So evolution is this process through which variation in individuals, so different phenotypic variation, makes them more likely to survive and reproduce. And so, there are three principles to how this happens. The first is that variation. So individuals within a population have some type of variation, and I think we would all agree that this is true. We see it in humans, not everyone is the same. We see it in birds, not every bird is the same. See it in every organism on Earth that there's variation that exists in that population. So it's the first principle. The second is heredity, and that is that offspring resemble their parents more than they resemble unrelated individuals. So that is because genes are passed on to the offspring, so that variation can be passed on to the offspring. Everyone, I think, will agree with this. And then third is selection, and that is that some variation, so some of these forms, specific variation is more successful at surviving and therefore, reproducing than other forms. So it's the variation that exists that we all see. Some of it all is inherited in the offspring, and some of that variation allows for those particular individuals and then their offspring to be more apt to survive in the condition at a time. So here is an example of Darwin's finches that he studied. We can definitely see variation in beak size, maybe an eye size, and head size. If we were to look at the offspring of these, finches, we would see that those offspring, the offspring at number 1 is going to resemble number 1 more than it would resemble 2, 3, or 4. And then finally, selection. This variation potentially for number 1, because it has a bigger beak, it's able to break maybe harder nuts or seeds in order to get that food. So potentially, it could survive more. And that would be an example of selection. It's really just what evolution is. It's variation that's inherited and then selected for. Now there's a theory of evolution that is the neutral theory.
And this states that evolution isn't necessarily caused by one mutation that's been that's very positive and leads to this huge increase in fitness and survival and reproduction. But instead, that most evolution is caused by genetic drift of neutral mutations. So you may say, okay, let me let me think about this. What is genetic drift? Remember, genetic drift is that random just passing on of random alleles, of these different alleles in the population. It can lead to fixation. It can be lost. But, essentially, it's just the random selection of alleles that are passed on to the offspring because the number of offspring produced isn't infinite. So the number of offspring only has a selection of the alleles in the gene pool. That's genetic drift. But a genetic drift of neutral mutations, neutral mutations are mutations that have no effect on the amino acid. So these are also called synonymous mutations, and this can change one codon to an alternate codon, and therefore there's no change in the amino acid produced, and therefore no change in the protein that's made. However, a mutation was there. And so how, and then the opposite of that is the non synonymous mutation, which causes a change in amino acid. Now, Now I think we would all agree that the majority of the mutations that happen in an organism are neutral. Right? They're mostly happening in introns. They're not affecting the protein. Because most of the time, if you're affecting the protein, it's harming it and, therefore, it leads to death of the organism and therefore, it's not selected for, that offspring isn't produced. And so, the majority of the mutations that are created are neutral. And therefore, the majority of evolution that takes place happens because genetic drift randomly selects for these, neutral mutations, just kind of randomly. And that can lead to divergence of different species and evolution of the organism as a whole. Now there are two ideas of how different types of mutations, both neutral and then positive or negative mutations that occur, can lead to evolution. The first is single step, and that means that there's a single step.
So there's one mutation, multiple mutations, this random mutation, and it just happens all at once, and that causes the selection for that trait. It's beneficial. It allows it to retain in the environment and all happens in a single step. Cumulative selection takes is different and that multiple single steps are accumulated over time, and that leads to selection for the trait. So the best way to explain this is using the infinite monkey hypothesis. And what this has, and you probably heard about it before, right, is that, if you set a monkey down at a typewriter, it's kind of an old hypothesis, typewriters. But you set a monkey down at a typewriter, and you just let them push random buttons for an infinite amount of time. Eventually, at least one of those times, the monkey would write the complete works of William Shakespeare. And it's just by chance. Right? If you let the monkey type every single combination of letters just randomly, At least one of them is going to be William Shakespeare's works, just by random. So if we look at this and compare it to evolution, single step selection says that, okay, well, if the monkey is typing one of those times, it'll happen at once, and the monkey will if we let it sit there long enough, it's huge, I mean, Cumulative selection for evolution Cumulative selection for evolution says that, okay, well, we think that that maybe takes too long to just wait for that monkey to just randomly do that in one single step. So what we're gonna have the monkey do is instead, we're going to set the monkey down and we're gonna let it write 50 works that are as long as William Shakespeare. Once it's written 50, we're going to have someone come in and pick which one is the best, that best represents William Shakespeare's work. Then, when we have that best one, so this is the process of selection, so we have all these different organisms that are made and selection chooses that best one. Then, the monkey is given that best one and allowed to improve on it to make it more like William Shakespeare. And it does this over multiple times that are accumulated. So each round, 50 are typed, and then somebody comes in and chooses the best one. So that somebody comes in and choosing it, that's natural selection coming in and choosing which one is most like William Shakespeare or which organisms more likely to survive. Then you do that for 1 round, 2 round, 3 rounds, 4 rounds, 10 rounds, 50 rounds, and it starts looking more and more like William Shakespeare, even though it's the same process that's happening every time. So finally, at the end of however many rounds it takes, 70 rounds, a hundred rounds, a thousand rounds, that you do get this work of William Shakespeare. But it takes much less time because natural selection is coming in and selecting for each round which one is the best or which organism is gonna survive best. Whereas in single step selection, it all just, if you wait long enough, it'll happen. Right? If you wait long enough for that monkey to type one, at least one time, it'll be the random words of William Shakespeare, but it's going to take a long time to let that monkey try all the different combinations that it can before it types that work. Whereas cumulative selection, natural selection's coming in, it's sort of selecting each round or each generation, which one is the best, and that eventually will lead to the complete works of William Shakespeare in a much less time consuming manner. So those are really the 2 main ideas. Obviously, a lot of people prefer cumulative selection, but there is, some evidence that, you know, these single step selections do and can happen as well. But it's not just that one is right and one is wrong, but that they're both acting to promote evolution. So with that, let's now move on.
