I hope you enjoyed the video from stated clearly on natural selection and I want to summarize just some of the key points for you that are critical to our understanding of bacteria you know evolution is going to be a theme in our class because you can't understand much about life without understanding it in the context of how life changes and evolves so all living things have a common ancestor so we talked about Luca the last Universal common ancestor in a prior lecture segment here as these living things reproduce and they create new generations they make babies the new generations are always a little bit different than the original ancestor and as you get generation after generation after generation changes begin to accumulate and after a while the ancestor is going to be very different than the original the new organisms can be very very different than the original ancestor one thing that's really important to note is that most changes are detrimental so the vast majority of changes are either detrimental which means that they actually harm the organism or they don't have any effect at all if an organism is less fit to survive then a genetic change won't be is much less likely to be transferred to a new generation because that organism that has a detrimental change is less likely to reproduce and you have to be able to survive and reproduce an order for genetic changes to be passed on very occasionally a modification gives the descendant an advantage and so if you have a gene that gives you an advantage in terms of surviving and reproducing then you're more likely to pass that change on and over a few years this usually doesn't have a huge effect but over billions of years what we've seen is this population of diverse life on Earth adapted to essentially every situation that you can imagine with a few exceptions now I want to remind you if you didn't pick this up from the video that there are two forces occurring in evolution the first force is genetic change so this is the random changes that occur as organisms reproduce genetic changes random there is no there is no specific process by which genetic change occurs that results in some changes happening and other changes that it's a random process however the selection of the genetic changes that confer advantages that's actually not random because a change is an advantage only if it helps you survive in the environment that you live in so for example if you are an animal and you have ended with a genetic change that results in blood vessels being closer to the surface of the skin now it might give you a great advantage in a desert environment where it's hot and you need to cool off but might be incredibly detrimental in a cold environment where it's very very freezing cold and you need to keep your blood closer to the core of your body to stay warm so there the genetic change is is random mistakes happen in DNA it's a random process but the selection of traits for being advantageous or disadvantageous to survival and reproduction that's actually not random that's going to depend on the environments animals are in and plants and bacteria and whatever form of life we're talking about so we refer to the three types of mutations and again I want to emphasize mutations are random these mutations can result in a beneficial outcome that's rare they can result in a neutral outcome that can be quite common and it can be detrimental which is also common typically when mistakes are made in DNA it doesn't end up being a good thing it's usually either has no effect or causes big problems for the organism alright so just a little overview bit of natural selection you know we don't think of individuals evolving I always talk about how my husband is evolved since we've been married but actually you know that's a behavioral change right but populations evolve so we think about genetic chain over many organisms and large populations that that's the process of evolution evolution doesn't have an end goal we like to think I think because we are a complicated and intelligent species we like to think we are anyway that maybe evolution is sort of sometimes people show evolution as a ladder where each organism gets more complex and has more abilities than the next organism that's actually the only reason that we are smart and able to build buildings and all the amazing things that humans do is because that's given us an advantage and so those traits have been selected for because they've allowed us to if you think about it live everywhere on earth right and and be more successful than any other animal so evolution doesn't really have an end goal new traits that give you an advantage are selected for and if you think about climate change again you know if the earth gets so warm that humans are unable to survive bacteria will be fine right we've said this before so we can certainly deselect the environment could certainly deflect for humans and then select for other similar organisms if the situation changed radically environment is what specifies what's advantageous if the environment changes then what may have been an advantage before might not be an advantage any longer and an advantage in one environment might be different than an advantage in another environment sort of thinking of you know the north pole in the Sahara Desert is good examples of two extremes all right so that's sort of an overview then of natural selection now we've talked about where life may have how life may have originated on earth and the evidence for the presence of life on Earth and then a little bit about how life has changed during the period that it's been on earth we want to talk about how scientists organize life into related groups that'll be our next topic