in today's video we're going to see how the differences in both our genes and our environment can lead to huge variation between different individuals and how over time this can lead to the evolution of new species by a process we call natural selection if you take a look at a group of individuals in a population you'll notice that they're all different and in biology we call this variation as each individual has different phenotypes if you remember a phenotype describes the observable characteristics of an individual due to the interaction of two things their genes and their environment genes code for proteins and a genome which is all of your genes combined codes for an entire organism apart from identical twins everyone in the world has a unique genome which means they have slightly different combinations of proteins inside them and so they look different the way we look and function though isn't just due to our genes it's also due to the environment that we're exposed to for example a pair of identical twins may have the same genes for being tall but if one of them didn't eat or sleep as much as the other then they might not be as tall or if one of them spent more time in the sun than the other then their skin would be darker the key point to remember with all of this is that most of our characteristics are determined by the interaction of our genes and our environment in fact most of our traits are influenced by lots of different genes and lots of different environmental factors now the fact that there are so many different environmental factors kind of makes sense we all do different things eat different foods and so on but why is there so much genetic variation well the reason there are so many different genes is because of mutations a mutation is a change in the DNA code so that the protein that it codes for may be different keep in mind that most mutations don't actually have any effect on the proteins and so don't change the organism's phenotype at all however in those cases where mutations do change proteins the phenotype may change slightly this change will usually be something bad and unwanted but very occasionally the mutations are beneficial for example they could make us more resistant to lung disease or give us the ability to run faster now as you can imagine these beneficial mutations mean that those individuals who have them are more likely to survive and so they're more likely to be able to reproduce and pass on their genes to the next generation this idea that the fittest individuals are more likely to survive was noticed by Charles Darwin in the 1800s and he called it survival of the fittest at the time he didn't actually know anything about mutations or genes but he did notice that certain traits were being passed on from parent to child and that the most useful traits were passed on the most he called this natural selection as the fittest individuals were being selected to survive his most important thought though was the concept of evolution which described how the inheritance of certain characteristics in a population over multiple generations could lead to changes in the whole species or sometimes even the development of an entirely new species this means though that all current species must have evolved from different species sometime in the past and if you take it back far enough we can see that the theory of evolution by natural selection implies that all living species must have evolved from the simple life forms that first developed more than 3 billion years ago just like countless other important theories it took a really long time for Darwin's theory to become properly accepted by the scientific community but it's now been proven multiple times over from things such as the development of antibiotic resistance in bacteria where we can literally see evolution taking place or by looking at fossil records as we'll see in other videos so in summary evolution occurs through natural selection of certain genetic changes that give rise to the phenotypes that are best suited to the environment and given enough time the phenotypes of two different populations within a species may become so different that they can no longer interbreed to produce fertile offspring at which point we can say that a new species has been formed if you haven't heard yet you can find all of our videos on our website cognito.org you'll also find questions flashcards exam style questions and past papers and we track all of your progress so that you always know what to study next so sign up for free by clicking here or browse our playlist here on YouTube