[Music] in this video we'll be looking at human evolution and specifically you'll have to interpret a phylogenetic tree to show the place of the family hermena day and then we'll also look at the characteristics that humans share with african apes and then the anatomical differences between african apes and humans with specifically referring to these points listed below bipedalism brain size teeth prognathism pellet shape cranial ridges and brow ridges now with these they can give diagrams with each of these that you then have to be able to interpret then we'll look at the lines of evidence that support the idea of a common ancestor for living hominids this including humans so we'll look at fossil evidence we'll look at the emphasis assist on evolutionary trends specifically with ardopithecus australopithecus and then homo and then we'll look at genetic evidence which includes mitochondrial dna and then cultural evidence which is tool making now the interpretation of a phylogenetic tree we'll get to that in another video in more detail but basically just to understand the taxonomic rank the order in which it goes you have kingdom phylum class order family genus and then species so us as humans would be homo sapiens and then just to write it correctly remember the genus has to be written with a capital letter and then species with a lowercase letter and if you don't have a computer to type it within italics you underline it with your ruler now a mnemonic to remember kingdom phylum order class order family genus and species is katy perry comes over for grape soda just if you need to ever recall that order now looking at the scientific classification of hominids so we all fall under the class mammalia the order primate and then hermenedae is then the family and under that you will have humans which falls under hominini and then you'll have gorillas and orangutans in their own sub-family so that's just the basics of it so just to understand and clarify what hominids are hominids are great apes and humans and then those are further divided into great apes and then hominins specifically which is then ardopithecus australopithecus and homogeneous and or genera and we'll look at those in more detail in another video now what characteristics do humans share with african apes so for this you can just plainly look at your hand during an exam and recall the information just by looking at it so firstly we have an opposable thumb for a power grip in apes and in humans that has become more precise and it has formed a precision grip in humans so on the right hand side here this is a power grip to grasp onto objects and then the precision grip which you'll find in humans is more precise allowing us to have fine motor movements holding pens working with tools and you won't find that in the apes now we both have two hands each with five fingers um and two feet with five toes each then we have long arms that rotate freely at the shoulder joints that allow movements in all directions you won't find that in a dog for example then we have naked fingertips ending in flat nails we have a reduced snout with a weakened sense of smell so that means we have a reduced olfactory center then we also have stereoscopic vision with forward-facing eyes so that gives us 3d vision so it allows a better depth of field then we have eyes that have cone cells cones for color television we also have red cells but more cone cells that allow us to have color vision then the brain centers that process the information from hands and eyes are enlarged for very good hand eye coordination neither humans nor apes have a tail then sexual dimorphism where males and females are clearly distinguished so sexual dimorphism means that when you see a male or a female you can clearly distinguish that it is a male or a female and then we have molars and premolars with rounded cusps moving on to the anatomical differences between humans and apes we are going to start with bipedalism first so bipedalism by means to and pedal means feet so we have two feet and this has allowed us to walk upright and then apes are quadrupedal so chimps and gorillas specifically are knuckle walkers so that means if you look at this diagram at the bottom they have four four limbs on which they walk specifically on their knuckles so that means they are quadripedal four and then pedal for feet now the benefits of bipedalism is quite large so firstly your hands and feet are free to use tools not your hands and feet your hands are free to use tools that you can occupy a wider range of habitats you can see further because your head is in a higher position looking at the diagram here at the top if you were to be on all fours in tall grass you would not be able to see what's happening ahead of you whereas if you are bipedal you can see much further then a large surface area for air to cool down the body and then there's also a smaller surface area from above to prevent overheating by the sun and looking at this diagram it'll explain that so when something is bipedal there's a much larger surface area for wind to touch the body and cool it down and then from the top it's a much smaller surface area for sun exposure whereas if something is walking on all fours there's a much bigger area for sun exposure and a far smaller area for more wind to come and cool the body down now what features make bipedalism possible and you need to know these so the foramen magnum position the shape of the spine and then the pelvis shape we'll look at each of those now so the foramen magnum position is moved forward in the skull with humans and it sits just above the vertebral column now on apes which are quadripedal the foramen magnum is situated at the back of the skull and head in front of the vertebral column so what is the foramen magnum it is this opening here where the the vertebral column comes into the skull so in humans you can see it's quite centrally located whereas in the apes it's more to the back and then as we go through the different hominid hominins you'll see that it it's also located to the back but it's it's moved to the front a bit and this diagram on the right just shows you at what angle it comes into the skull so in humans it's quite centrally located so you need to be able to describe that then the shape of the spine so in apes you have a c-shaped spine and then in humans you have this s-shaped spine and what this does it helps with shock absorption and flexibility in that upright position then pelvis shape this one has popped up in quite a few previous exams so they'll give you a diagram like this and they'll ask you to explain what you see or to identify which powers is which so in humans we have a larger shorter and wider pelvis that will support more weight so if you look at this one you can see it's quite wide and it's not as tall so it's quite short whereas in the apes they've got a very long and a very narrow pelvis as compared to that of a human and then in between you'll have australopithecus or ardipithicus with an intermediate pelvis between african apes or not african apes but apes in general and then humans uh just before we go on just if you look at the femur the point where the the joint goes into the hip socket there you'll see that this area is quite elongated as compared to that of the apes and it's just uh for muscle attachment in that area that will help with bipedalism and then in humans the femur is also much longer than that of africa of the of the apes or the intermediate form of for example australopithecus or ardopithecus moving on to brain size so over time the cranial volume increased allowing for the brain size to increase as well so just as an example an average human brain is around 1.3 to 1.4 kilograms and then a newborn baby's brain is 350 to 400 grams as compared to a chimp which is 384 to 395 grams so you can see that a newborn baby's brain is almost the same size as the chimps so they've got much smaller brains as compared to humans and if we look at this you can see how the brain capacity increased as we went up through the timeline so the further back we go the smaller the brain capacity will be now why is brain size that important so with brain size came the use of fire the development of language and then also the development of tool use and hand eye coordination and these are all linked because of how for example tool use had to be passed on and the only way that tool use could be passed on and how to make it was with verbal communication you would get some through with like communication with hand signals and so on but the best communication obviously happens with language then the dentition and the pallet shape usually go hand in hand as they will give the same upper jaw diagrams for you to analyze so with dentition the size of the teeth became smaller over time so if we look at the teeth size you'll see that there's major canine or massive canines in the apes and then in australopithecus it became smaller and then in humans you have very small canines but what we are looking at here is specifically the gap between the incisors and then the canines so this area that i'm coloring in red now now in chimps or apes it's very pronounced whereas if we go on to australopithecus it's much smaller and then in humans it's completely absent so apes have a large gap between the canines and incisors and in humans the gap between the canines and incisors became absent and then also the enamel of the teeth are very thick as well now one of the reasons that they say our teeth became smaller or our jaws became smaller is with the development of fire because it was making the digestive diet the digestion process of food much easier because as you know digestion starts in the mouth already so it was much easier to process meats and so forth so we no longer needed that massive jaw and it became much smaller then the pallet shape so in apes there's a very narrow pallet shape and in australopithecus you've got a u-shaped pallet that's a very ugly you and then in humans it's wide and curved so that's how you would explain that then prognathism so apes have large protruding jaws they protrude beyond the upper part of the face causing a slope so as you can see this jaw is massive and it comes out below the face and it causes this slope that you see which is then the prognathism then as time passed the teeth and the jaws became smaller and less protruding so as we go down you'll see australopithecus here has a much smaller draw and the slope is also less pronounced and then when we finally get to humans we have a protruding trend but we have smaller jaws and teeth and that causes a vertical slope that you see there so a more vertical forehead then the cranial and brow ridges so because of the shape of the jaws that apes have they have a well-developed cranial and brow ridge for chewing muscle attachment so the brow ridges are these ones that sit above the eye sockets and then the cranial ridge sits here at the back and what this does is it um acts as a as an attachment point for muscle specifically the the chewing muscle so from the jaws to help move these massive jaws up and down when they're chewing so you've got these protruding eyebrow ridges and then the cranial ridges now if we look at hominins you will see that that was reduced over time and then specifically in humans it has almost completely disappeared as you can see that's not as pronounced as with the apes and then we also don't have a cranial ridge present whereas in apes you can't really see it on this diagram they'll have that for the muscle attachment to the jawline then i just put this table on the left here in just as a quick summary so you can pause the video if you want to spend some time looking at this or if you have the answer series part 2 for grade 12 life sciences on page 2.23 it just gives a nice summary of the differences between african apes and humans now we're going to move on to the evidence that supports common ancestor in hominids so we're going to be looking at fossil evidence we're going to be looking at the evolutionary trends provided by the anatomical features of the fossils and then genetic evidence and cultural evidence now evidence from fossils of different ages show that the anatomical characteristics of organisms changed gradually over time and the features that we looked at are bipedalism brain size teeth pragmatism pellet shape cranial ridges and brow ridges so you can just go look at that again that is what we look at for the fossil evidence and the evolutionary trends and then also most hominin fossils are only of the skull and teeth and sometimes they are in very small bits and pieces so it takes a lot of anatomical knowledge for these people to actually compile same i'm saying compile or build a skull just based off of the little material that they have actually found so it's quite amazing how they can do that now genetic evidence so the genetic evidence we use here is chromosomal and mitochondrial dna and chromosomal dna as you guys know it's found in the nucleus you get it from both parents and when we compare the dna of hominids it will determine how closely related they are obviously the more similarities they are the closer related they are and then this genetic evidence will also then support darwin's theory that humans and apes share a common ancestor and then moving on to mitochondrial dna also known as mtdna now this is found in the mitochondria and with specifically with this it is only found or they only trace it with females because when um the sperm cell moves towards the egg cell the sperm cells mitochondria stays behind as only the head goes into this the egg cell to fertilize it so the only mitochondrial dna that is passed on is from the female now there is some recent studies that have found that in certain cases men's uh mitochondrial dna is also passed on but that is very rare uh so generally speaking it is only the female mitochondrial dna that is passed on so whether you're male or female you have the exact same mitochondrial dna as your mother her mother before her her mother before her and so it goes back all the way and that is actually how they were able to find um a recent or not a reason but a common female ancestor known as mitochondrial eve and this is her down here so this is what they think mitochondrial eve looked like this is not necessary that she was the first female that ever lived it's just it's the first one that they could trace back um to a common ancestor they can do the same with men as well using the y chromosome so y chromosomal atom is this chap over here he did not live the same time as mitochondrial eve just to put that and clear that out but this is what they think he looked like so when there are many similarities between the mitochondrial dna so that means that they are separated they separated late and less mutations occurred obviously the closer related they are but if there are many differences it means they separated very early which means more mutations occurred which means that they aren't as closely related and then lastly we're looking at cultural evidence specifically tools here so using of tools fire making burying the dead art hunting are all evidence for a common ancestor for living hominids now speech and language were necessary to communicate when hunting or passing down knowledge such as tool making so with tool making you got an increased intelligence and dexterity which is the part of the brain that controls this is quite large now apes use tools like stones and sticks but very important is they do not make them yes they use them but they do not make them most tools are made of stone but then bone ivory and wood are also used now stone lasted longer with the test of time and those are generally the ones that you would get in in archaeological sites when they dig them up and then the first one to use stone tools is homo habilis also known as the handyman now what are the benefits of tool use so firstly you are able to make use of other food sources they could kill larger prey and then the preparation and cooking of food was made much easier so you get different types of tools obviously like you would get in your dad's toolbox now you would get a hammer you would get pliers and all those kinds of things you would also get different tools that were used for different things back then and generally how they made them was firstly using bigger rocks to chop away at it creating these sharper edges and then they'd refine them by scraping or grinding them or using other tools to to make them a bit sharper so that's the end of this first part of human [Music] evolution you