Human Evolution Skeletal Structure

Hi everybody and welcome back to Miss Angler's biology class. I am Miss Angler. In today's video we are going to be looking at an introduction to human evolution where we're going to focus on the similarities and differences that we see between us and other primates. I'm also going to walk you through how you can use this information to best explain yourself in an exam or a test because often in this particular topic we learn a lot of facts but we're not so sure how they're going to ask the question and what to expect. Now if you are new here don't forget to give this video a thumbs up and make sure you are subscribed with your notifications turned on because I post new content every Tuesday and Thursday and if you are in matric and you're thinking about improving your mark and getting a distinction at the end of the year you might want to join my membership. In the membership you have live lessons with me, you get access to my study guide for free, member only videos and so much more. Now before we get into this it's really important that we know how to navigate the family tree and also to understand what we're actually talking about when we use the word primate or hominid and where do we fit? Are we a monkey? Are we an ape? And so I'm going to quickly break that down for you and one of the skills you need for the exams is being able to navigate through a phylogenetic tree or a cladogram like the one that we see in front of us here. Now essentially what you see here as the heading suggests is a primate tree of life. In other words you can see us sitting at the end over here with all of our cousins. Now it's important to also note that this has been constructed, this particular one has been constructed in such a way that it is showing how distant they are from us. In other words the individuals that are closest to our left over here are more similar to us than perhaps the lemur over here which is the furthest away from us. Now it's important to know that humans are not monkeys, we are not gorillas, we are not gibbons or any of these other monkeys that you can see here on the slide. Instead we are what we call apes and apes are this final category at the very end over here and we're grouped together with orangutans, gorillas, chimpanzees, bonobo chimps and there's us humans at the very end. So that's the particular category that we're going to talk about. Now something I want to highlight to you is how to actually navigate your way through diagrams like this in exams and in tests. So what you're actually looking for here is how related each individual is and we can actually calculate that by how many common ancestors they share. So this is a cladogram, it's a version of a phylogenetic tree. There are some slight differences, this one doesn't have any time on it. Phylogenetic trees generally have time scales on them but what you do have which is is you have these points where there seems to be like a break off point. In other words, an organism breaks off to the left here while the main line continues forwards or straight or up. And those little breaks, every time there is a break, this little intersection creates something called a common ancestor. Now common ancestors are really important because they show us how related we are to one another and the more ancestors you share the more closely related you are. And to give this a perfect example of something that they may ask you in an exam is they may say are humans more closely related to orangutans or to gorillas, let's say for example. Now the only way to actually physically say this correctly is not to say well because of the diagram the gorilla is closer therefore you know they must be closer to us in relation. It's not about closeness in the diagram. What it is about is how many of these little intersections do we share with that organism. So if we count how many humans share with orangutans then what we are looking for is how many we have before they split off. So between humans and orangutans we share 1, 2, 3, 4, 5, 6. So we've got six with orangutans. On gorillas on the other hand we share 1, 2, 3, 4, 5, 6, 7. So the moment they deviate and they diverge that's where we need to stop counting. So because we have seven ancestors shared with gorillas we're technically closer in relation to them than we are to orangutans. Now going into the next important piece of information that you need to be able to work with along with what we just saw now with the cladogram or the phylogenetic tree you may be asked to interpret. You may also be asked to explain or even provide a table maybe of the similarities that we share with other apes. And I'm just going to run through the top six things that we share with apes and the list is actually quite long. It can actually continue but these are the main six that we share. First of all the most important thing that we share with other apes is opposable thumbs and the picture alongside really highlights two of the key things that we can do with our thumbs. We have a great grip with our thumb which means we can use our thumbs to hold on to things but we also have precision. Now this precision grip makes it really easy to use tools which again is something that separates us from other primates and for that matter from other apes as well. Now the second thing that we have in common is we have no external tails. So all chimpanzees, all gorillas, if you think about it orangutans, they don't have tails and neither do we. But if you compare us to monkeys, monkeys have tails. Things like lemurs, vervet monkeys, they all have tails. So we don't have tails therefore that is something we have in common. We have bare fingertips which means we don't have any claws. We have binocular vision which means our eyes are placed in the front of our heads and we don't have any blind spot in the centre of our vision because our eyes are close enough together. In other words they're not too far on either side of our heads. The fifth thing that we have is colour vision and this might surprise you but not all animals have colour vision or the depth of colour vision that we have and we can see pretty much all of the spectrums of coloured light or visible light. And the last thing is that the males are larger than females. We call this and some textbooks call this sexually dimorphic as well. It basically means that there is a male and a female sex and the males are often larger. Now in terms of how they can ask this, they don't really ask more than maybe three similarities but what is important that you must pay attention to is often they're going to ask you these similarities that we might have and then perhaps why they might be useful. So for example if we think about why is it useful to have opposable thumbs. Well it's useful because you can grip things, you can hold things, you can make tools. The next thing they may ask you is why is it useful to have binocular vision. Well your eyes are in the front of your head, you can see danger, you can see predators or you're able to hunt better. And likewise with colour vision it improves our ability to differentiate between things that are maybe poisonous or be able to see warning signs and warning colours in animals. So you may be asked to give a similarity and then substantiate your answer like give a reason as to why it is a useful thing to have. Next we need to go into the skeletal differences and first of all we're going to focus on the skull. There is a lot of differences in the skulls that we need to point out and that you need to know. The good news is that in terms of how many you should know if you need to like write them down as a list, you probably really only need to know about three differences because often they ask you to tabulate the differences. The reason why perhaps you should also spend some time familiarising yourself with any of these differences is often what they ask you is they'll say something like according to the picture in the text or in the exam what is the difference between skull A and skull B and then you have to give the differences that you can visually see. So you need to have at least three differences that you can remember off by heart when looking at a picture or if asked for a list. Now we're going to start off with the most common and the most well-known difference between us and primates and that is going to be the location of the foramen magnum which we can see in the picture alongside here. Now the foramen magnum is the largest nerve hole or opening in the body and it is where the spinal cord leaves the cranium, the skull, and goes down the full length of your vertebral column. Now what you will notice is that the human foramen magnum is positioned more forward and that's really important to use those words. You shouldn't use more central or in the centre that's a no no no no. So we are not going to use those words we are going to use it's more forward and for apes we're going to say it's more backward. Then in terms of the other differences we're going to take a look at this other diagram on the left hand side here and there are quite a number of differences and I'm going to start off with some of the easier ones. The first is going to have to be the jaw and you will notice a difference between the two in size and what we call this very pronounced jaw is a prognathous jaw. Now again there is some terminology that you must use and then also you must avoid. When you talk about the size of the jaw or the fact that it's like big and bulky like this first photo we say that's a prognathous jaw. When you talk about the human jaw you need to say that it is non-prognathous. You cannot use the words less prognathous or decreasing prognathism you need to say prognathous or non-prognathous. The next skeletal difference I want to highlight to you is a feature on the front of our face which is this over here the brow bone. Now in apes you will notice that the brow bone is really really really really pronounced it's also known as the brow ridge but in humans you'll know it's greatly reduced you see it's barely visible on this picture. The next thing that's really different in our skeletons is going to be the size of our cranium. Now the cranium in both of these pictures is vastly different in sizes. Humans have a large cranium whereas our cousins have a much smaller cranium and that's because the size of our brain is getting much bigger. The next difference I want to highlight to you is going to have to be the canine teeth so these teeth over here and what's really interesting is the canines are really large in primates in other primates but if you'll notice in humans they're quite reduced and quite small and almost not noticeable. Another important feature in terms of skull differences is going to have to be a little area on the back of the skull and I'm just going to move some of these labels so you can see it better and you'll notice it almost looks like the skull has a ridge to it and I just want to highlight it it's this area over here you'll notice that we're sort of missing it over on our own and that structure is known as the sagittal crest. Now the sagittal crest did have a purpose in our ancestors and also in our cousins and I'm going to touch on that when I go through hominid evolution and phases of hominid evolution in the next video but we're actually missing it and the main reason why we're missing this little extra like piece of bone this little it almost looks like a fin is because essentially our chewing muscles in our cheeks have gotten smaller because we cook our food and so we don't need this extra piece to our skull to attach the muscle to. Now just briefly going back to the first point I made about the foramen magnum. The foramen magnum is probably the most important indicator and skull difference for when it comes to an organism being able to walk on two legs which is a really important difference because humans walk on two legs all the time whereas chimpanzees and gorillas orangutans other primates they don't. They might spend some time on two legs but they don't spend the majority of their time. Now the word associated with the foramen magnum and being able to walk on two legs is called bipedalism and this is one of the most important developments in our evolution that we must note and be aware of when we do this topic especially with this foramen magnum and in the next two skeletal differences and what they look like and how they assist bipedalism. Now as I mentioned the foramen magnum is the most important thing for bipedalism but we also need to look at the structural differences between the pelvis and the feet of other primates versus humans because it also tells us a story about whether or not these organisms could walk on two legs or not. I'm going to start off with the feet and if you have a look here we have a gorilla and a human and one of the most classic classic things that you should look for in these diagrams is what we call a divergent toe. Now you will notice that the gorilla has a very large divergent toe. There's a big space in between the big toe and the next toe. In humans you will notice it isn't there. There is no space so our toes are not divergent. You could also technically say they're convergent. They come together. Another important difference in our feet if you compare gorillas to humans and again this all supports bipedalism because remember that's the goal. These skeletal differences must support the idea of bipedalism is the size of the heel bone. Now the heel bone in humans is much larger and that's because we spend so much time on two feet. We need to put all our body weight into this bone and so the bone needs to be bigger and stronger. In gorillas it's smaller because they spend very little time on their two feet. Then we move on to the pelvis. Now again the pelvis plays a really important role in bipedalism and you need to be able to tell the difference between any kind of diagram that you're given. You need to be able to identify which one is the chimpanzee or which one is the ape and which one is the human. Now when we look at these two there are some key things I want you to notice. First of all I want you to notice that the chimpanzee pelvis is reasonably longer if you notice compared to our own and you'll also notice that it is very narrow. Humans on the other hand we have a shorter pelvis but we have a much wider or broader pelvis. So when you're explaining this in the exam or a test I suggest that you go for a description like this. You want to go for a long narrow pelvis for describing chimpanzees or apes. When you're describing humans you want to say short and you want to say wide. Now again they're going to ask you why. The questions always turn back to why is it long and narrow? Why is it short and wide? Well it's short and wide in humans because we are bipedal and we need to carry our body weight upright and so the shape of our pelvis supports that better and it allows us to have a center of gravity right in the middle of our body. Whereas chimpanzees have long narrow pelvises because they spend more time on all fours their body weight leans more in their chest so on the top of their body they're heavier on their top and so their bones need to be longer because they spend more time parallel to the ground and so that's why you need to be able to say the structure and then give a reason for the structure. Now as always I like to finish off my lessons with a terminology recap. Please use these words for flashcards, mind mapping your ideas out. It makes it really quick and easy to do revision. Now first of all we spoke about primates. Remember primates are all of our cousins including monkeys and gorillas and so it's a very wide family tree. However if you start to focus in specifically on us and our most close relatives we would use the word hominid and I'm going to go into more detail in our own specific hominid evolution in the next video and how we went from Australopithecus to Homo sapien. We then looked at some key features and some of them are easier to remember than others but one of the most important similarities is the opposable thumbs that we share with primates and the binocular vision that we share with them. Then we went into the differences. Now the differences again are really important to know specifically one of the most important is the foramen magnum which is the location of where the spinal cord goes into the brain or vice versa where the spinal cord leaves the brain and that location is linked to bipedalism. Now bipedalism is the most important evolutionary change that's happened in humans and so whenever you are talking about well why is the pelvis the shape why is the foot the shape it all slowly but surely comes back to being able to walk on two feet our hands are free we can make tools and there's so much that you could like speak about on that that I'm going to touch on in the next video. We also spoke about the prognathus jaw and humans don't have a prognathus jaw we've got quite a a small jaw and so when we say what it is we say non-prognathus whereas other primates have a prognathus jaw. We then spoke about the differences in the cranium size so we have a very large cranium with no sagittal crest whereas primates have a small cranium and many of them have a sagittal crest on the top. The last important difference is the canines. The canines are really large in other primates whereas they're reduced in humans and that comes down to the whole thing about cooking our food and eating cooked food and no longer raw. You see you need bigger canines because when you eat raw food you have to tear it and it takes more effort whereas humans cook our food so there's less effort involved and also we don't use our teeth anymore for territory or for fighting or anymore so we don't need very large teeth. Now if you like this video don't forget to give it a thumbs up and make sure you are subscribed. I post every Tuesday and Thursday so also make sure notifications are turned on and I will see you all again soon. Bye!