So we have groups that we can identify and say this is an insect. Now, organisms overall exist in these discrete clusters. So we don't expect a crocodile and a duck to get together and make a crocoduck. We don't expect these intermediates between modern day forms. Now, again we've talked about this way back when we've talked about evidence for evolution. So you don't see these intermediates between modern day forms. So what we have happens is we have to have these branches but additionally species have to form and make these new lineage without actually going back. So you wouldn't have an instructory you just have another comb jelly. But what would happen if there was never any branching? What would happen if there was no new lineage formation? Well instead of tree of life we'd have something much more like the twig of life. There are probably some branches that died off in there. Higher on the tree, up to here is the modern day. ![]() Where lower on this tree is long, long ago. We see later crabs and starfish and humans are reasonably close related. ![]() We have our various worms, that would be a C.elegans worm. We have a later branch off after we have the evolution of true tissues to these comb jellies. But as you see here you have multicellular ancestor and then long after this multicellular ancestor within the animal lineage we have this early branch off to the sponges. I have here just a couple of examples of animal life, obviously we can do this with all life and include fungi and plants and things like that. Now, this lineage formation is what leads to the diversity of life that we see on the planet. One lineage leading to the modern donkey. But over time we had these splits into one lineage leading up to the modern horse. That again horses, zebras and donkeys shared a common ancestor very long ago. Well partly, we've sorta ignored up until now, is this idea of formation of new lineages. This sort of change within the lineage, natural selection within a lineage, within a population, etc. This is what most of the class has been focusing on so far. And over time and leading to the present day, we see the modern horse on the order of a meter and a half tall. So we have these horse ancestors or at least contemporaries of horse ancestors that were half a meter tall. What are the two fundamental processes of evolution? Well, one of them as we described it is this idea of change within lineage, that over time, we have this set of ancient forms that lead up to the modern form. Let's start by going back a step to something we talked about way back in the beginning of this class. And indeed in one of the later videos you'll actually see a little bit of the research that I did. This is an area very near and dear to my heart because this is an area where in fact, I've conducted quite a bit of research myself. ![]() Today, we'll be starting to look at the process of species formation which is also just called speciation. Hello and welcome back to Introduction to Genetics and Evolution.
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