[Music] I'm welcome back to free sighs lessons Kol UK by the end of this video you should be able to describe what's meant by evolution you should then be able to explain how evolution takes place through natural selection now the earth is teeming with living organisms and I'm showing you a tiny function here we've got large animals such as mammals and fish and smaller animals such as insects we've also got plants such as ferns and trees there are nearly 9 million different species of animals and plants on the earth and that number does not include microbes such as bacteria it's also thought that all these species have only one percent of the total that have ever lived on earth all of the rest are now extinct so the question is where have all these different species come from scientists believe that life first developed on earth more than 3 billion years ago these first life-forms were very simple for example single cells all species of living things have evolved from these simple life forms scientists call this process evolution by natural selection and we're looking at that in this video you need to be able to describe this process in the last video we saw that there's a massive amount of genetic variation within a population of a species a good example is with rabbits but this could apply to any species every rabbit will have a slightly different combination of alleles that it inherited from its parents some rabbits will have alleles for thicker fur some rabbits will have allele for better eyesight and some garbage will have alleys for better hearing now imagine that the environment gets a lot colder rabbits which of inherited alleles for thicker fur are more likely to survive the colder temperatures than rabbits with thinner fur so because the rabbits were thicker fur can survive the cold they're more likely to go on to reproduce their offspring could inherit the alias for thicker fur and these offspring are also more likely to survive the cold and reproduce scientists call this process natural selection over many generations the alleles for thicker fur will become more common among the population of rabbits and overall the rabbit population will tend to have thicker fur than before let's look at a different scenario imagine that a predator moves into the area for example a fox now the Roberts which have the alleys for better eyesight or better hearing have an advantage these rabbits will be more likely to detect the Fox as it approaches then rabbits which do not have the alleys for better eyesight or better hearing so rabbits with better eyesight or hearing are now more likely survive and reproduce and the beneficial aliens may be passed on to their offspring over many generations the alleles for better eyesight or better hearing will be widespread in the rabbit population in both of these examples scientists say that population of rabbits has evolved I'm surely the definition of evolution here evolution is the change in the inherited characteristics of population over time through a process of natural selection now sometimes two populations of one species can't become so different and phenotype that they can no longer interbreed to produce fertile offspring these two populations have now become two separate species I'm showing that here with rabbits the rabbit on the left is normal-sized the rabbit on the right is a pygmy rabbit pygmy rabbits are so small that they cannot breed successfully with normal-sized rabbits so that means that pygmy rabbits are with different species now if you don't triple biology then you'll be seeing speciation in more detail in a later video remember you'll find plenty of questions on evolution by natural selection in my vision world book and you can gather by click on the link above [Music]