[Music] in this video we'll be looking at evolution and this is found in paper two and it consists of around 66 marks so it is quite a big chapter so in this video we'll be specifically looking at the definition for biological evolution we'll look at the difference between a hypothesis and a theory then we'll look at the theory of evolution we'll look at the evidence for evolution that we have and then we'll look at what leads to variation so biological evolution refers to the changes that life forms have undergone over long periods of time and then these changes are genetic changes that are inherited in populations of organisms now this can lead to the formation of new species not just for interest sake it can be microevolution so it's changes in the genotype and then it can be macro evolution where new life forms are formed or even new species looking at the difference between a theory and a hypothesis so theory is a well substantiated explanation that has been proven over multiple times by experiments or tests that have been conducted an hypothesis or sorry a hypothesis is an informed assumption that provides a solution and there's also limited evidence at the starting point so there needs to be further investigation that takes place so basically it starts out with a hypothesis and then once there have been multiple experiments that have been taken that have taken place and it has been tested and verified over time then it goes to the next step which is a theory so that brings us to the theory of evolution so it is regarded as a scientific theory since various hypotheses are relating to evolution have been tested and verified over time thus bringing us to the next step which is a theory what evidence for evolution do we have we've got quite a bit so the fossil record and biogeography you have done in great things so we'll just look at these again then we're going to look at modification by descent specifically homologous structures and then we're going to look at genetics so what is the fossil record it is all known fossils across the world but it is not complete as it does not exactly show all the organisms that were alive at the time because not all of the organisms became fossils and if we forgot what a fossil is it is the remains footprints or imprints of an organism that have been preserved in substrate and fossils can actually tell us quite a bit of the environment and the climate that these organisms lived in as an example on the right hand side this is the fossil of a coral now coral you find in oceans and this specific fossil was actually found in kansas which is a state in the united states and as you can see this is a land locked area so there's no water close to kansas or oceans close to it so what on earth is a fossil of coral doing in kansas so that tells us that at some point in time the united states was actually covered by water and was either part of a big ocean at some point do all organisms become fossils no so not all organisms become fossils specifically ones with soft bodies such as a jellyfish it is extremely rare for soft body soft bodied organisms to become fossils as this decomposes quite rapidly after they die another example is this carcass of the of a cow this will not become fossilized because it will most likely decompose before anything can happen for it to become a fossil now there are specific processes that have to occur high pressure low oxygen and rapid burial now the high pressure is not a stressful situation it's the pressure that is exerted on the organism that has died so for example if we look at this dinosaur that has died quite close to the water here eventually all of the soft tissue will decompose and you're only left with the bone sometimes these organisms are buried before the soft tissue even decomposes so in this case the soft tissue is decomposed but then something happens for example there's a flood or the water level rises for some reason and the bones get buried under sediment and mud and silt and what have you so oxygen is removed from the equation here is there's quite a rapid a rapid burial specifically with floods and then sediments compact on this over time which exerts a high pressure on the bones now what will happen is blood and the bone marrow and all of those things will disappear over time and they are actually replaced by minerals that come in through the water and help harden the bones and stuff like the calcium that also hardens keeps the bones hard just become reinforced so over time maybe the soil erosion that takes place and that bone or those bones then get exposed or the fossil and then somebody gets to make a discovery now it's not just in in rock and sand that we find fossils you also find fossils such as this one which is an amber fossil and this is actually sap from a tree that is hardened around an insect and they can actually take and partially sequence the dna of these insects which led to the premise for the jurassic park films all of the jurassic park forms were built around this little kitty that this scientist had with a mosquito in it and then they created a whole bunch of dinosaurs and you know the rest of the movies tarpets also very good at preserving organisms so this specific topic is in los angeles and they've found quite a few fossils in there as well now we've got very clever people that are able to age fossils and based off of that we've got a timeline that has been built with the different peras periods eras and eons based on the ages of those fossils and then we can also place the organisms in these different periods depending on how old their fossils are so all the fossils are deeper uh very deep in in substrate or sediment where younger fossils are more shallow and looking at this sedimentary rock you can actually see the layers here so it's almost like dating a tree using the rings we can look at the different layers and determine the aegia so what they are saying is that all the fossils are buried down deeper whereas younger ones are at the top and i'm sure this does not need further explanation as to how that happens plants also get fossilized although plants with with harder leaves do tend to preserve better than softer leaves as they decompose quicker but this is what fossil fuels are made of it's plant material that has been fossilized now this fossil on the left-hand side is quite unique as not all fossils preserve as well as this and sometimes the bones are quite scattered or broken so this is a very nice fossil and then you also get trace fossils such as footprints which can tell us a bit more about the the organism and the life and lead and then you get transitional fossils like archaeopteryx which is the transition between birds and reptiles which is quite interesting as well that you also did in grade 10 so you should remember what archaeopteryx is all about then biogeography so biogeography comes to the conclusion that there are distinct geographical regions in which extinct and existing organisms are found closely related organisms are most likely to share common ancestor since they are found in the same area so new species can be formed when organisms are separated by a geographical barrier so oceans mountains and deserts if you don't have an airplane or a boat or something to get across these you are not going to be able uh to get to your friends so as an example uh this population of snails became separated by geographical barrier and they were distinct uh selection pressures that occurred on either side of this and this actually led to new species on either side so when these snails meet again or if they ever do meet again they won't be able to interbreed because there has been so many changes that have occurred that they've become new species but we'll look at that a bit later on so areas that share similar characteristics such as climates and habitats can have completely different kinds of animals for example in africa south america and australia where we share similar climates we've got very different animals that occur and then a very good example of biogeography is large birds such as the ostrich the emu the moa and the rear so you can see that all of these birds look quite similar and it is believed that at some point they shared a common ancestor but then they got separated and new species formed next is modification by descent so different body parts have been adapted to the environment for sp for optimal function in their specific environments so in this we're looking at modification in vertebrates specifically so here we're looking at the forums of different animals that have different functions and look slightly different but they have the same basic body plan and we call these homologous structures so homologous literally means same location so this is an ever this is evidence for a common ancestor now the parts that have the same basic body plan but they have different function functions as for example in humans of forearms we have a bone called the humerus then the radius and the ulna carpals metacarpals and phalanges and you'll see these similar structures in cats you'll see them in whales and then in bats as well and the bones that are similar will be the same color so you can see where they all come along with now looking at the phalanges so our fingers in cats they've been modified to make the poor in whales they have become quite long for the flippers so they're able to swim and in bats they are quite long as well in the wing structure itself that enables them to fly now we're going to look at modification in a species so species that changed over time to form the species we have today now these changes occurred so that they could adapt to the environment now looking at elephants today we have the asian and the african elephant and they share a common ancestor which changed over time to adapt to the environment i mean the step mammoth and the woolly mammoth these both lived in very cold periods so they've got these massive thick furs but that obviously has changed into the asian and the african elephant that we have today based off the changes that occurred in the environment the modern horse came from this little guy over here so obviously changes occurred for them to adapt to the environment and then we have the modern horse of today so genetics is also a evidence for evolution so organisms that are closely related will have similar dna the genotype and the phenotype are transferred between generations and gene pools can change and form new species so basically when these new species form we can look at the dna the more dna that they share the closer related they are next we'll look at everything that causes variation but before that let's quickly look at the definition for biological species and then a population so biological species is a group of organisms that have similar characteristics and can interbreed to produce very important fertile offspring now a donkey and a horse can also cross breed because they share similar characteristics and their chromosome amount is not too far apart but they will not produce a fertile offspring they will produce infertile offspring which is a new now population so a population is a group of organisms of the same species that lives together in a defined area at a given time and they can interbreed so for example you've got a kudu population in the kruger national park they are all the same species they live in a defined area which is the kruger national park and at the same time and they are able to interbreed with each other so let's look at the things that cause variation crossing over and random arrangement of chromosomes we looked at when we did the chapter on meiosis so you should be familiar with crossing over if you forgot what that is just go back and look at those videos so crossing over takes place in prophase one of meiosis and it is an exchange of genetic material between the maternal and the putin or chromosomes uh that then lead to uh variation so as you can see they are swapping genetic merit material so now you have these very unique chromosomes random arrangement of chromosomes so during metaphase the chromosomes are randomly arranged which allows for new combinations to form so out of these you have quite a few combinations then that can occur which leads to variation random fertilization is also a form of variation so between a different egg and sperm cells that may fuse so in humans we know one egg cell is released but then you've got millions and millions of sperm cells that could potentially fertilize that egg but only one is the winner so as an example for variation already it can be a girl or a boy based on the chromosomes that the sperm cell carries and then you've got different things based on genetics we did that already so you can just go have a look at that again but that can also lead to variation random mating so between organisms within a species this beetle could potentially have three different mates each with unique characteristics of their own and then lastly mutation also leads to variation because of the changes in the structure of a gene or a chromosome that occur then there's also two types of variation continuous and discontinuous variation so with continuous variation there are no distinct categories and there's no limit on the value so in this case height weight heart rate finger length and then if we look at plants the leaf length so in your class there'll be a wide variety of different heights ranging from let's say 1.5 to the tallest guy in the class that made might be 1.8 meters tall weight will be different weights in the class and then this is generally shown on a line graph because there are no distinct categories this continuous variation there are distinct categories there's no in between categories an example of this is tongue rolling you can either run roll your tongue or you cannot your fingerprints fingerprints is a form of discontinuous variation because this never changes you're born with your fingerprints and they will stay like that for the rest of your life as will your eye color and your blood groups so whether your blood group a a b b or o your blood group never changes and they are distinct categories so we can place them in graphs such as a bar graph or a histogram and that is the end of the first part of evolution [Music] you