Amy Barrett: Hello and welcome back to the ‘Everything you wanted to know about’ podcast from the team behind BBC Science Focus magazine.
I’m joined by Sir Paul Nurse for the second and final part of our series on biology. Last time we talked cells, DNA and genes, and today we’ll be linking these concepts to mutations, evolution, Charles Darwin and even the poetry of his grandfather, Erasmus.
So, in the last episode you explained to us how genes are the basis of heredity. But, how do genes get passed on?
Sir Paul Nurse: So, heredity is central to life. Every time a cell reproduces itself, it copies its genes, the basis of heredity, and what those genes do is essentially encode the information that cells need to grow, divide, reproduce.
That information is also the basis for our cells. We’re made up of many, many cells, of course, but when we reproduce, we reproduce through a single cell. So, we receive those genes through the sperm, which is one cell, and the egg, which is another, that come together. And it is through heredity that we get evolution by natural selection.
So, let me just sort of describe that very briefly. This is Charles Darwin’s great idea, and it works like works like this, really. I’m going to talk about it, not in terms of human beings or plants and so on, but back to cells. The cells show it in its simplest form.
Imagine you’ve got cells and growing and reproducing. And let’s imagine they’ve got, say, a red coat. And let’s say that the red coat, it’s very attractive to a predator like eating cells which are red. OK, so now that red coat is caused by a gene which says ‘have a red coat ‘and let’s now imagine a mutation occurs in that gene. So, the coat is blue now.
Maybe if you’re a blue cell, your predator doesn’t like to eat. It doesn’t like the look of you. OK, so if you now have a mutation that makes the blue cell, that won’t be eaten and so that survives and divides much more efficiently than a red cell.
So, you’ve turned to red cell into a blue cell and that and that blue cell works better because it doesn’t get eaten by something else. And that’s a very simple example of evolution by natural selection. And if you imagine that happening in far more complicated situations like our reproduction, then you can see how you acquire properties which have a purpose, that help you live better entirely without planning, just by accident.
That’s the beauty of this idea. You don’t need a creator or a designer. It just happens that the variation the hereditary brings about is selected for, variation that actually works and is more effective at allowing the cells or the organisms to grow and reproduce. And so you get operation as a whole through this very random process. And it’s a way of getting function and things working without having them being designed.
AB: So, if mutations are key to it, how does a mutation actually happen?
PN: Yes, it’s a good question. Mutations happen in a variety of ways. The first way is that because genes are made up of these bases, AGCT, they have to be copied precisely every time they are replicated or doubled. But occasionally there will be a mistake. So you might change an A into a G, for example, and then you have a mutation. So it occurs naturally just because of a low level of error in the way you copy DNA. It can also occur, mutations, if you have a DNA damaging agent.
Sunlight has got UV and that can damage the DNA in your cells and that can cause mutations, which is why certain cancers are caused by sunlight because they damage the gene is important for controlling the division of cells and that can lead to cancer. DNA damage can be caused by UV light or by chemicals.
So, there’s two main ways of doing it. One is just normal process of making a bit of a mistake when you copy the DNA, the other is an external effect, like radiation or a chemical.
AB: But not all mutations will lead to an aspect of the evolution of a cell.
PN: No, that’s true, too. It’s entirely random. So some mutations will just destroy the gene and kill the cell or kill the organism. Others will change the way it works.
In the example I used of a red coated cell becoming a blue coated cell, it changes it from red to blue and that may have consequences. Often the consequences don’t help the cell or the organism very much. And just occasionally it does and it makes it work better. And then that’s what it’s selected for during evolution.
AB: So evolution and natural selection are not the same thing, is that right?
PN: Evolution by natural selection. Evolution is the change, the change of an organism and eventually a species. Natural selection is because you select naturally like, uh, animals in the African plain who can run fast, that can run away from lion, for example, and that’s natural selection. But actually we can also use artificial selection, human beings.
This is the way that Darwin started to think about this, because you know that people who breed pigeons, pigeon fanciers and you get lots of different types of pigeons. And Charles Darwin used to go and talk to the pigeon fanciers and breeders.
Let’s say they wanted a pigeon with a big tail. They would select pigeons with big tails and mate them together. This was artificially selecting who should mate with who. So, you get bigger tails and that’s pigeon fancying.
But actually, that’s been really important. The agricultural revolution ten thousand years ago when we got wheat and barley and rice and so on, was because our ancestors noticed that certain plants they saw in the wild had bigger seeds and then selected them, crossed them together and gradually selected new plants that actually we could now turn into agriculture.
So, the whole basis of agriculture depends upon evolution by artificial selection. That’s why we can now feed so many more people today than we could have done when we were Stone Age peoples.
AB: So that seems to have happened quite quickly.
PN: Artificial selection can work much more quickly than natural selection because you select what you want. And so the agricultural revolution, I mean, it worked over several thousands of years. It just gradually got better and better.
But even so, in evolutionary terms, that’s a very short time. And pigeon fanciers, of course, can do really rather quickly because you see the whole range of different pigeons, dog fanciers is another one.
I mean, look at the immense range of different dogs from, you know, a little poodle through to the Great Dane. And that’s the all produced from dogs, which came from wolves originally, and they’ve been selected for different purposes to look right, to run fast, to hunt. And so we’ve got a whole range of different dogs which have been produced by artificial selection.
AB: You’ve mentioned Charles Darwin and he was really key to all of our understanding about evolution and natural selection.
PN: He was a 19th century biologist. He was quite a comfortable, well off man. So, he was an amateur scientist because he could afford just to live on his inheritance. And he lived in Kent, actually.
He was famous because he went on a long voyage around the world in a Royal Naval ship called HMS Beagle. And there he collected lots of plants and animals and studied them in the wild. And that’s where he got his ideas from. But he wasn’t the first to suggest evolution, but he was very important to suggest the idea of evolution by natural selection and evolution, that is, that the animals and plants can change, had been talked about for a hundred years before, including by Charles Darwin’s grandfather, who was a very interesting character called Erasmus Darwin, who lived in Litchfield and then in Derby.
He’s a fascinating character. He was a doctor, he wrote all his signs up in the form of poetry. I’ve got some of his original books. So it’s all verse. It’s very entertaining or fairly entertaining to read it. And he was a doctor. He only charged rich patients because he treated more patients because they couldn’t afford it. And he was a very good doctor, but largely because he was.
He had one very good skill, he could tell you what you were likely to die or not. And that meant that if you were ill, you can put your things in order. But if you are going to recover, then you didn’t have to put them in order. And that might have been quite important. You might upset people with a different sort of will, I suppose. So he was he was very good at that. He was a Republican. He was asked to be, I believe, the doctor of George the third, which I think he refused to do. He was interested in all sorts of things.
He belonged to a society called the Lunar Society. This was a scientific society that met in the Midlands and nothing to do with universities or anything. It had people like Wedgwood, who was the potter, and Erasmus Darwin and so on, and they used to meet once a month under the full moon, which is why they were called the Lunar Society. And they had a good dinner. I suspect they drank quite a lot of good wine and then they rode home under the full moon after that.
AB: Is that still a society today, do you know?
PN: It still is. It sort of comes and goes. And I have actually spoken at the Lunar Society and I think probably more than once. I’m not sure it’s active at the moment, but it’s definitely been active during my lifetime.
AB: That’s amazing. Um, your book is called What is Life?. And it wouldn’t be right of me to do this interview without asking you, what is life?
PN: Well, I’ll have a go at answering it. I have to say, it’s quite difficult. It’s very easy to ask. It’s not quite so easy to answer. And it’s a bit complicated because you can’t answer it like a dictionary, you know, there isn’t one sentence that defines it.
But what you can do is take the five ideas and that I talk about in my book and sort of boil them down to several principles. And the first is to describe living things.
Living things are chemical and informational machines based on cells, and that allows them to make themselves, to maintain themselves, and to reproduce themselves. So that’s the first principle.
The second one is that they have a hereditary system based on genes and genes are found in all cells, of course, and these genes are handed down through the generations.
Now, if you had a living thing which has those properties, then that allows them to evolve by natural selection, because if the genes exhibit variability, then they can evolve by natural selection and acquire purposeful behaviours. They acquire purpose.
And so that allows life, which is a physical thing, to actually get functions and processes that leave acting as a whole as purposeful behaviours. On our planet, life is based upon DNA, RNA, that DNA makes and also proteins. And we haven’t talked about this yet. But all of these are chemical polymers.
That is, just as DNA is made of AGC and T. RNA has got similar bases. Proteins have got 20 letters. And the DNA encode proteins with a particular sequence. And it’s the proteins that actually do most of the chemistry of life. So, we – our life, all of us from bacteria to us is based on that chemistry.
Now, I don’t know what life looks like elsewhere. Nobody does. We’ve been hearing recently about life forms maybe in the atmosphere of Venus. We don’t know what it might look like, but I have a hunch that it will probably also be based on polymers because polymers can encode information. You know, if you take a computer, it’s lots of bytes, bits. If you read a sentence, each word is made up of letters. If you hear both of us talk, we are talking with letters. All of this is digital, really its chains. Polymer chemistry is also a chain. So, what you get with a chemical polymer, it’s chemistry that can do chemical reactions, but it also can encode information as well. And that is very special.
AB: What kind of information could it possibly encode?
PN: Well, if you think a protein is does chemistry and that depends on having amino acids, which is what makes up proteins, in a certain order in a chain and with certain chemistry, they might have positive charge or negative charge, they might like water or not like water. There’s all different chemical properties which and that determines what they can do and what they can do is determined by the DNA and the sequence of the nucleotides that make it.
So, it’s an amazing system where you have both information encoded. It’s an informational machine and that encodes chemistry and it’s a chemistry machine. So what I was going to say is I don’t know what the chemistry of life will be on, you know, Neptune or wherever or Venus maybe. But I’m pretty certain that it will be based on polymers.
AB: And all of this research you’ve done, you’ve talked about working with yeast for a long time in your career, where did the fascination with biology cells and life for you come from?
PN: Well, I’ve always been interested in living things. And I sort of remember once when I was I think just a teenager and I was sitting in my garden, which was in north west London, in Wembley, where the stadium is. And a yellow butterfly flew over the fence. It was a brimstone yellow. It was early spring. They come out in March.
And I watched the yellow butterfly, it flitted about and it settled on a flower, had a little feed I think. And then I think I disturbed it and it flew up and it went over the other fence going the other way. And I remember thinking, you know, this is butterfly. It’s really a bit like me. But it’s also obviously very different. So, what is the same about a yellow butterfly, brimstone yellow and me? And I think that was the start of me thinking about biology, to be quite honest. And then, of course, I was taught it at school, but it was just looking at living things and thinking, what is the basis of that and how is it like me, and how is it different?
And my book goes into this ,that it’s amazing really – because of evolution, by natural selection, we’re related to every living thing on this planet. So, that butterfly is sort of my relative. And, you know, if you think more profoundly about that, you think, well, we have a responsibility to look after our relatives and we need to care for the biosphere, for all the living things you find there, because we’re related to them.
And not only that, but actually we depend on them too. All the food we eat, the plants and animals and fish. If we didn’t have them, we couldn’t survive. And the natural environment around us is so enriched by animals and plants, insects and so on, and we interact very closely with all living things.
So we’re all connected, connected because we’re related to each other, connected because we’re dependent upon each other. And that’s why it’s so important that we maintain the biosphere and other lifeforms we have a responsibility for them. It is our responsibility. That’s how I in my book, actually I say we have a responsibility for all life. And what I tried to do with the book is to explain what life is, so we care better for life.
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