Charles Darwin’s theory of natural selection did more than explain evolution, it revealed how complexity can emerge without a designer. Nobel laureate Paul Nurse unpacks Darwin’s insights, from the logic of tiny differences to the profound impacts these variations have on our understanding of life.

Nurse explores the deep genetic connections linking all organisms, from humans to gorillas to yeast. This shared ancestry, he argues, reframes how we think about responsibility: If all life is related, what do we owe to the living world?

PAUL NURSE: There's two things we have to think about here. One is evolution itself. Do animals and plants evolve? And the second is, what is the mechanism by which it takes place? The idea that animals and plants might evolve is actually quite old. Even Aristotle had some thoughts about it. But particularly in the 18th century, there were a number of people who speculated looking at fossils and so on that animals and plants had evolved over time. But it took Charles Darwin in the middle of the 19th century to come up with a mechanism, evolution by natural selection. And he came to this position because of a five-year voyage he took in a small royal naval boat called the Beagle that went around the world, and he collected animals and plants and birds and studied the geology, made lots of natural history observations. And this eventually led in the 1840s to his idea. He didn't publish it till 1865. And it provided a mechanism by which animals and plants could evolve. And really, you could get design without having a designer. Now, how is that possible? It's a very clever idea, and it's based on the genes that I've already talked about, and cells really. And what he speculated was that all living things have hereditary material. He didn't know about genes, but he speculated that they had hereditary material. That if this hereditary material had some differences that resulted in the living thing, living organism being different, then it is possible that what was produced was perhaps a plant or an animal that could grow faster or produce more offspring. And that would mean that in the next generation, there would be more of that particular variant. And if it was advantageous in the environment in which it found itself, then that it would eventually take over the whole population. So you get a change from one type of organism into one that was a bit different. I sometimes think of a very simple model just to explain that. Imagine a single-celled organism which had a red coat outside the cell, or a yellow coat. Let's say that the red coat got eaten by some other living organism. Then if there was a mutation which resulted in the red coat turning into a yellow coat, then the yellow-coated cells would survive better than the red-coated ones. And as a consequence, they would take over the population. And that's just a very simple example of evolution by natural selection. But it's also built on the ideas that I've been talking about. It's built on the idea of genes and the fact that genes determine the properties of cells. And if you have genes determining the properties of cells and the genes show some variability, then you will simply get evolution by natural selection. And this was the idea Darwin had. He didn't know about genes, but he did know about hereditary material. And this has been a revolutionary change in our understanding in biology because what it leads to is a better-designed living thing without having a designer. It can occur just randomly by selecting naturally for those changes that are more advantageous for that living thing. It really truly is a beautiful idea. One of the consequences of evolution is that we're related by descent, because if we all can trace back our ancestors to a common place, then every living thing on this planet is related. And this is rather profound, really. The relatedness of all living things, and particularly of humans to other life forms was brought home to me in a very special way, almost spiritual, when I was trekking through a Uganda rainforest looking for gorillas. And we came across a whole family of them, 20, 25 of them. I sat down behind a tree. I was a little bit separate from the rest of my group. And then this very large male gorilla sat down in front of me and looked at me, deep brown eyes. He put out his arm, he bent down a sapling tree, 2, 3, 4 inches in diameter. I'm sure he was telling me, you know, "I can do this. I'm not sure you can do this." But sitting there, just looking at him, seeing the similarities, his deep brown eyes, and they were really staring at me, it just looked like we were having a conversation somehow. He sat and looked at me for a while, then he climbed up the tree, and then he peed all over me. So I don't really know whether he was trying to put me in my place, but for sure, it was a magnificent interaction. Here I was, almost talking to a sort of relative diverged 5 million years ago, 10 million years ago, and it made me think of the deep connection between all life on this planet. It's just that we diverged further and further back. And that experiment that I described of taking the human gene and putting it into a yeast cell and showing that that human gene could control the reproduction of the yeast cell just as well as it could control a human cell, even though they diverged 1,500 million years ago, is another example of the extraordinary similarity between living things. And I think about this quite a lot because doesn't it mean if we are related to every living thing on the planet, do we not have a special responsibility for every living thing on this planet? They are really all our relatives. Do we not really have a responsibility to be a steward for all animals, plants, fungi? We have a responsibility for them. And it's the best argument I've seen in an abstract sort of way that we should take care of every living thing that we can on this planet because we're related to every living thing on the planet. They are our relatives.