[SOUND] [MUSIC] So, I'm Nigel Goldenfeld, and I'm a theoretical physicist at the University of Illinois at Urbana-Champaign. So, you're familiar with the idea of a family tree. You have a familiar tree. Your parents gave birth to you. You give birth to your children. Everybody's descended from everybody else, and you can build that up into a tree structure. So, that idea is a one that is persuasive in biology. And the question that I want to talk about in today's lecture is not your family tree or my family tree but the family tree of all life on earth. And you may think well how could we possibly know the family tree of all life on earth, but amazingly we actually do know it. It was actually determined right here at the University of Illinois at Urbana–Champaign about 30 or so years ago, and it was determined by Carl Woese who was a professor of microbiology and one of my colleagues at the Institute for Universal Biology. So, I want to tell you about how we know the history of life on Earth. And then what that knowledge has told us about the structure of life, and how it could've arisen. And how it may have arisen elsewhere in the universe. And this is a, a very surprising story and is a story that is still being written. Because we don't know all the answers, and in fact we're going to see that trying to understand the history of life is like using a telescope to look back into the furthest reaches of time. So, let's start of with the history of life on earth. So, how do we try to explore that question? So Carl Woese's idea was very simple. He said look if I'm going to study life on Earth, I need to have some kind of barcode, some kind of measure of every single organism. Something that I can be guaranteed to find in every living cell. So, what do cells do? Well, cells reproduce, they metabolize, they do various functions in the body, but one of the things that they have to do, is they have to reproduce, and they have to also learn what they're supposed to do from their genome, from the genome of the cell. So, the cell has a number of basic functions then. So just to summarize a cell starts off with it's DNA. Ultimately the cell functions by making proteins. To make proteins it has to read the instruction set that is written down in the DNA. And, to do that, it first of all transcribes the DNA into messenger RNA. The messenger RNA is then processed by a machine called the ribosome, and that ribosome is the thing that takes the amino acid, the basic building blocks of life, strings them together to form every protein that makes up you. So, Woese's reason was very simple. Every cell must have a ribosome in order to function. This ribosome is fundamental to every living cell. And so therefore, if we want to understand the history of the cell, we should look at the history of the ribosome. We should look at the history of this translational machinery, and from that we can learn something about how cells evolved. So to do that what he started doing back in the 1960's was to start to look at the molecular sequences that encode the parts of the ribosome. Now the ribosome is an incredibly complicated machine. It has a lot of proteins, it has ribosomal RNA. And for various reasons, Rose decided to focus on the ribosomal RNA. And what he did, was he found a way, using what's called Sanger sequencing, a very difficult and time consuming, and in fact dangerous experimental technique, to find the molecular sequences of parts of the ribosomal RNA. And then what he did laboriously was to find the molecular sequences for as many organisms as he could get into his laboratory and then look at the results. Now, here's the idea of how you can take that sort of data set and turn it into an evolutionary history. So the idea is this, do you have a molecular sequence? That molecular sequence is different from organism to organism. It is different for the bacteria E coli than it is for humans. It is different between humans and from corn and so on and so forth. And by looking at the small differences between the molecular sequences, you can sort of say well, these ones are different here and different there. Maybe they're different, because there was a mutation and that turned this one into that one. And so by various statistical techniques, you can try to find out the most likely evolutionary path of these molecular sequences. And that's what Woese started to do, and by 1977 he had enough data to actually publish the first results of that. Now the first results were very surprising. Prior to Woese's work, it was thought that there were really just two kinds of life. Eukaryotes and prokaryotes. Now, what is a eukaryote? Well, you are eukaryote and plants are eukaryotes. In fact, eukaryotes are simply cells that have a nucleus to them, a nucleus where the DNA matter is stored, the chromosomes. The other sorts of cells are single celled organisms like bacteria round blobby things that you can see under a microscope. And those were called prokaryotes, because the idea was that they're simpler than eukaryotes, and perhaps they preceeded the eukaryotes in the timeline of evolution. So, that was the basic idea. Well, that turned out to be completely false. Woese blew that out of the water, because what he discovered was that, in fact, life could be split up into three types, not two. And it wasn't just that they were three different types, but he could infer their evolutionary relationship. So, what he discovered is shown in the phylogenetic tree, and that phylogenetic tree has got three branches of the domains, three branches or the domains of life, as they're sometimes known. The eukaryote, the bacteria, and the archaea. If you look at the eukaryotes, they include the usual suspects. But if you look at the bacteria and the archaea, they both look like round blobby things under a microscope. But they're as genetically different from each other as you are from bacteria. They're completely distinct. And furthermore, you will see from that tree, that the archaea and the eukarya, which includes you, have themselves a common ancestor. And then that branch itself meets with the bacteria at an earlier point in time. >> And there you'll find it in terms of this, and this, and this, all of which were trivial characteristics. And the only one that came through at the end was the prokaryotic cell wall, and this prokaryotic wall even collapsed when the archaes were discovered, and the wall structure was determined. >> So, that was the big suppliers then. But, there were three domains of life, and it's not that the single celled organisms were less complex then the multicellular eukaryotes. They are, but they evolved simultaneously with them over evolutionary time. So, they're not like an earlier stage and then life blossomed into its fullest form. [MUSIC]
