hi everybody and welcome back to miss angus biology class i am miss angler and in today's video we are going to be looking at lamarchism we're going to look at his theory how we use his principles to explain evolution and to go through the basics and make sure that you'd be able to apply lamarcusm to any kind of exam question that you may see now if you are new here don't forget to give this video a thumbs up subscribe and make sure your notifications are turned on because i post new content every tuesday and thursday if you are in matrick and finals are coming up very soon and you need that little bit of extra help you should think about joining my membership there are so many perks including members only videos live lessons with me and of course a free copy of my study guide is included for those of you who join the rescue me option so before we start off looking at lamarck's principles we just need to put his theory into context so that you know exactly how he came to these conclusions and why is it that we don't actually consider lamarcism a reasonable way to explain evolution today a couple of things we need to keep in mind is lamarck would have formulated his theory long before genetics which means that in the terms of explaining how things are inherited genetics hadn't been discovered yet so lamarck would have been before mandel remember mandel we learned earlier in the year about genetics he explained how we inherited things lamarck had no information on that just yet so we couldn't necessarily base our explanation of evolution on that genetics just yet another thing as well that wasn't very well identified just yet was dna now obviously dna is a component of genetics but likewise there wasn't very much clear data at that point about what dna was and what it's made out of and how it moves from individual to individual all we knew at this point during lamarck is that somehow offspring looks similar to their parents and obviously some kind of information has been passed from one organism to the next but we didn't know what those things were just yet and so lamarck looked for a way to describe and explain how it would be possible that organisms came to look and behave the way they do today why do they have the structures that they have and how is it possible to then give that onto their offspring in order to truly understand lamarcusm we need to look at his hypothesis which was the inheritance of acquired characteristics now this particular hypothesis has two main fundamental principles that govern it and support this theory and he used these to explain how it works you'll notice one of them when i show it to you is a repeat of the theory's name i don't want you to be too worried about that i'm going to explain why that is the case soon what i want to do first though is just quickly break down the name of his theory so that we are on the same page and we understand where he's coming from with this so when we speak about inheritance let's not forget that this is the way in which organisms uh pass on characteristics from parents to offspring no lamarck didn't know about genes and genetics just yet but he knew that there was like something that was being passed on then we look at the word acquired now acquired means you gained this trait or characteristic throughout the course of your life and you are going to then pass it on and you'll see now why that doesn't quite work when it comes to genetics that you can't just inherit things that you've acquired through the course of your life now when we explain this particular hypothesis we use the first principle of use and disuse which is a fairly simple and straightforward idea and it's broken down into a couple of parts but essentially what it is is if we have a look here it is the organism that is responding to the environment which in other words means the organism has decided itself that it wants to respond to whatever has changed it's gotten hotter it's gotten colder their food is underwater maybe maybe they need to fly now and they are responding to it and when they responded to these changes in the environment they're doing it actively which means that they're actively changing their body to survive now we know that this is not the case just because you want to be able to fly it doesn't mean you can fly doesn't mean you can grow wings or feathers and so for this theory to work an organism would need to actively be able to change their physiology or change their anatomy and as we know this is not the case you cannot will something to happen you don't want to be you can't will to be taller and then you're going to grow taller um and to sort of explain this even further he used the idea of using something more or less and he suggested that if you were to use a structure more it would become bigger or stronger if you were to use a structure less it becomes smaller and weaker until eventually it actually disappears and for some instances this is quite confusing because to some people this makes sense it makes common sense if i use my legs more they will become more muscular yes that is the case they will become more muscular but you can't necessarily grow longer legs you can't grow another leg so it's important to know that when we speak about these users and how you change your structures you are just changing them also within yourself which brings me to the second main component of this theory which as i mentioned to you at the beginning of this that the inheritance of acquired characteristics comes up twice and the reason for that is we are speaking about the phenotypic changes or the physical changes that we see in organisms now as we've already learned in our previous topic the physical changes that happen to you in genetics it cannot affect your your your genotype so for example if you dye your hair pink that is a phenotypic change that phenotypic change cannot be translated to your dna and then passed on to your children in other words you dyed your hair pink that is now part of your dna and it's passed on to your children so they have pink hair that is not the case okay but however to lamarck he theorized and used this as a principle and said well actually the way in which organisms change during the course of their life there's physical phenotypic changes they are acquired by the parent and then during their lifetime they've acquired it and they're going to pass it on to their offspring now as i just mentioned that's just not the case we can't change our physical characteristics and then our dna follows those two things are not linked to one another in that way specifically your genes can make your phenotype and they do but your phenotype cannot influence your genotype so things you physically change to yourself in your course of your lifetime can't affect the way you look or behave now to apply this idea one of the most common examples is the one i have alongside here which is lamarck's giraffes and basically it was a way in which landmark was trying to explain how giraffes got longer necks now originally if we start with the first generation giraffes began with a short nick which is actually true that is an evolutionary thing they did have shortened x and over time their necks actually did get longer as time went along and he would have described it in uh in his own two theories and principles he would have said something along the lines of the food was out of reach for our giraffes so what did they do they actively responded to the environment by stretching their necks making them longer so that they could reach the leaves they then passed on that physical phenotypic change to their offspring and their offspring were born with longer necks and then the cycle repeated the next generation was slightly longer necks did it again they responded to the environment they actively adapted to their new environment making their neck longer that physical change was then passed on to their offspring resulting in the third generation with an even longer neck and so on and so forth so when you are explaining this in an exam you need to use these two principles use and disuse and the inheritance of acquired characteristics those two to explain any kind of example you may meet now what i would like to do now is just a very quick application example so if you ever come across this in an exam you know exactly what to do because they don't always give you the giraffe example they can give you any animal and they'll ask something like using lamarck's theory or how would have lamarck explained um the way in which lizards lost their legs and became snakes so when you're formulating your answer you must mention both of his principles under his theory the first one of course being the law of use and of disuse now in this instance when we're speaking about our lizard we are going to focus more on the disuse side right because remember you're going to say something like lizards used their legs less and because they you use their legs less their legs disappeared and they no longer have any legs right they become weaker over time they didn't need them the second thing that you need to do in your answer remember is to speak about the inheritance of a quiet characteristics and when we speak about that remember we're talking about passing it on to our offspring so what we do in the next part of our answer is we need to speak about how that change which is the no leg or if you don't want to go straight to no leg you could also say smaller legs or weaker legs and you're going to say that that characteristic is then passed on to offspring now it is important of course to mention in your explanation that all of this is occurring because your lizard is responding to the environment and it might be because there's more food there's less food maybe there's a temperature change but essentially um you need to say that this has happened because the lizard is responding to the environment and they are actively and that's another important word we want to put in there we want to say that they are actively changing themselves it means that they know that they're changing themselves and they're doing it on purpose and that's basically it and you can apply to any kind of animal or person or behavior take the principles as i mentioned in the previous section of the video and just apply it to the topic that you're working with and make sure that you speak about that specific example that they're asking about if they want giraffes they'll ask for giraffes so if they want a general explanation just give them a general one you don't have to use any kind of specific structure or animal only work with what they give you now as always i like to do a terminology recap at the end of every session and this particular one's gonna be very quick because we didn't do a lot of terms we rather just did some application and some theories and so remember when we are speaking about lamarcusm we are speaking about the uh theory in which organisms have um actively changed their bodies and have passed that on to their offspring we also then looked at the fact that lamarck speaks about a phenotype change in other words it's a phenotypic thing that's happening remember that doesn't actually work because you can't change your physical characteristics and then change your dna and then we looked at these two principles which was the use and disuse principle use it more becomes stronger use it less becomes weaker and then eventually disappears and then the acquired characteristics those are the ones that are accumulated during the course of the organism's life and then passed on to their offspring now if you like this video don't forget to give it a thumbs up and make sure you are subscribed with the notifications on and i'll see you all again soon bye