Science Book Club Episode 2
In a sense it’s the prequel and the sequel to evolution.
On the first half of the book
My background is evolution and genetics but I figured all of the best books about those two subjects have already been written, so what I decided to do was to remove the 4 billion years of evolution that we all know about and talk about what came before and what came after. So, in a sense, it’s the prequel and the sequel to evolution.
So, the first half is the about the origin of life: everything that comes up to the point where evolution begins. And that’s really a tale starting with the discovery of the cell in the 17th century and the subsequent discoveries of evolution by natural selection and cell theory and then, in the 20th century, genetics and DNA and all that stuff because what that has enabled is by moving forward through time we’ve begun to understand the roots of the tree of life. So you take this grand tree of life which Darwin first sketched in 1837 but now we’ve got two million species named on it, right, and you follow the roots back, on every branch, back all the way and you end up with a single entity. There is a single root at the base of the tree of life. Now we think that thing existed about 3.9 billion years ago and we call it LUCA, because it stands for Last Universal Common Ancestor, and all of the mechanics of cells, the genetics of cells, we think existed in that thing. The book is about how we get from chemistry to biology and the conclusion of biology, well the beginning of biology really, being this thing called LUCA. And it’s unexplained, it’s a…there isn’t an answer. There’s a lot of theories, um, there’s been a lot of talk over the past century about primordial soup and panspermia, which is the idea that life didn’t begin on Earth but it was delivered to Earth, either by comets or meteorites or by extraterrestrial intelligence. It’s a fun idea; it doesn’t have any basis in fact, so it has to stop with just being a fun idea and not being a scientific idea.
Primordial soup is the one that most people talk about, which is the idea that, if you get the ingredients right, if you can put together simple molecules that will react and turn into more complex molecules and eventually biomolecules, molecules that we see in our cells, then that would be the origin of life. Now Darwin speculated about this, there’s been some iconic experiments over the years about this: 60 years ago, Stanley Miller’s experiment was all about that. It’s wrong. It can’t be right. It’s, ah, it’s a problem of thermodynamics. Once that reaction has taken place, you mix it all together, throw in a bolt of lightning, as might have happened on the early Earth, as soon as that’s happened the reaction has reacted. It has finished reacting. So the problem with soup is that as soon as you take it off the heat it will go cold and that is not what life forms do. They maintain the harnessing of energy throughout the existence of a cell’s life, the existence of an organism’s life, and in fact continuously for the existence of all life on Earth. So we have to look for the signatures in an environment where you might see the type of biochemistry that is part of the energy harnessing process. And we’ve got a good model for that which is deep sea hydrothermal_vents. Alkali. ‘White Smokers’, they’re called.
Observation’s part of science; experimentation’s the second bit. Those experiments are being done about fifty yards from where we’re sitting right now at UCL and we await those results. To my mind, the argument in the first half of the book is that this is the best model we have for describing what life does.
So there are three grand unifying theories of biology, right? Physicists have been trying to come up with a grand unifying theory for physics to describe everything in the universe, they’ve been trying to do that for centuries and systematically failed. But in biology we’ve done it three times in the space of about 100 years.
The first is cell theory: all life is made up of cells and cells can only come from other cells. The second’s evolution by natural selection: descent with modification. And the third is genetics: that the code, the instructions to make every life form, every cell that has ever existed, is encoded in this universal language that we know as DNA. Now if you think about… something that we don’t…we don’t think about cells as often as we think about genes but every single cell in your body was born when an existing cell divided in two, right? So, for example, I got a little cut on my finger here which I got from playing cricket a couple of nights ago and it’s patching itself up, right, and it’s patching itself up with new cells. So those cells are born from existing cells and the cells that it was born from, they are born from existing cells already. As a cell goes from one and divides into two and you can trace that pathway back all through my life until you get to a point which is my first cell which is a fertilised egg, when I was a one cell thing. And then you can do exactly the same process via my father or mother. That sperm was one cell that was divided from another one all the way back to when he was a single cell. And you can keep doing that. You can keep doing that for every human that’s ever existed and for every hominid that’s ever existed and for every mammal that’s ever existed and everything on the tree of life consists of cells that have divided from pre-existing ones and that pathway traces all the way back through every species that has ever existed, right back 4 billion years to about 3.9 billion years ago to the very origin of life and I think that is an immensely powerful idea. That it doesn’t matter if you’re a bacteria or a sperm whale or a human or, you know, a mushroom or a flower, every single one of those organisms is made of cells that have a direct lineage all the way back to the origin of life itself.
Next month Adam discusses Part Two of his book: the future of life.