Bozeman science: Evolution continues

hi it's mr. Andersen and welcome to biology essentials video number 9 this is on populations how they came to be through evolution how they continued to evolve every day one of my favorite theories in all of evolution is the idea of the Red Queen theory and it essentially comes from alice through the looking glass or through the looking glass where Alice remember is running around with the Red Queen and she eventually stops and says well in my country you generally get somewhere if you run as fast as you can like we've been doing and the Red Queen says you live in a slow sort of country here it takes all UK all the running you can do just to stay in the same place if you want to get somewhere else you must run at least twice as fast and so what's interesting about that is it's a really good metaphor for how natural selection and evolution takes place species are constantly in competition against all of the other organisms around them and they may not look like they're changing but they continue to change and it's shaped the life that we have on our planet and so what am I going to talk about well I'm going to start with evolution and the idea is that it's been around from day one so from day one until today all life on our planet has been created through evolution or change and also it continues on a daily basis species are evolving every day populations are evolving because remember all evolution is is is a change in the allele frequency of a gene pool can lead to speciation but it's constantly having every day one of the mechanisms by which it occurs well we've already talked about a lot of these genetic drift mutations and we'll talk more about them in the next podcast but today I want to specifically talk about selection and if you don't have a good understanding of how natural selection occurs today you're going to get it and so natural selection is when nature selects which organisms are able to survive or die and the quintessential example is in the beak of the Finch and the work of Darwin but more importantly the work of the grants sexual selection is a different type of natural selection and that's when mates are selecting based on the other gender example I'll give you as a peacock and then the one thing that I forgot to put here is artificial selection which is another important one artificial selection is another type of selection and that's actually where Darwin starts explaining the mechanisms by which natural selection could occur one thing that I want to drive home is the idea that all life evolves so once life shows up on our planet it's been evolving ever since then and so our Kia live here in the in the hot pots of Yellowstone Park and they look very similar to what the first organisms on our planet probably looked like but the archaea that live here and the animals that live in the savanna and the forest all of these things all life came from one common ancestor and they got to be the way they are through a process of evolution so let's talk specifically about the mechanisms by which that occurs and when Darwin is explaining in the origin of the species he actually starts with artificial selection because it really makes sense to us how that might occur if we were to look at this great great dane and we were to look at this Chihuahua and if we were to look at a wolf the DNA of all of them is almost identical the reason why is that these dog breeds that we have on our planet were created by humans artificially choosing traits that they want and you can see the explosion of tiny little breeds of dogs that I'm seeing around right now it's humans making those choices selecting which offspring can pass on their traits in class this year will be using brassica rapa which is a vez concent what you can do is you can actually do the selecting you can choose the traits that you want to pass on to the next generation and then you can see that our official selection taking place and actually brassica is a type of plant that led to a lot of the different foods that we have today in fact a lot of the foods that you eat were created through a process of artificial selection today I want to spend a lot of time however talking about natural selection the mechanisms by which that occurs the most famous studies on Galapagos were done by Peter and Raz Rosemary grant and they studied geophys afford asst I hope I'm pronouncing that right and they studied those on Daphne major which is this rock I've seen it from a distance it's just this rock in the Galapagos but it's a great natural laboratory so you can study the bird populations on it now natural selection is going to select species to either survive I or die and then the traits are passed on to the next generation and so here's some data from Peter and Rosemary grant 1976 they sampled all of the birds on Daphne major that they could find and they measured their beak depth in other words they measure this distance from here to here so they captured them probably annette's they measured him with a caliber and they measured the beak depth all the way across in 1976 and they done a study that 1977 and they studied the beaks for 30 years they've been studying the beaks of the the finches on the Galapagos but what they found is in 1977 there's a drought and so they go back in 1978 and so let me get the numbers right so you can see him in 1976 they sampled 751 birds so there were 751 birds here but they come back in 1978 and they found their only 90 Birds left and so lots of times when we draw these graphs you have a tendency to not realize what the N number how many species how many individuals were actually there and so what happened in that drought of 77 it's like a bird apocalypse almost all the birds died from 751 down to 90 which ones didn't die the ones that didn't die ER ones that had a slightly bigger beak and so why is that well what the grants found is that they were feeding on seeds that were slightly bigger and harder to break and so the ones that were able to break those seeds were able to survive not die and they were able to pass their genes on to the next generation and so what happened to our bell shaped curve our bell shaped curve move to the right and so we call that directional selection now are they going to stay this way no because if you have a bird a big beat you have to make that beat you have to fly it around and so when the when the weather gets good what we'll see is will actually see when there's no drought we're actually going to see it move back in the others direction or directional change and so there's moving over and over and over but that's the first type called directional selection we can also have disruptive selection disruptive selection happens when you have the bell-shaped curve of a trait and then it somehow gets split in the middle and so an example of that would be the idea that all of the birds on the Galapagos this is a pitcher that's actually from Darwin's book all of the finches on the Galapagos started from one and central species in other words there is one Finch that flew there or a population that flew there maybe 23 million years ago and the 14 beaks or the 14 species that we now have on the Galapagos Islands are actually came through disruptive selection in other words if they start feeding on different seeds you eventually can have two different species and they quit inner breeding and then you can have different varieties and so even though these look quite a bit different they all come from one common ancestor my favorite are the ones that are actually feeding on the the vampire Finch that feeds on they suck the blood off of the blue-footed boobies on the Galapagos pretty crazy last type is stabilizing selection stabilizing selection occurs when you have here's our original bell-shaped curve happens when you have selection on either side in other words you're squeezing that bell-shaped a little bit closer I couldn't come up with great example of the finches on the Galapagos of of that stabilizing selection however it would probably be what shows why one species stays the same but a great example of this would be in the birth of children in other words if you are a tiny baby let's say back in the day you weighed one pound when you were born you probably were born premature and you died if you were like 18 pounds as a baby you probably didn't get out of your mother and you died and her genes died with you and so that's going to push that bell shaped curve together so that's artificial selection excuse me natural selection and then the last type is going to be sexual selection sexual selection it was come up with by Darwin as well but not really tested until until the 19th century or the 20th century in sexual selection the maid is actually doing the choice and lots of times we'll see sexual dimorphism in other words this is a peahen and this is a peacock and so we see a huge difference in their appearance and the reason why is that the female is making the choice it's not nature that's making the choice she's actually making the choice and so why does a peacock have this beautiful train that it does it's just going to get in the way it's doing that to impress the mate in other words this female is only going to choose a peacock that has a really big train now why is she doing she's looking for herself she's only going to choose a trait that's going to pass on or it's a clear indication of the health of that mate and so if you can make a beautiful train like this you probably have good DNA and their word studies done where they would actually eliminate so they would cut off some of these eyes and they would find the female the P hands would actually ignore them they also found in the studies that if the mate if the males have a really beautiful train like this they actually produce offspring that are more likely to survive and so in sexual selection the females actually doing the choice not doing not nature and so if we ever see that sexual dimorphism so like a Montana we have elk and the elk have these huge antlers but they're doing that to impress their me now Jeffrey Miller has taken this to an extreme not to an extreme but he's saying that what is it in humans that is like the Peacock's feathers what is it it's like that in us that's just it's it's grossly in excess what we would see in humans is that it's our brain it's how smart we are and why are we so smart well we're trying to impress females and so it's it's interesting when you look at males and ask them what what are they attracted to in females a lot of time its physical characteristics but when you ask females it's more behavior he makes me laugh or he makes me feel good and so those things are clear indications of brain and Jeffrey Miller will go as far as to say that culture and all of those things are just made through process of sexual selection I think he's headed in the right direction