 One of the things that scientists have been really curious about is this branch point here. How are the eukaryota related to the archaea related to the bacteria? If you remember, the earlier divisions had the eukaryotes separate from the prokaryotes over here because of those morphological differences. But the eukaryotes have a lot of commonalities with the archaea, which is why this branch point was placed here. So these trees down here are drawn a little bit differently with sort of this horizontal bars representing different things. So this tree is actually the same as this one. In terms of the information shown, I'll just show one represents the one here. The the branch over here, it represents the one that goes to the bacteria. The branch over here, branch three, is right here. And then four is this one right here and five is this one right here. So what really matters is the order of branching and not necessarily how it's drawn. So this tree is the same as the one up here. You have the common ancestor and then you have the branch point going to the archaea and the eukaryotes versus the bacteria. Then you have a branch point between the archaea and the eukaryotes. But the similarity, when scientists started looking at more genes beyond just the ribosomal genes or ribosomal RNA that woes looked at, they started to think that the eukaryotes actually might be descendants from the archaea. So what this means is that the archaea evolved and started to differentiate before the eukaryotes came about. Okay, so what I've done out here, an example that might be more familiar. We have crocodiles, dinosaurs and birds and for a long time it was thought that the birds and the dinosaurs diverged from a common ancestor, but that the birds weren't actually from within the dinosaurs. With more and better fossil record, we've learned actually that we don't have the birds sitting here as a branch of the dinosaurs. We actually have some dinosaurs here and then there's another branch here, which has other dinosaurs and the birds branched off here. And so the difference between these models is that some dinosaurs and the birds did diverge from each other at this point right here, but the last, the common ancestor of these dinosaurs and these dinosaurs and the birds was also classified as a dinosaur. All right, so the birds actually emerged from within a lineage that we classify as dinosaurs. So if we look at that relationship here, what this means is that the animals, the dinosaurs and birds and us, all emerge from within a group of the archaea. And this is a very novel and controversial proposal that is still being very highly debated within the science community. And that's because the the cell structure is so different between the archaea and the eukaryote. So these four diagrams represent change in the understanding of evolutionary relationships in the last few years, according to a group of scientists who think that the eukaryotes emerge from within the archaea. Again, this is this is still controversial because of the huge differences in the cells. But this is, this tree is sort of the first one and the interpretation is that you have two different types of archaea here that are separate from the eukaryotes and the bacteria. So this is like the original tree from Wallace that we first looked at where the eukaryotes are separate from these. With more genetic analyses, a lot of scientists thinks that the eukaryotes emerge from within the archaea. So these two branches here represent the archaea and the eukaryotes are within them. Then with more genetic analyses, these Cren archaeota became divided into more and more branches. And you notice here this model shows the eukaryotes and these various different types of archaea all coming together. And you see the eukaryotes emerging out from the same place. When you end up with lots of things emerging from one place, it means that the genetic data that you're using to create your model don't have enough details to resolve what actually happens. And so this is a very similar geometry to be here except that data used for the model says this is a really interesting confusing point that we need more data for. And then the most recent version basically actually separated out all these blue lineages into some more. And there was a new group of archaea identified. Here that is thought to be most closely related to the eukaryotes. So now if we look at sort of all the archaea, you have this this huge range of them. And the the eukaryotes are just a small in essence leaf on the archaeal tree. Right. So I'm going to reiterate that this is still controversial. And and it's one of the really interesting things in terms of trying to understand the evolution of life is how the eukaryotes might have emerged from the archaea or whether that this is not the right model and one more like woes originally proposed is the correct one. But in that case, why are there so many genes in the eukaryotes that that allow this tree to be developed that suggests that the eukaryotes are just are emerged from within the archaea. So there's disagreement about where the eukaryotes fit within the phylogenetic tree and in this version these leaves on the tree represent large groups of organisms. The branching points are the same and the archaea are on the right side. The bacteria or eubacteria are on the left side. And this one has eukaryotes in between and not actually branching off the tree here. In this particular case the idea is that lateral gene transfer among organisms is really important for the creation of the eukaryotes. Rather than being descendant from a lineage of organisms, they represent a genetic merging of different organisms. And so in this model there's the branch of archaea here that some or archaea organism here merged with an organism from the bacterial tree of life to actually create a new organism. So this is like a form of super symbiosis. In the sense that we have this merger of two or more very different cell types. And then it's a merger of these that was the common ancestor for eukaryotes. And there is some evidence that this happened in other cases as well because we have both the mitochondria and the chloropeloplast. Both the mitochondria and the chloroplasts have DNA within them. They're the organelles within the eukaryotic cells. And that when we put the DNA in these organelles back into a tree of life, they come out as being within the bacterial tree. The chloroplasts evolved from a cyanobacteria and the mitochondria evolved from a bacteria that had oxygen respiration. So this is yet another model for how eukaryotes evolved. And one of the really interesting things about science and tracing the evolution of life is that we've we use the data that we have to make the best model and then we challenge that model by trying to collect new data to prove or disprove it. And as we're doing that with the genetics the relationships among organisms are becoming clearer but it's also showing that the processes and the relatedness of organisms is much more complicated. Then much more complicated than our earlier models understood.