Naked Evolution

01 July 2008
Presented by Ben Valsler, Dave Ansell.

It's 150 years since Darwin's theory of Evolution was presented to the Linnean Society, and so we've Naturally Selected the Science of Evolution! We find out why scientists have revisited a textbook example of natural selection in action, find out why horny sheep are gambling on good weather and how bacteria in the lab can evolve into a new species! We find out why tragedy almost kept Darwin's ideas from ever being seen, by looking at the archives of his own letters. Plus, why crocodiles chat from inside their eggs, a new way to send messages underwater and why Martian soil would be good for growing cabbages! And in kitchen science we find out which surface is best for keeping ice cool.

In this episode

01:58 - Eggs-ceptional hatching strategy

Scientists have discovered that baby crocodiles talk to each other from inside their eggs in order to synchronise hatching.

Eggs-ceptional hatching strategy

Scientists have discovered that baby crocodiles talk to each other from inside their eggs in order to synchronise hatching.

Baby CrocodilesWriting in Current Biology, Jean Monnet University researchers Amelie Vergne and Nicholas Mathevon recorded the sounds made by a clutch crocodile eggs in the time leading up to hatching.  They then played these sounds back to another group of eggs that were due to hatch within the next ten days.  Surprisingly, most the eggs answered back, and many of them also moved around!  But most importantly, all of them hatched out within ten minutes of hearing the sound.

As a control the team played random noise to another group of eggs, and left a third clutch in silence.  Neither of these two groups showed any calling or hatching response.  To find out why the crocodile hatchlings might be showing this behaviour the team also played the pre-hatching sounds, and some random noise, to nesting adult crocs in a zoo.

The adults responded by digging, moving or turning their heads to the egg-sounds, but not to the other noises.  This, the researchers think, is a survival mechanism on the part of the hatchlings to time their emergence when adults are likely to be nearby to protect them from predators.

The authors point out that birds are also known to make noises from the egg that encourage parental care, and as birds are closely related to dinosaurs - birds and crocodiles may have inherited this behaviour from a common evolutionary ancestor!

Reversing time to talk underwater

Communications on land have come on in leaps and bounds over the last 20 or 30 years; for relatively little money you can buy a phone which will transmit hundreds of thousands of characters every second, or you can buy a satellite phone which means you can talk to your mum from the middle of the Gobi desert.

Conversing underwater though, isn't so easy. The problem is that, because seawater conducts electricity, it absorbs radio waves, which means that once you get more than a few metres below the surface there is no point trying to tune into your favorite radio station.

Alvin submersibleSound waves, on the other hand, will travel through water very well, for example whales use them to communicate over thousands of kilometres. The problem is the echos, sound waves will bounce off the surface of the water, the seabed, shoals of fish, even layers of warm and cold water.

This means that if I shouted to you you would hear a whole series of overlapping versions of  my conversation and it would sound like gobbledy gook. This means that you have to communicate very slowly to wait for the echos to die down.

However William Kuperman and colleagues at the Scripps Institution of Oceanography have used a very neat method to get around this problem. If I wanted to send a message to you, first he would get you to play me 2 noises one to represent a 1 and another to represent a zero. I would then record how that sounds to me. Then I would reverse the tape and play them back to you, this means that the echos will cancel out the time reversal and you will hear a loud clear version of what you sent me with much less overlapping. This means that I could play the two sounds in a pattern to represent a message. This is what William Kuperman has done, and he can now transmit 15kbit/s over 5km and 5kb/s over 15km which is 3-4 times faster than normal links.

This is not just important for talking to submarines, but the bottom of the ocean is less well known that mars, and it will probably be explored by robotic rovers which will of course need to communicate with the surface.

Ancient Poet Astronomically Accurate

A few weeks ago on the Naked Scientists we followed the story of the Odyssey, and how although the land has changed in the 3000 years since it was written, the poet knew his geography.  Parts of the poem allowed modern scientists to locate the Island of Ithaca, even though the island has now been swallowed by it's neighbour!

Solar EclipseIt seems that the poet was also astronomically accurate, as researchers from Rockefeller University report in the journal Proceedings of the National Academy of Sciences.  Homer accurately describes a total solar eclipse, even though it happened nearly 3 centuries before the poem was written.

The passage reads "the Sun has been obliterated from the sky, and an unlucky darkness invades the world" - a pretty good description of an eclipse, but was it just artistic licence, or describing real events which occurred during Odysseus' long journey back to Ithaca?

To find out, Constantino Baikouzi and Marcelo Magnasco searched the text for additional astronomical clues, such as which planets were visible at the time and which stars the hero used to navigate by.  The big clue was a reference to the westward flight of the god Hermes, who represents the planet Mercury. Mercury appears low in the sky, and reverses it's course, East-West, every 116 days.

Baikouzi and Magnasco could use this data to scan all the possible dates that would fit all of these conditions, knowing that in order for a total eclipse to occur, you must have a new moon.  All of these conditions only occur together once every 2000 years  One of those matches is April 16th 1178 BC - fitting exactly with Odysseus's 10 year journey home from Troy.

We will never know if the events described to have taken place really happened during the eclipse - but it seems the description of the eclipse itself was more accurate astronomy than artistic artifice!

08:02 - Martian soils good for growing cabbages

NASA's Phoenix lander which landed almost a month ago is revealing the make-up of the soil on Mars...

Martian soils good for growing cabbages

NASA's Phoenix lander which landed almost a month ago has started giving us our best view of the Martian soil yet.

CabbagesThe lander is sitting on a plain near Mars' northern ice cap and has been digging in the soil and measuring its properties. After some problems in getting some soil inside, because it was too lumpy, the thermal and evolved gas analyser run by William Boynton, has heated some soil to 1000 degrees Celsius and measured the gases coming off. Analysis is still going on but it has apparently definitely interacted with water in the past.

The Microscopy, Electrochemistry and Conductivity Analyzer, or MECA has been giving a microscopic view of the soil and mixing it with water to try and understand the chemistry of the soil, what is dissolved in it etc.

These are the first wet chemistry experiments done on any planet other than Earth.  The results show that the soils are very similar to some Antarctic dry valley soils; they have found useful nutrients, such as magnesium, sodium, potassium and chloride, although the pH is 8-9, making it quite alkaline but suitable, apparently, for growing cabbages!

12:49 - Updating Evolution Evidence - The Peppered Moth

The evolution of the Peppered Moth is a textbook example of adaptation in the face of changing environmental conditions - yet the design of the original experiments have been criticised....

Updating Evolution Evidence - The Peppered Moth
with Dr Remy Ware, Cambridge University

Dave - Dr Remy Ware is from the Department of Genetics at Cambridge University where they've been going through the experiments that got the Peppered Moth in the textbooks. First of all, can you tell us what the original story was?

The Remy - Yeah sure. There was an original observation made in 1848 in Manchester in which there was a dark form of the so-called Peppered Moth recorded.  The Peppered Moth, its normal form is light in colour with a black speckling which gives it its name.  In 1848 the first black or melanic form of this moth was recorded.  Towards the end of the 19th century, towards 1895 or so, a very large proportion of the moths found in Manchester were of this darker form.  A very distinguish Victorian lepidopterist called JW Tutt proposed a hypothesis for why this was occurring.  His was of differential bird predation.

The idea was that with the industrial revolution the pollutants produce such a sulphur dioxide and soot fallout had darkened the surfaces of the trees on which these moths rest.  A combination of killing off the foliose lichens on the trees and actually darkening the surfaces themselves meant that what was previously a well-camouflaged light moth on a light surface now stood out very conspicuously to predators and suffered a higher predation rate such that a new mutation causing a melanic form of the moth was at a greater advantage of being more cryptic on the surface. 

Following this hypothesis a chap called Bernard Kettlewell in the 1950s tried to really test what was going on here.

The Dave - So basically the birds - if you're flying along and you see a black moth on a black tree you're not going to see it, whereas all the white ones are going to get eaten really quickly.

Remy - Simply a case of looking cryptic against your background so being light and camouflages on a light surface or being black and camouflaged on a blackened surface.

Dave - So the more black ones survive the more will be in the next generation.  There'll be more and more of them around for future generations.  There's been some criticism of this experiment.  What was that?

Remy - Ok.  This chap Kettlewell started trying to test the hypothesis of this bird predation.  More recently over the past decade or so his work's been criticised.  Mainly because of issues to do with it being very artificial.  What he actually did was he had an experiment in which he looked at an oak woodland in Dorset and a polluted woodland in Birmingham.  He looked at the levels of predation of the different forms of the moth: the light form versus the dark form.

He found a reciprocal result in his data.  More of the dark form were predated upon in the lighter area.  The criticism was that it was rather artificial for many reasons.  Firstly he was using a mixture of lab-bred moths and wild caught moths so they may not have been behaving naturally.  Also he was placing them in very conspicuous places on the tree.

Dave - So naturally moths would have hidden themselves?

Remy - Yeah.  Later experiments would involve gluing dead moths onto the tree in positions that were rather conspicuous.  We know now that moths naturally rest under twigs and under branches and things.  Also he was releasing moths in very, very high densities so essentially he was creating what we would call a bird-table effect.  The birds were learning that they could come to this site and they would have a good lunch straight away.

It's really these criticisms of artificiality which have been at the forefront of the arguments against the Peppered Moths case.

Dave - I guess he was still showing that there was a selection pressure towards the dark ones in the dark trees and the light ones in the light trees but people weren't entirely convinced.

Remy - Yeah so whatever the criticisms are of it being artificial, it was the reciprocal nature of the results of the two areas that was so convincing.  Never mind the nitty-gritty of the quantitative nature of the case, quantitatively it seemed very convincing.  Subsequent evidence came from a reduction in the dark form of the moth following anti-pollution legislation later on.  This was rather convincing and shows, importantly, that evolution was not a one-way process - it can go back.

Dave - So you've now been looking at trying to fix some of the problems with this experiment to try and answer its critics. What have you been doing?

Remy - Some work led by my colleague, Professor Michael Majerus, he wrote a book on melanism in 1998 addressing this point and since then had a number of criticisms.  He set about systematically trying to correct the problems with the original story mainly removing these issues to do with it being a very artificial type of experiment.  He tried as much as possible to make it a natural experiment.  He was releasing moths in natural frequencies, very low frequencies, and this experiment took over seven years to complete because it was trying to be so realistic.

Dave - Very patient!

Remy - Yep!  Importantly he also allowed the moths to choose their resting positions naturally.  He released them overnight and allowed them to select their positions as they would do in the wild whereas Kettlewell was releasing them during the day.  It was more likely they would select natural positions.  Various things like this and natural density could be why it took such a long time to do.  It sort of addressed each point in turn.

Dave - What was the result of the experiment?

Remy - Similarly to what was found by Kettlewell, again he found - this work was done in Cambridge - it was found incredibly convincingly that there was a very strong correlation between observed declines in the dark form in Cambridge between 2001 and 2008.  It's just been published now.  He found there was a very close correlation between the decline of the dark form of moth during this time and the actual predation that he observed by eye.  He observed various birds taking these moths from the trees, differentially with respect to colour: with respect to black form or the light form. He found a very close correlation between the predicted decline in the dark form as a result of this predation compared to what was actually observed.

So it was very strong evidence that differential bird predation was responsible for this.

Dave - Brilliant. Thanks very much Remy. That's Remy Ware from Cambridge University on how experiments in evolution can themselves evolve and improve.

19:12 - Evolution in the Lab

Evolving organisms on a lab bench allows a perfect view of how they change over time - but sometimes they can surprise us...

Evolution in the Lab
with Professor Richard Lenski, Michigan State University

Professor Richard Lenski works at Michigan State University and in his lab he's grown over 40,000 generations of E. coli for over twenty years.  He persuaded the bacteria to evolve totally new characteristics and giving scientists new insights into how organisms adapt and change over time.

E. coli bacteriaRichard - I've always been interested in the tension between evolution being a random process at the level of mutations.  Yet natural selection provides a force that moves populations to become ever more adapted.  This experiment with E. coli has been designed to look at how reproducible evolution really would be if we could repeat it.  I created 12 lines of E. coli, all started from the same ancestral cell.  We've been propagating them in my lab for about 20 years now and the bacteria have gone though 40,000 generations and we're watching how they change and evolve.

Ben - What are the advantages of using bacteria like E. coli to observe evolution in the lab?

Richard - One of the advantages of bacteria is that they have such short generations.  Also they have very large population sizes so in a little flask in the corner of the lab we can have millions of cells.  What's really cool to me is that we can freeze the bacteria away.  That allows us to directly compare ancestral and evolved organisms.  Actually comparing the living organisms is not just fossils.  It's the real-live bacteria.  Imagine if we could bring Neanderthal back to life.  We might try to play a game of football with the Neanderthals and we could see how the organisms in their performance, not just in their fossil morphology, but in their real performance have changed over time.

Ben - What sort of evolutionary changes have you seen since your very first cell line?

Richard - One of the most important changes is that the evolved bacteria are demonstrably much more fit in this environment.  They actually grow twice as fast as the ancestors.  When you compete them the evolved bacteria kick butt.  The evolved cells are much larger.  We're looking at how they've changed in many other properties.  In particular in the last few years we've been looking at how they've changed in the genotype.  We're actually sequencing the DNA and finding the mutations that are responsible for their adaptation.

Ben - Recently you reported on a slightly more dramatic change that happened in that they seem to have been able to use a different source of food.  What had happened here?

E coli evolving in the labRichard - In this medium that we've been feeding them every day for the last 20 years they've been growing on glucose as the only source of energy that they can use that's in that environment.  Throughout this entire experiment we've had another carbon source that's been present in the medium.  It's called citrate.  One of the features that's been recognised of E. coli cells is that they're not able to use citrate as an energy source.  It can't get inside the cell.

Ben - So this is one of the defining features that makes them an E. coli bacterium rather than something else.

Richard - It is, pretty much. There are little grey areas around the edge that are rather technical but certainly the general property of E. coli, one of the defining characteristics by virtually all assays.  For 20 years they've been eating their glucose and not recognising there's an open niche, another resource in their environment.  One of the twelve populations suddenly woke up, as it were, in an evolutionary sense and said, "Hmm.  There's something else to eat.  There's a desert tray around the corner after we finish our glucose."  That population evolved this new capacity to use this new carbon source as an energy source.  What we've done has been to try to ask, "Could any of the populations have evolved that new trait at any point in the experiment?"  We've been trying to ask if the genetic context changed so that this new phenotype became possible by virtue of the more-or-less inconsequential differences that it accumulated in one population versus the other 11 populations.  We took advantage of the fact that we have all these time points frozen away in our freezer.  With an extraordinarily dedicated graduate student, Zachary Blount, he essentially went back to the freezer and started the evolution experiments over from different time points along the way to the evolution of this interesting new trait.  What he found was that only after a certain point in time did he ever find mutants that were able to use citrate as a carbon source.  A sort of accident of the genetic changes in one line versus the other lines had opened up this door that there was another possible way of making a living in this extremely simple laboratory environment.

Ben - So you need a series of smaller, seemingly irrelevant mutations in order to have this big mutation that lets you change your food source?

Richard - Yes.  It's very clearly established that there were many mutations in these lines and that some subset of them that occurred in this population set up the potential to then get additional mutations that gave this very interesting new trait or phenotype.  In this simple little experiment that we've been doing in my lab this one population of the twelve that we've been studying took a different road, got on a different evolutionary path and that influenced its subsequent potential.

25:54 - Evolution in the Wild - Horny Soay Sheep

In Soay Sheep, having the biggest horns means you're more likely to breed - but it also means you're less likely to survive your first winter...

Evolution in the Wild - Horny Soay Sheep
with Dr Alastair Wilson, Edinburgh University

Ben - So what is it you've found in the Soay sheep?

Adult Male Soay SheepAlistair - I should say this is work really led by a colleague of mine, Matt who's gone to Glastonbury today.  Matt has decided he wanted to take a closer look at how natural selection is really acting on these traits of horn size and growth.  As you said, if you're a male sheep it's pretty important to have big horns because when it comes to breeding time you actually have to fight with other males to try and get access to other females.  I guess what he expected and what we all expected was that bigger horns, faster growing horns were going to be better.  It turns out that some of the time that is the case.  There's also another layer of complexity which is that if you want to grow horns very quickly you've got to put a lot of energy into doing that.  The Soay sheep live on an island of St Kilda which is characterised by quite strong variation in the environment.  Every year we hit a time when the food runs out and conditions get really, really tough.  It turns out if you put too much energy into growing horns then you're very unlikely to get through the winter.  There's kind of a trade-off here and if you grow your horns too quickly there's quite a high chance of dying if you hit some bad conditions.

Ben - So the sheep are really taking a gamble then because they know that if their horns are as big as they possibly can be then they're more likely to have the success in later life but they are betting that their first winter will be quite a mild one?

Alistair - That's it.  You can kind of think of it as different strategies so if you have a good season coming up then it's definitely better to have gone for it in terms of growing your horns.  If you get that wrong you might end up dead in which case it doesn't matter how big your horns would have been because you're not going to get any breeding success the next season.

Soay LambBen - Does this mean the sheep are either born with the potential to have big horns or born with the potential to survive the first winter?

Alistair - It's a little more complicated than that but we've been able to find there's genetic variation for these traits and that translates to genetic co-variation between horn growth and survival.  What that means is selection is acting at the genotype.  It's not the case of a complete genetic predetermination between these genes will give you fast-growing horns and these will give you slower growing horns in that categorical way.  There are some genotypes that have a tendency to go in one direction or another and it's this genetic variation that natural selection can act on.

Ben - We've just heard about evolution in the lab and it's very easy in the lab to control the conditions under which your organisms are evolving.  In the wild obviously you don't have that option.  You can't say it's going to be this temperature this winter.  How do you actually study them?

Alistair - It's certainly tricky.  Obviously we've learnt an awful lot and we continue to learn an awful lot by studying evolution in the lab.  Really what we're trying to do is tackle those problems head-on in changing environments because if we want to discover how evolution works in the real, natural world then we are going to have to work out how we're going to change all these environmental variables - as I say temperature or population size or anything.  Fortunately ecologists have been working for decades on exactly what these variables do and exactly how they affect organisms such as Soay sheep.  The challenge we're facing is perhaps trying to integrate what geneticists can do in the lab with what the ecologists are telling us and to try and integrate these sources of complexity rather than avoid them as you would do in a laboratory.

Ben - Can you take a genetic profile of your population and then try and use that to estimate how well they will cope with say, a bad winter coming up.  Can you actually use the genes to predict the success?

Soay LambsAlistair - Well, I think we may not quite be there yet but that's I guess what we're working towards.  We're trying to get an understanding of how changes in the environment will affect natural selection and also the genetic variation of the different traits on which the selection can act.  I think it's important if we can start to understand how environmental change in any form can affect those parameters.  Then we can actually start to build changing environments into predictive models on phenotypic evolution:  evolution of traits.

Ben - Ok.  If the climate changes as we are predicting the climate should be warming up would this have an effect?  Would we expect to see bigger horns on these sheep as the weather gets hotter?

Alistair - Certainly a starting prediction might be that if the weather warms up we get fewer and fewer of these bad years.  The net result of that is going to be that selection is always going to favour fast growth in horns rather than sometimes favouring slow growth.  If that's he case then we're going to have an increase in, if you like, the net selection for faster growth.  We would expect evolution toward faster growing horns, yes.

Ben - What does this tell us about the way that selection pressures balance each other?  Obviously we have the sexual selection here which is that you need to have big horns to compete with the other males around and to actually breed.  We then have the external natural selection.  Does one drive the other?

Alistair - I guess you can look at this problem in different ways.  For me, I see it all as being different components of the total selection.  The key point is that selection can act in different ways through what we might call different components of fitness.  Whether that be reproduction or survival in your first year versus survival in your second year.  The idea really is, if we can get a handle on how these individuals are behaving throughout their whole lives across a range of environments then we can start to see how selection trades off either across different environments, different ages or through different components like survival and reproduction.  We can bring all of that together to try and have an idea of the total picture.

Ben - So when we say an animal is fit, and we're looking at survival of the fittest, it could be that they are very fit in one aspect but that would, in turn, make them very unfit in another aspect.

Alistair - That's it exactly and it can be a real problem.  Sometimes the things you can measure might be survival.  It may be much more difficult in your system to measure the number of eggs produced or something like that.  You can get quite a misleading idea of what selection is doing if you're only looking at one aspect of fitness at a time.  The challenge is to try to get a whole, complete picture of an individual's life perhaps - how its fitness is achieved through both surviving and reproducing.

33:38 - Charles Darwin - In his own words...

Charles Darwin's ideas on evolution were presented to the Linnean society on the 1st of July, 1858. 150 years on, we look through Darwin's own letters to find out more...

Charles Darwin - In his own words...
with Dr Alison Pearn, Darwin Correspondence Project & Malcolm Love

Ben - It's 150 years this week since Charles Darwin presented his ideas to the Linnean society - marking the first public outing of his theory of evolution.  I went to visit Dr Alison Pearn, from Cambridge University to learn a bit more about the man behind the theory.   Alison is behind the Darwin Correspondence Project, so I started by asking just what the project is...

Portrait of Charles DarwinAlison - It's pretty much what it says on the tin, really.  There are about 14,500 letters written both from and to Charles Darwin.  We are publishing complete transcripts of them.  They are available in hard copies and they are also going up on the web.

Ben - We have the books that Darwin wrote.  The books would be the distilled essence of what he wanted to communicate. Why would we need all the letters or the rough drafts?

Alison - The books are meant for public consumption.  They are the final, finished product.  There's a whole back-story.  An extremely interesting story of how those books came into being.  Darwin was not a lone genius who suddenly had an epiphany of an idea and suddenly wrote it down.   Darwin was somebody who worked away for many years and in enormous detail talks about amassing great quantities of facts. He did that largely through the medium of correspondence - the medium of letters.

Ben - Can we trace the development of his theories using his correspondence?

Alison - To a large extent, yes we can.  There were certain of his scientific colleagues with whom he did discuss ideas and certainly went into detail.  In particular in correspondence with Joseph Dalton Hooker who was director of the botanic gardens at Kew and Darwin's closest friend.  And with Charles Lyell who'd been an early mentor it is possible to see Darwin begin to discuss his ideas and collecting the evidence to support the arguments he was making.

Sir Joseph Dalton Hooker Charles Lyell Alfred Russel Wallace
Sir Joseph Dalton Hooker Charles Lyell Alfred Russel Wallace

Ben - Darwin and Wallace presented their ideas together to the Linnean society in July 1858 but if the correspondence shows he was discussing aspects of it only months before, what was it that galvanised him into presenting his findings instead of the long, painstaking work he'd been doing?

Alison - Well, famously it was the arrival of a letter from Alfred Russell Wallace who was out in the field in Malaysia.  Wallace had also written a paper which Darwin describes as being so uncannily like his own theory.  In some ways it was as if Wallace had actually seen his manuscript.  He actually panicked.  He immediately writes to Charles Lyell and to hooker, and is really is asking them what he should do.  It's actually Darwin's friends who were pushing to finish in what, to him, was an unseemly hurry.

When the papers were read at the Linnean Society neither Wallace nor Darwin was actually there.  Wallace was still out in Malaysia and Darwin was struggling with a completely different crisis in his life.  Two of his children were ill with scarlet fever.  Through the detail of the letters it's possible to see the alternating hope and despair as the children get sicker.  He's explaining to people that he can't respond to their letters, including Hooker, who is trying to get him to publish.  He's completely distracted by the illness of his children.  Just before the two papers were read at the Linnean Society his youngest child who was a baby, Charles Darwin, died.

"My dearest Hooker,

You will, and so will Mrs Hooker, be most sorry for us when you hear that poor Baby died yesterday evening. I hope to God he did not suffer so much as he appeared. He became quite suddenly worse. It was scarlet fever. It was the most blessed relief to see his poor little innocent face resume its sweet expression in the sleep of death. Thank God he will never suffer more in this world.

I have received your letters. I cannot think now on subject, but soon will. But I can see that you have acted with more kindness and so has Lyell even than I could have expected from you both most kind as you are.

I can easily get my letter to Asa Gray copied, but it is too short.

Poor Emma behaved nobly & how she stood it all I cannot conceive. It was wonderful relief, when she could let her feelings break forth.

God Bless you. You shall hear soon as soon as I can think

Yours affectionately

C. Darwin"

Ben - A personal tragedy like that must have been awful for him.  It must have almost made him give up.

Alison - It did.  It was only because it was his closest friend who had asked him to send the papers and a close friend with whom he could discuss his feeling on the death of his child that he was able to send the papers.  He writes a postscript to a letter in which Darwin, as an afterthought, says I've just realised that you want these papers now but I dare say I don't really care.   

"I daresay all is too late. I hardly care about it.

But you are too generous to sacrifice so much time and kindness. It is most generous, most kind.

I really cannot bear to look at it. Do not waste much time. It is miserable in me to care at all about priority.

God Bless you my dear kind friend. I can write no more."

Ben - It was about this time that Darwin's abstracts were presented to the Linnean society.  How did he react about this.  How did he feel?

Alison - Personal life was still included in a very big way during this whole period.  He was very concerned that the rest of the family might become sick and he writes to Hooker a few days after the paper.  The first thing that he's keen to say is that they have evacuated the children and they'll move their daughter as soon as she's well enough to go.

Ben - Family was still at the forefront of his mind?

Alison - Absolutely.  In all the letters in this period once the first child has become sick it's the family that are there first.  It's the first thing he mentions to everyone he's writing to at this point.  He does thank Hooker very sincerely for having watched his back and gone to so much trouble to make sure his name was associated with Wallace's in writing of the papers.  Although he says he's really ashamed of himself now for having cared about whose name was given.

"My dearest Hooker.

We are become more happy and less panic-struck, now that we have sent out of the house every child and shall remove Etty, as soon as she can move. You may imagine how frightened we have been. It has been a most miserable fortnight.

Thank you much for your note, telling me that all had gone on prosperously at the Linnean Society. You must let me once again tell you how deeply I feel your generous kindness and Lyell's on this occasion. But in truth it shames me that you should have lost time on a mere point of priority.

I do not in the least understand whether my letter to Asa Gray is to be printed; I suppose not, only your note; but I am quite indifferent, and place myself absolutely in your and Lyell's hands.

I can easily prepare an abstract of my whole work, but I can hardly see how it can be made scientific for a Journal, without giving facts, which would be impossible. If the Referees were to reject it as not strictly scientific I would, perhaps publish it as pamphlet.

We thank you heartily for your invitation to join you; I can fancy nothing which I should enjoy more; but our children are too delicate for us to leave; and I should be mere living lumber.

If you see Lyell will you tell him how truly grateful I feel for his kind interest in this affair of mine. You must know that I look at it, as very important, for the reception of the view of species not being immutable, the fact of the greatest geologist and [botanist] biologist in England, taking any sort of interest in subject: I am sure it will do much to break down prejudices.

Yours affectionately

 Darwin's Signature

With many thanks to the
Darwin Correspondence Project and
Malcolm Love.

42:07 - Why do copper compounds come in different colours?

Can you tell me why, copper the metal is “copper in colour”, yet it is blue when in solution with sulphate, copper carbonate is colourless in solution, and when you flame test the element...

Why do copper compounds come in different colours?

Dr Peter Wothers, Department of Chemistry, University of Cambridge:Metals in general reflect all of the light energy that comes on to them but copper doesn't reflect all of them. It absorbs part of the spectrum. It absorbs the bluey part of the light and maybe some of the green light and reflects all the coppery coloured light which comes back in to our eyes. That's what happens with the metal.

In compounds copper sulphate, the blue colour is due to the light energy being used to promote or excite electrons that are in the atom of the copper when it's combined with other things such as the sulphate or carbonate ions and so on. In solution what you actually have - in the same way when you dissolve salt in water you end up with sodium ions and chloride ions not bound together any longer as they are in the crystals but surrounded by water - the water interacts with the copper ions. The colour that you see isn't really copper sulphate, it's copper ions surrounded by lots of water.

Copper carbonate the solid doesn't have the same water there and this is usually a greenish colour. Incidentally the copper sulphate, the crystals itself are blue but that's because they also have water trapped in their crystals. If you heat them up and drive out the water they actually go white and colourless. It's the waters there that are interacting with the copper ions.

Finally the flame test, why does the element test produce a green flame? This again is energy being used to excite the electrons in the atoms or ions. When this energy is returned, is given out again as the electrons fall back down to their low energy levels it gives out only part of the spectrum. It gives out green light.

Will dry ice sublime quicker on metal than wood?

Basically, yes. Dry ice doesn't actually melt. It sublimes straight to a carbon dioxide gas. That takes energy so the more energy you can get into the dry ice the quicker it will sublime into nothing. Something metal will conduct heat much quicker. It's something I've done in the past. If you get a metal spoon and squash a piece of dry ice then it sublimes much quicker and you get lots of gas given out with a high squeaking noise.

Would the genes be different for dark and light moths?

We put this question to Dr Remy Ware:Remy - That's a great question. Indeed this crucial genotype-phenotype link is what we are after really in evolutionary genetics. As yet we haven't really looked in much detail at the genome of the Peppered Moth but what is quite comforting is that we have very good sequence data from related Lepidoptera species, such as the commercial silk worm Bombyx mori and also some of the papillary butterflies. Their genomes are quite well-studied and it's possible that we can look for candidate genes within those and transfer it. A similar approach has been used in another species which shows melanism. The rock pocket mouse which is a lovely little thing found in North America and you have a melanic variety of this mouse which rests on a dark surface produced by larval flow compared to the normal form which is a sort of fawn colour. This species they've actually found the gene responsible for this polymorphism. They've found the gene responsible for the melanism which is due to the melanocortin 1 receptor gene. It's this particular gene that's mutated in that form of mice. That's an example where we do have this link between the genotype and phenotype. That's rather often used as a criticism of the Peppered Moth case in that it's lacking. The concept of being able to identify what's going on genetically is really exciting. Ben - If I'm right genotype is what the genes actually show you and phenotype is what we see on the outside. Phenotype would be the fact that it is a dark mouse. Remy - Yes so a phenotype is produced both by the action of genes and the action of the environment. The phenotype is sort of the physical manifestation of different factors causing a particular trait. They are genetics and environmental factors.

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