 Sexual reproduction which involves creating offsprings from two parents definitely requires more efforts because one needs to find a mate of the opposite sex and then together they reproduce to create offsprings. So clearly it takes more efforts compared to asexual reproduction where only one parent is involved. So the big question I want to try and answer in this question in this video is why did nature evolve this? What's the advantage of sexual reproduction over asexual reproduction? Well let me give you the answer right away because it turns out that in sexual reproduction we get faster variations. You get faster variations. But what does that mean? Well let's use the rest of the video to try and understand this with great detail. So what exactly are these variations? Well we've talked about them in previous videos. In short whenever a cell is ready to divide or reproduce make a copy of itself. The DNA first makes a copy of itself and the DNA copying mechanism is not perfect. So some errors are introduced and as a result the new cell may have some variations compared to the initial cell. And why are they important? They're important because they help species adapt to the ever changing environment of our planet. Now of course if you need more details on what I just said then we have a dedicated video on this called variations. Feel free to go back and check that video out. But anyways since variations are important it makes sense to have these variations faster and that's basically why we have sexual reproduction. But to understand how sexual reproduction helps and makes variations faster let's first go back to something that we already know asexual reproduction. So let's take the example of asexual reproduction. Let's say reproduction by some bacterium. So what I've drawn is just the nucleus of that bacterium. I've not drawn the entire body and this is its DNA. Now when that bacterium is ready to divide it's gonna make a copy of that DNA and that DNA will have some errors. But think about this DNA itself. Even this has accumulated lots and lots of variations because of millions and millions of errors that got accumulated during millions and millions of copying. So if I compare this DNA with some ancient ancestral DNA it also has lots of errors accumulated. And let me show that by drawing some red spots. These are all the millions of errors that got accumulated over millions of years let's say. And now when this one makes a copy of itself it will not make a perfect copy. It'll introduce an additional error. So let's say that additional error gets introduced somewhere over here. I'm gonna represent that with a blue. So this is the new error that got introduced. So this is the new error causing variation in the offspring as well compared to the parent. But here's the thing. If you look at the overall DNA structure of this compared to this one it looks pretty much the same because the error the new error introduced is so tiny it may not even cause any significant variation. In other words this offspring might look identical to the parent. Very good chance. That's the reason why we say offsprings are clones of the parents. Because in most cases the new errors introduced are so insignificantly tiny it won't matter at all. And the same thing is gonna happen when this one reproduces. Again it's going to add up a new error but overall the DNA will pretty much still look the same. So in short variations are very slow in asexual reproduction. Only after lots and lots and lots of copying maybe the errors will accumulate enough to produce some significant variations. Right and therefore we have to wait for a long time to see these variations. That's why variations in asexual reproduction are super slow. So variations are slow. And so the big question now is how do we speed it up? Well immediately one thing we may think of is we might say then why not just introduce more errors while copying the DNA. Let's just make the DNA copying mechanism more imperfect. Right so let's say the copying mechanism was so imperfect that there were many errors introduced while making the copy. When that's all the problem one won't now variations be faster. Answer is no. Why? Well because if you introduce lots of errors in the DNA copying mechanism there's a good chance the DNA won't even work. The cell might just die. Remember DNA is kind of like a recipe for that cell to understand what proteins to get built. And if you introduce too many errors we might have too many errors in the proteins that get built and the cell may not even function properly. It's kind of like when you copy a cooking recipe to you know bake something maybe bake a cake or something. You might change things a little bit here and there randomly not purposely but randomly you might change things a little bit here and there and that still won't cause much changes in the final cake that comes out. But maybe if you change a lot of things in a lot of places and a lot of drastic changes like you know maybe you add two cups of extra sugar or maybe you add 10 liters of extra milk I don't know. Then your cake will be uneatable or it won't even get baked maybe. Right so this is completely out of option. You cannot do this. Errors need to be introduced slowly and since variations are dependent on the errors that means the variations also will be very very slow. So what to do. This is the reason nature came up with a new kind of reproduction all together. Sexual reproduction. And as we will see this technique doesn't solely depend on errors for introducing variations. Errors are definitely required but there is another way in which it introduces variations in its offspring. Let's see how. Over here the cells from two different individuals one male and one female basically opposite sexes they combine to give you an offspring. And now the most important point of the sexual reproduction is to realize that the DNA of these two parents are not identical. Right the variations accumulated in the DNA of one parent will be different than the variations accumulated in the DNA of the other parent. So again I'm going to draw them with red spots. I'm showing them in different places just to show that these set of variations are different than the set of variations over here. And how do I know that? I know that because they don't look the same. Right they have different eye color hair color maybe different texture of the skin height will be different so many differences they will have. So clearly the variations accumulated in one DNA is not the same as accumulated in the other DNA and this is the most important thing. And so now when that's when a new offspring cell is formed basically it gets a copy from both the mother and the father. So here is the copy of the mother here is the copy of the father let's say it gets both these copies. It's a combination of the two DNA. And as a result if you now compare the offspring's DNA with say the father it's not the same because it has variations from the mother so it won't look like the father. Similarly if you compare the DNA of the offspring with the mother it won't look the same because it also has variations from the father and so this will not look like a mother. And so the offspring will neither look like a father not like the mother but it'll be unique because it has its own unique set of variations. And this is why in sexual reproduction offsprings don't look like clones of their parents. You and I resemble our parents of course but we don't look like clones of them like in asexual reproduction. Therefore we can immediately see very quickly variations get accumulated. And again when this person is ready to find a mate and start reproducing more variations get accumulated because of the combination of their DNA. And so immediately you can see in sexual reproduction variations are faster. Now of course you may be having a lot of questions one question around maybe what do we mean by DNA gets combined what is the meaning of combination or do they get attached to each other or does the nucleus of the new offspring will just end up with two sets of DNA. Does the DNA keep on increasing? What's going on? What happens? Well that's something we'll talk about in the future video. But what did we learn in this video? We learned that in asexual reproduction variations are dependent directly on the errors which are formed due to DNA copying and since these errors are introduced very slowly very minute errors each time the DNA copies the variations are very slow. It's going to take a long time for you to see changes in the structure of that cell. So basically variations are slow. On the other hand in sexual reproduction we have two parents involved and so the DNAs of the two cells of two different individuals combine and as a result the offspring gets a unique set of variations both from the mother and the father. And as a result immediately we will see offspring varying a lot from the mother and the father. The offspring will resemble them of course but they will not be clones. In other words variations become much faster in sexual reproduction. That's their major advantage over asexual reproduction.