hz and that of the male’s at 600 and those are different enough that they don’t try to match the fundamental but rather the shared harmonics are the integer multiple at 1200Hz.

Chris Smith: How does the mosquito that’s the recipient of these frequencies, how does it actually detect them, and how do you know that it’s actually responding to the frequencies, and then how does it then know, right now I need to mate?

Ben Arthur: Right, well it has these very plumose antennae, and these antennae sense the movements of the particles in the air, and there’s a sensory organ at the base of the antennae called the Johnston’s organ which transduces that movement of the antennae into an electrical voltage that the nervous system can then use to detect where the sound is, and what it is and whether it’s a mate or not.

And the second part of our study then recorded from the Johnston’s organ and saw these electrical voltages and we found that we could measure electrical voltages all the way up to 2kHz which includes that shared harmonic at 1200Hz.

Chris Smith: Wasn’t there some claim previously by other people though that mosquitoes a) were deaf anyway and b) that they couldn’t hear sounds that high in frequency, so you’ve really scuppered both those myths haven’t you?

Ben Arthur: That’s right, exactly, and we’ve shown it with both behavioural data and physiological data in the same paper.

Chris Smith: Lauren, what do you think that the major impacts - apart from obviously this being academically very interesting - what do you think the main other impacts are from a medical point of view?

Easy to repel - but how would you attract a mosquito?
[image © copyright Jupiterimages]

Lauren Cator: Well just generally we know very little about mosquito mating behaviour, and we have no idea who’s choosing who or how they’re choosing them, and one of the control strategies that’s been proposed is to create transgenic mosquitoes - so mosquitoes that through genetic manipulation are either unable to transmit pathogens or are sterilised. The idea would be that if you release these into the wild that males carrying your desired genotype would be able to compete with wild males for female mates, and drive the genotype through the population. Unfortunately we have no idea what constitutes a sexy male mosquito.

Chris Smith: Hopefully they’ll find out soon. That was Lauren Cator and before her Ben Arthur. They’re both based at Cornell University, and they’ve published that work in this week’s edition of the journal Science. And if you’d like to read a bit more about how animals use sounds to track down a mate or find their way around there are links to a number of articles about those subjects on the Breaking Science website.

You can hear the mosquitos - and the whole programme - on the Breaking Science website. This interview was originally broadcast in January 2009 on BBC Radio Five Live

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