Nobel prize-winning geneticist Sir Paul Nurse's latest book, What Is Life?, explores the question of what we as humans share with all other living things on this planet.
By identifying the five great ideas of biology that characterise living things, and turning them into principles that define life, he takes up the challenge of describing what it means to be alive in a way that every reader can understand.
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Nurse is one of the most honoured scientists alive; he is an English geneticist, former president of the Royal Society, director of the Francis Crick Institute, and has been awarded more than 60 honorary degrees and fellowships.
But he says defining life itself isn't a clear cut concept.
"I think it's still a question: how do we distinguish between something that's alive and something that is inanimate - has never been alive? And it is central to biology, and quite curiously we've never really had a satisfactory answer, so I thought I'd have a shot at dealing with that question.
"The way I addressed the problem was to identify the five great ideas of biology that characterise those ideas, and then take those great ideas and turn them into the principles that define life.
"And they are: the idea that the cell is the basic unit of life and all living things are made of cells; the second idea was the gene being the basis of heredity, which is a very special characteristic of living things, every time an organ reproduces it passes on genes from itself to its offspring.
"The third idea in life is chemistry; that is you can understand the processes of life in terms of chemistry. The fourth idea is life is information, that complex chemistry and physics all has to be linked together in a purposeful whole, and you can only really deliver that if you are managing information, communicating between the different chemical reactions so they start behaving with purpose.
"And then the fifth, and probably most famous idea in biology is that all life evolves by natural selection. And why that is important is because it's a way of living things acquiring purpose and excellent adaptation to their environment and how they live, without being designed.
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"Normally you'd think of objects with purpose, like a watch, because it's been designed to have that purpose. But evolution by natural selection delivers purpose without design."
Life has an operating system, as it were; it's a chemical, physical and informational machine.
Nurse says out of those crucial ideas that define life, cells are perhaps the most under-celebrated.
"There's been a lot of talk in popular books about genes, and heredity and the double-helix of DNA, but actually they only come to life - quite literally - in the cell.
"Cells are critical," he says. They range in size from the yolk of an egg - which is a complete cell in itself, to a bacteria small enough to line up 3000 of them across a 1mm gap.
"It is really wonderful that in a tiny, tiny little microcosm of a cell... you pack thousands of different chemical reactions all connected together, all leading to purposeful behaviours, all happening simultaneously all in this tiny confined little space.
"It's the most exotic complex chemistry that you could imagine, which can only be replicated by us humans most of the time in very complex and large chemical factories, really. And even then we get nowhere near the chemistry of life, and all that is contained in cells."
Proteins (including enzymes, a particularly active group of proteins) are crucial actors in the biochemistry of life, and exist because of biological digital storage.
"This is something that's really quite exciting," Nurse says.
"We tend to think that digital information storage devices were invented with the origins of computers, and the sharing of bytes of information stored as strings of zeros and ones, that have a sort of code that you can read. This is information storage, and it's being stored in a linear fashion in silicon, in the middle of a computer.
"But that is exactly the same mechanism which is storing information in our DNA, which is the basis of heredity. That has also got letters or numbers like zero or one, but there's four letters which are named after the bases that make up DNA... AGC and T.
"They are like the bytes of information... in a computer, or for that matter the order of letters that make up words, sentences, paragraphs and even books.
Human DNA Photo: PublicDomainPictures / CC0
"But the information can't do much, and the beauty of life is that the information stored in the DNA, chemically inert and stable, can be translated into... a sequence of amino acids, which are much more chemically diverse than the bases used to make up DNA.
"Those 20 amino acids can be arranged in a huge variety of different orders, creating many different structures that can fold up in different ways, and generate an enormous range of different chemistries."
Amino acids form the building blocks of proteins.
"Proteins... are fantastically complex chemical machines with huge chemical diversity that are doing work, they are not just inert storage devices, they do the chemical work that is determined by the information stored in the DNA."
A "fantastic advance" is CRISPR-Cas technology that allows manipulations in the DNA of living things, and opens many new possibilities, Nurse says.
"I think biology is going to be core to our future lives, the ability to manipulate and change living things allows us to think about ways that we can control disease, correct defects that we may have inherited from our parents perhaps, allow us to deal with degeneration of our nervous tissue or our muscle. All of this is very important, as is being able to grow crops more efficiently and effectively, get them resistant to fungi and other predators, and so on.
"But all these advances... sometimes people get challenged by them, that we're tinkering with nature, we're playing God. And this means that if we're going to use these techniques we've got to have proper discussions in society about what we should do, what the implications are of what we're doing.
"And these need to be decisions not made by scientists, but actually by society as a whole with good political leadership that will promote proper discussions. And that for me is going to be one of the big challenges of the coming years, to ensure we have proper discussions about the best use of science, to not only understand the world, but also to use it to improve the world and improve the way that humans beings can live in that world, but in ways that society finds acceptable.
"And that means discussing these issues early on, when discoveries are made, rather than letting them catch up on us and then trying to deal with them once the genie is out of the bottle."
