Convergent and Divergent Evolution

by Jason Amores Sumpter
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so we can see these evolutionary processes happening during the course of human history. But human history is just a tiny speck in the range of geologic time. So how do we know about all the evolutionary changes that occurred before us? Well, the fossil record is a great place to start in. The fossil record is simply all the fossils found on Earth. And, of course, fossils are formed when organic tissues are mineralized or become inorganic and makes them stick around a lot longer. And this provides ah lot of evolution Evidence for evolution. Uh, we already talked about radio metric dating at the very beginning, which is how the age of fossils is determined. If you don't remember how that works, go back and watch the very first video, which covers that idea now. Fossils not on Lee can reveal the relationships between species. They also can show us extinct species or species that are no longer live like this. T. Rex right here. Now some species that have fossil remains air actually extent or still living, So just because there are fossils of a particular organism doesn't mean it's not around anymore. In fact, the very oldest fossils that humans have uncovered called stromatolites. These air basically fossils of, ah, particular type of bacteria. Well, those bacteria still alive and well today you confined living stromatolites on earth today, and you can find fossils of them that date back over a billion years. So this is a really long time scale. How do we think about things that far back in the past? Well, we use something called the geologic time scale. This is a measurement of time that relies on geologic data. Issue might notice this girl standing in front of this rock formation. This rock formation has all these layers in it. We call those strata, and geologists use these various strata to develop or they have used it to develop a geologic time scale. Now let's talk about what those fossils can be useful for. For one thing, we can compare fossils from extinct species to those of living species or other extinct species and see the relationship in the structures now. Occasionally you will have something called convergent evolution, and this is the independent evolution of similar features. For example, the eye has evolved separately over 16 times in the course of life on Earth. That's a lot. Another example would be the analogous wing structure that we see right here. So analogous structures have similar functions but independent origins. This phenomenon is also called Homo Place, and we'll talk about that when we talk about file A genetics. So right here you see these different wing structures on the top. We have a pterosaur that's a type of kind of like a type of dinosaur, and below it right here. That's a bat right. That's a type of mammal, and below that is a bird. And remember, birds are close ancestors to dinosaurs, so the wing has developed multiple times, and the wings between these different organisms is an example of an analogous structure and convergent evolution, the independent evolution of similar features. Now you can also have divergent evolution, where differences accumulate between groups leading to the formation of new species, and these will likely result in homologous structures which have shared ancestry or home ology but now look different and serve different purposes. And we have some great examples of this right here. You can see all the bones have been color coded between the human arm and hand the dogleg bird wing and this whale flipper. Well, guess what? These are all homologous structures. They have shared ancestry, but they've developed differently. There has been divergent evolution, which has caused them to look very differently today. But you can see that there is Hamal Aji between these structures because basically, it's just the size and shape of the bones that's changed. But all the same bones are more or less there. Now let's flip the page and talk about some mawr evolutionary phenomenon.