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Evolution: How do we know it exists?
Transcript of Evolution: How do we know it exists?
"A theory that the various types of animals and plants have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations; also : the process described by this theory." In other words: Evolution is how a species progressively changes, and eventually becomes a new species. The diversity of life on this planet is the result of evolution taking place over the course of Earth's history. I couldn't have said it better myself! This can been seen by looking at fossils of prehistoric animals and comparing them to either two modern day ones... Or a species predating it and a modern species. Evolution is always occuring, and every creature on Earth has resulted from it. All of Earth's vertabrates came from the early Cambrian protofish, Pikaia. See that thingy there? That's a notochord. The notochord was a flexible, but sturdy rod that ran through the pikaia's back, next to it's neural cord. Sound familiar? Well that's cause this notochord eventually became... ...This thingy! The spine and spinal cord, and even the brain! Look at any vertabrate today, that same stucture is still present. These are what are called homologous structures. Homologous structures are similarities within organisms that evolved from a common ancestor. We can see these in the forelimbs of most vertabrates. OMG NO ULNA!!! This would imply... That traits that are similiar in this fashion came from a common source. However-- Analogous Structures occur when a trait is favorable and as a result appear in multiple species. When this happens, we end up with multiple species with a common trait. On present day Earth, we have seen the gene for large, piercing teeth numerous times. The mammalian gorgonopsid had two huge canines for ripping flesh. The famous saber-tooth cat, or smilodon, had two huge fangs to pierce its prey's throat and cut off its breathing. Modern day male walruses have huge tusks which they use for bloody duels for mates. Scientists and artists even speculate such adaptions could arrise elsewhere, such as Earth's future or even another planet! The earthly snowstalker evolved from an animal from the weasle family, and uses its saber teeth to wound its favorite prey, shagrats, and follows them until they die of blood loss. The hermaphroditic "Unth" of Darwin IV uses its tusks to fight for mating rights. So, this means that if a feature is specialized enough, it can reoccur in organisms over and over again. In such situtations, it can be hard to tell if two creatures evolved from a common ancestor or if their common traits are simply coincidental. But in anycase, this only goes further to show how diverse the life on Earth really is. There are things called analogous structures in which two organisms have similar traits, but are not related. Now, some people would say that evolution does not exist, but in that case... How can such critics explain... THIS?! This is an image of a set of bones found in whales. They are the remanants of what were once legs. These legs have shriveled and atrophied over the course of eons, and eventually became unnessecary for the aquatic creatures. In the future, the whale's leg bones may disolve into nothing. This is an example of what we call vestigal structures. This is Ambulocetus, a mammal from the early Eocene.
This creature was amphibious, and looked a lot like a furry
crocodile. The Ambulocetus swam a lot like modern day whales
do, and preyed on small animals that came by the riverbank. As
you can see, it has two long legs in the back of it's body. These legs
eventually became less and less useful. These are two Basilosaurus, early predatory whales from the late Eoscene. That didn't take very long, eh? These huge whales were the apex predator of the seas in their time, feasting on animals both terrestrial and aquatic. In this image, we see two individuals engaging in mating. Notice the small remanants of the hind limbs. Scientists speculate that these interlocked during mating, that was all they were for. For anything else, these limbs were useless, and eventually they weren't even needed for mating, so they shrank back into the whale's flesh and have been devolving ever since. Now whales have only two flippers and a long fluked tail. Their vestigal pelvis and legs are hidden within their body, useless. This is an excellent representation of vestigal structures and how evolution eventually loses need of organs. This can be seen in many other animals, including humans. So all in all,Earth's diversity is thanks to evolution. Without evolution, we'd all probably be... THIS. One thing to know about evolution is that it Recycles. That's right. As in recycling adaptions. Think about it. Where did the bird's wing come from? The dinosaur's arm. But how in the world did THIS Become THIS?! How did a Running animal such as this... Turn into a flying animal like this? This man may have the answers. This is Kenneth Dial. He works in
the University of Montana Flight Labratory. In 2003, he proposed a new theory on how dinosaurs took to the air. He noticed that chukar partridges used their wings to actually run up vertical surfaces. Also, the animals seemed to be able to do this intinctually at birth! Here, watch! And it's not just the partridges! Look! Feathery dinosaur hatchlings might have scrambled up into trees to get away from predators. This seems like a very effective way of not getting eaten. One day, one little dinosaur must have run up juuust the right angle and.... FLIGHT! Scientists who worked on the documentary "The Future is Wild" say that such things could happen again. For instance, look at these little beauties. This is a Flish. Flish take flight one step further. Powerful muscles in their pectoral fins let the flish leave the water completely and take to the air. This may seem surreal, but it makes perfect sense. If there were a gene in flying fish that made them have the urge to flap their fins up and down while they glided away from predators, they would gain lift and have a better chance of escaping. If this became more common, large pectoral muscles would become favored, as well as the development of lungs, and voila! Fish that fly! Now, check out these beautiful creatures. To the left is an ophthalmosaurus, an ichthyosaur from the late Jurrassic. To the right is a slightly more familiar creature, a bottle-nose dolphin. One thing you'll notice about them is that they are analogous in shape; the shape they share is superb for moving swiftly through water, but what's most interesting about them is how they evolved. As we have discussed, cetaceans (dolphins and whales) evolved from a common land dwelling ancestor. The ichthyosaurs evolved in a similar fashion, their ancestors being traditional land reptiles. This is Utatsusaurus, one of the earliest of the ichthyosaurs. Does it look somewhat familiar? Utatsusaurus has a very similar shape to Ambulocetus, the ancestor of whales and dolphins. At the same time, there are a lot of differences. Ambulocetus has longer limbs and a much more profane neck. It's snout tapers much less than that of Utatsusaurus. This is what's called Parallel Evolution: When two organisms develop seperately and end up as extremely similar animals. But the main focus of this is the flipper of the two animals. If you look at this image, you will see the steady progression of the ichthyosaur fin. Like the dolphin, we see that earlier ancestors' legs were similar to the legs of their terrestrial ancestors. We see the same evolution in
dolphins, how the forlimbs
becomes a paddle... ... And the hind
limbs shrink into almost nothing. Sharks have a very similar body shape... Hey, were doing the flippy thing again! However, sharks have been evolving for four hundred million years, and they have never left the water in any of that time, but they have evolved some of the craziest adaptions in the past, present, and some speculate in the future. Now,let's look at giraffes... Okay, now let's talk about
giraffes. trollolololololololol Most people assume that since they have such long necks, giraffes have a lot of neck vertabrae, but as it would happen they have same number of vertabrae as humans; seven. The vertabrae are extremely stretched out, making the neck longer. Giraffes evolved from much smaller animals with compressed neck vertabrae that most likely browsed on shrubs or very short trees. Over time, a gene for longer neck vertabrae developed, and that was favored among the animals. Eventually, the shorter necked population died out, possibly because the shorter plants they dined on became too scarce. So rather than producing extra vertebrae, the giraffes simply modified it's current ones to be longer, just as the dolphins modified their feet to be flippers and dinosaurs used fluff to fly. Evolutionary recycling at it's finest. Now here's a nice big question: Can evolution be affected by outside forces? Can it be guided by events? Well, there's probably some huge mind boggling answer to this somewhere, but in short: YES. One way evolution can be affected is through variation. Natural variation is when mutations arise in a population, become favorable, and stick around in the population. One example of variation today is one you are very familiar with... YOU. Humans are incredibly diverse creatures. GABE NEWELL! Hair color, skin tone, eye color and shape, height, etc.! It's amazing! That's not human... In any case, all this variation gives us an advantage. Now this a bit extreme, but let's suppose aliens appear on Earth: A new organism to put a new circumstance into Earth's ecosystem. These aliens eat humans. But let's say they only eat tall humans. So these people get eaten... (Nothing personal, you taste good.) Where as these people survive! Yes, Lord of the Rings reference. Deal with it. Good news! We can still watch Pitt Boss! Or what if all the world's men contracted a deadly disease and died? Whiptailed Lizards have found a way to continue with out males; they clone themselves. (Though they still need a form of "stimulation" to reproduce.) Basically, women could evolve to clone themselves without men. Neat, huh? Could present some problems, though... Clones and aliens aside, this has happened. In fact, it's how most species form! See, natural selection, the driving force of evolution, only occurs within a population with variety. Favorable variations are selected, and those with these variations survive longer to produce more offspring with the same variation. Let's suppose we have two stags.One has small antlers, the other has much larger horns. It's the mating season, and the two stags must fight for a mate. Who do you think will get the mate? Ptthbbbt! Well, probably the stag with bigger horns. In turn, he passes his genetic code for big ol' antlers to his offspring and giving them a chance of having an advantage like his. If this is passed on more, it will eventually become much more common for male deer in the population to have bigger antlers. And all this happened because one deer had bigger antlers. Isn't variation awesome? Another driving force of evolution is finite resources. In case your not clear on what finite means, think about the word infinite; never ending, eternal, never running out. Finite is the opposite of this, so finite resources are those that can and will eventually run out. What is finite is really dependent on your line of thinking. For instance... Early man thought trees were an infinite resource,
but now we are pressured to protect out forests,
for they are in decline. The sun seems like it will last forever... But it will eventually explode in a cosmic event known as a super nova. Even time and space could run out eventually... Physics aside, for the sake of this presentation we shall define a finite resource as a resource that can be lost from the actions of a species or a natural event taking place on earth.
These include: food, water, climate, another species, shelter, or a habitat. Think back to our giraffes. We have our longer necked giraffes and our shorter necked giraffes. The shorter giraffes cannot reach tall trees, so they feed on shrubs, while giraffes with long necks eat delicious leaves from the tall trees. Now let's say all the shrubs died out, maybe in a freak forest fire. The trees are the only plants left, so the tall giraffes survive on them, but short giraffes eventually die off because they have nothing to eat. Something like this happened somewhere in giraffe evolution. Another influencial force to evolution is competition. Competition is a common driving force for a lot of things, it's found in our silly forms of entertainment. Watching sports, video games (Especially first person shooters. *COUGH COUGH* Call of Duty *COUGH*), and even simple board games. But it influences evolution quite a lot. For instance, check out the African savannah. Lions and Hyenas have been natural enemies for eons. The two will often fight over their recent kills, the hyenas with their powerful senses and bone crushing jaws, lions with their immense power and frightening roar. This feud is caused not by a long time grudge, but by competition. Competition occurs when two species need the same resource. This will often result in an evolutionary arms race, trying to find a better adaption to get their resource and protect than the other, like a Tom & Jerry cartoon. It often happens like this: A hunting party of lions brings down their lunch. A pack of hyenas is attracted by the overpowering scent of fresh meat. And now.... Notice, the confrontation ended in a surrender. Why was this? Notice that the two sides were not making much attempt to attack each other. Why? Because both sides know how lethal the enemy is. The predators have been fighting each other for a very long time, ever since they met, for they shared a common goal: to kill their prey and have food. They hunt the same prey, so they will conflict, that is certain. Because of all the conflicts, both species have evolved habits to try to foil the other, for instance the hyenas' tendency to hunt in larger groups and call for back up. This is an excellent example of competition in the natural world and how it affects the competitors. "We lose, but they do not win?"
- Heavy Weapons Guy As we discussed at the beginning, the Pokemon franchise's version of "evolution" is highly innacurrate. (Not that it was ever meant to be accurate...) The creatures are shown to suddenly change into a different creature upon reaching a high enough levels. This could probably be described as metamorphosis, when an organism undergoes a change into another stage of it's life. Evolution happens within a population, not the individual. I could go on and on about the biological innacuracies of the Pokemon franchise, but instead I can show you some examples of what I'm talking about with this whole population thing. Let's start with this:
What's up with this alligator? Anyone? Anyone? That's right it's albino! (If you didn't get that then shame on you.) Albinism is when an animal lacks most pigment in it's fur, hair, eyes, and skin. This is due to a shortage of the hormone melanin. Albinism can be accomponied blindeness and deafness. Any vertabrate can be born with albinism You're probably wondering what this has do to do with anything. Well, these animals look different. Does that mean they have evolved? Abso-freaking-lutely not! Just because an organism has a weird trait that is not normally in the creature's gene pool, the collective genetic intructions in a population of organisms, does not mean it has evolved. To evolve, the entire population's gene pool must gain a new trait. Now, if 75% of the world's mice were albino, then yes, the mouse population now most likely has the gene for albinism in their gene pool. One individual mouse that is albino, however, is simply a recessive mutation. In other words, a species cannot evolve unless the mutant trait is present in the genes of all of the organisms. So, what have we learned? ? 1. Evolution is the cause of all of earth's biodiversity. Without it we would not exist. 2. Evolution uses old adaptions to make new ones. 3. Variation, finite resources, and competition can influence evolution. 4. Evolution works on the population, not the individual. Dang. I wanted wings. Oh, and by the way, evolution certainly isn't done with us yet. Humans can try to avoid it, but life is still evolving, and we will eventually have to evolve too. Nature will make sure we do. Thank you for viewing my presentation and remember... Is everywhere. You can't hide from it. Music: The Greatest Show on Earth By John D. Boswell (Instrumental) CREDITS