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  • Hi. It's Mr. Andersen and welcome to Biology Essentials Video Number 2. This

  • is examples of Natural Selection. In the first video I talked specifically about what natural

  • selection is and how it can affect a gene pool. In this one I am going to talk about

  • real world examples of evolution and natural selection taking place right now. I wanted

  • to start by showing you this picture of Glacier National Park. What's interesting and a little

  • sad about Glacier National Park is over the next few years all of the glaciers will actually

  • melt. And the reason why is that the Earth is getting warmer and as a result of that

  • it's impacting the glaciers and it will impact the living things in Glacier National Park

  • as well. So these right here are glacier lilies that come out right after the snow moves away.

  • And so plants across the world are having to adapt to these changing climates. So that's

  • an example of real world evolution. I always like to start with kind of an overlay of what

  • we are going to talk about in this podcast. Natural selection, remember, causes evolution.

  • What's neat about it, it's different then random events that cause evolution. What's

  • interesting about natural selection is it actually creates organisms that are better

  • adapted to their environment. So the first thing I am going to talk about is how changes

  • to the environment, especially climate changes right now are affecting life on our planet.

  • Next I want to briefly talk about how mutations can cause changes in phenotypes and those

  • gene changes can have huge implications when it comes to organisms. Some of those make

  • big phenotype or physical changes. Some don't make any changes at all. Next I'll talk about

  • how those phenotypes or those changes can actually affect the fitness of organisms.

  • And so there was one mutation in the protein that makes blood that actually created sickle

  • cell anemia. And that was bad but it also saved millions of lives in protecting them

  • from malaria. And then finally I want to talk about another environmental change and that's

  • the environmental change that is humans and how we're impacting evolution on the planet

  • right now. A really scary example of that would be antibiotic resistant bacteria. Bacteria

  • that were once curable but aren't anymore. And so that's what I am going to talk about.

  • I wanted to start with poet naturalist Henry David Thoreau. What's interesting about him,

  • he lived on Walden Pond and if you have read any of his work it's really inspirational.

  • He's an amazing writer. But what's interesting is we're actually able to use some of his

  • work to show evolution and natural selection taking place. Because most people know that

  • he was a writer, but most people don't know he was a naturalist as well. And so he would

  • study, for example, St. John's wart and blueberries. And he would detail when they would flower

  • and we can use that data to show how climate is actually affecting plants. And so here's

  • a quote where he's talking about, in 1853, how the blueberry buds were starting to come

  • out. And we have a date, and so we can actually look at that. And so let me give you an example

  • of that. So let's say we've got the blueberry and it is flowering on the seventh of April

  • back in 1853. So if this is 1853. Now maybe this is the first blueberry, but this bell

  • shaped curve represents when all the blueberries on Walden Pond were coming out. Now if you

  • were a blueberry and you were to come out earlier than that, there would probably be

  • snow. There wouldn't be anything to help you flower or to transfer that pollen. And if

  • you were to come out later than that then you probably wouldn't survive as well. And so the average

  • blueberries would probably start to flower around the early part of April. Now what's

  • happened since then is that the climate has changed. And so if we look now in 2011, it's

  • going to be much warmer on April 7th then it was in 1853. And so the blueberries that

  • were able to come out a little bit earlier have done fine. And so if we were to look

  • at the bell shaped curve of blueberries today, we would find that it is probably shifted

  • quite a bit and things are flowering earlier just because the climate is getting warmer

  • and warmer. And if you were a blueberry right now and to flower really really late you'd be behind

  • the ball. You'd be way behind and so what we've seen is directional selection. In other

  • words that bell shaped curve has moved. Nice thing about the work of Thoreau is that we

  • can actually quantify that because we can see what days it's changing today. Next I

  • want to talk specifically about phenotypes. Remember phenotypes are going to be the physical

  • characteristics that you have but remember all changes, all novel changes in organisms

  • comes from changes in their DNA. So when we get changes in the base pairs, or in the bases

  • inside that DNA, that eventually leads to things like the way we look. So this is a

  • type of mollusk. It's the Donox variabiliis. And it has a number of different patterns

  • that come from one species of mollusk. These ones live in the sand and you can see how

  • genes have added this striation and then it also looks like there's a gene that's adding

  • these vertical striations as well. And so those phenotypes started as a mutation, or

  • a change in the DNA, but it ends up changing the physical appearance. And if it wasn't

  • for all of this variety, all of these different types of shells then natural selection wouldn't

  • work. In other words, if all organisms look the same then there's nothing for them to

  • select. Okay, let me talk about an example of this found in humans. This right here is

  • the most dangerous animal that we have on our planet, the anopheles mosquito. And the

  • reason it's dangerous is it passes the disease called malaria. And you can see where malaria

  • is found in subsaharan Africa. It's killed millions and millions of people. Now we would

  • say thousands of years ago, I can't remember on the specific day, there was a mutation

  • in one person who lived maybe in Africa. And that mutation caused a red blood cell that

  • normally looks like this to be made like that. It's a change in one letter of the DNA which

  • affects the hemoglobin protein inside the blood. And so you get a sickle shaped red

  • blood cell. Now this is very painful if you're sickle cell anemic. It causes organ failure.

  • It's a really bad disease to have. What's interesting about it is if you are heterozygous

  • for that, in other words, if you have two genes for it you're going to have sickle cell

  • anemia, but if you only have one, you can't get malaria. So you're protected from malaria.

  • And so here we had one mutation which caused one phenotype change, or one change in the

  • blood which protected them against malaria. So what we see is natural selection in humans.

  • In other words this is where sickle cell gene is found, so right here in the darker areas,

  • greater than 20% of the people have that sickle cell gene and the reason they do here is that

  • they're protected against malaria. But again, if you lived here, and you have that sickle

  • cell disease where malaria is not present, that would actually be a negative. And so

  • you can see how natural selection is at play. But first you had to have that mutation, first

  • you had to have that change. Last thing is kind of a warning call and humans are starting

  • to figure out that we can really have huge impacts on the organisms that live on our

  • planet. And the example here that I am talking about is tuberculosis or TB. Tuberculosis

  • has killed humans for years and years and years. This would be a good way to diagnose

  • it. You look at a chest x-ray and you can see that the bacteria are actually feeding

  • on the lungs. And this would be the bacteria right here. They're a rod shaped bacteria.

  • Tuberculosis has been around since humans, pretty much way back in the day of the pharaohs,

  • we had tuberculosis. And so what we did is we discovered that you can kill tuberculosis

  • using antibiotics. And so if somebody has tuberculosis, we give them antibiotics, it

  • kills all the bacteria except those that are highly resistant. We then take another dose,

  • we take another dose and if we quite taking it, what we end up with, if we can't kill

  • all of the bacteria, is we end up with highly resistant bacteria. And so we've created a

  • disease, multi drug resistant tuberculosis, and what that is, is a form of tuberculosis

  • that is resistant to sometimes a dozen different antibiotics that humans have created. And

  • so that's a human made problem. And so who is doing the selecting? Well, we are. And

  • that's why it's important when you take antibiotics, that you don't take them unless you really

  • need them. And when you do take antibiotics, that you take them until the course has run

  • its . . . all the way through. We are seeing some nasty types of multi drug resistant tuberculosis.

  • This person is actually being treated in Russia where lots of times they don't get complete

  • treatment and were just spawning this disease as they get worse and worse. The sad part

  • about that is all these diseases that we once had a cure to, we don't anymore. And the reason

  • why is that natural selection and us are actually creating this problem. And so those are some

  • examples of natural selection and evolution and I hope that's helpful.

Hi. It's Mr. Andersen and welcome to Biology Essentials Video Number 2. This

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自然選択の例 (Examples of Natural Selection)

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    Jan に公開 2021 年 01 月 14 日
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