Darwinism vs. Social Darwinism part 1 | US History | Khan Academy

Hey, this is Kim from KH Academy. I am the history fellow here, and I am here with Emily.

Hi, I'm the biology fellow. So, Emily and I are here talking about Darwinism, and I'm interested in Darwinism because in the late 19th century, we usually call the Gilded Age, there is a very prominent interpretation of Darwinism that is called Social Darwinism.

Social Darwinism wasn't so much an actual form of biology as it was kind of a misinterpretation of how natural selection and the theory of evolution worked. That was used to justify or explain a lot of the social inequalities of this time period. The way people often thought about it was that white Anglo-Saxon people, so Europeans, Northern Europeans, were kind of the most evolved. This is our timeline of evolution from least evolved to most evolved.

People like African-Americans or Asians or Native Americans, or even Eastern Europeans, were less evolved; that they were on a scale of evolution where they hadn't come as far as Anglo-Saxons. So Emily, you're a biologist, and I would love to get your take on how it is that natural selection actually works and how this doesn't quite describe what was really going on.

Emily: Yeah, definitely. So maybe I can speak first to that specific graph that you've drawn. I think that this is actually a common point of confusion when it comes to evolution: that there's not really such a thing as more or less evolved in evolution.

Okay, so this gradient really doesn't exist.

No, I mean there's, um, there's sort of the—I think that people sometimes see the pictures of like the ape standing up and turning into a person, and they think, "Oh, this is sort of a linear path from one thing to another." But what you really get is different types of organisms evolving from a shared ancestor and branching off.

So, all right, so nobody who's alive on Earth today has been evolving for more or less time since their last common ancestor on than anybody else.

Kim: So would you—I'm going to draw what I think is how you're explaining this, and please correct me as I go along—but say this is my common ancestor, and then would there possibly be branches like this?

Emily: Yeah, that's a great way to draw it. I mean, you know, certainly humans are all extremely closely related to each other. But like we could even say this for us versus a dog, a bacterium—like pretty much anything—all life on Earth shares a common ancestor.

So that bacterium is just as evolved as you are, actually, in the sense of absolute time since those two split apart. Right? So like from the moment that life first appeared on Earth, there has been so much time, and all of us have been evolving from that point.

So even whether you're a piece of bacteria—piece...a good word—a bacterium, there you go, bacterium. I took biology once. Or you are Albert Einstein, you have been evolving for precisely the same amount of time.

Kim: Wow, I'm really relieved to find that I could describe that as well.

Emily: Good, you did a great job! Beautiful!

Um, so okay, so you've done this distinction between evolving from a common ancestor. So how is it that the actual theory of natural selection works?

Emily: Yeah, that's a great question. So natural selection, often people talk about it as sort of having three key ingredients. And to see how it works, let's imagine that we're just looking at a population of beetles. So, picture your beetles to start with.

And what would we need to have in order for these beetles as a group to evolve by natural selection? One thing that we would need is we would need some variation among the beetles.

Okay, so if you have identical beetles, you're not going to have any that are better at surviving or reproducing than any others, which is kind of a key ingredient for what we're going to talk about.

Kim: Okay, so I've got two different beetles here; they're slightly different from each other.

Emily: Awesome! And you've made them different colors, which is perfect. So we have variations. And the next ingredient that we're going to need is we're going to need that variation to be heritable. So we're going to say that those beetles, one of them is green and one of them is blue, and that's because of something in their DNA.

So they have differences in their DNA that create the variation in colors.

Kim: Okay, so all right, so when you say heritable, you mean that this is something that their descendants could inherit?

Emily: Exactly! That is exactly it. So the final ingredient is that the differences—these heritable differences—need to affect how good the beetles are at leaving offspring in the next generation.

Kim: Okay, so for example, let's say we would probably have more than two beetles in our actual population, but let’s say this population has just moved into a new area that is very blue-colored.

So blue rocks, blue flowers, whatever. And there’s also a bunch of birds in that environment that really like to eat beetles. And I'm guessing that if they have blue beetles and green beetles, that one of those is going to show up a lot better against the blue environment than the other.

So probably a lot of our green beetles are going to get picked off by birds, and they're not going to be able to leave offspring because, gosh, they kind of got eaten.

Emily: So when you look at the next generation of beetles, if we know that the colors get passed on, we're going to probably see a bigger proportion of that group being made up of blue beetles and less being made up of green.

And that is an example of natural selection in action where you can see that organisms that survive and specifically reproduce better in a certain environment are going to increase in frequency in a population. So you're going to get more and more of these blue guys and less and less of the green guys.

Kim: Is there a word you would use to describe this sort of—a sort of adaptation? Is that the natural selection part?

Emily: Adaptation is a good word to use—as from variation and heritable. Natural selection is just the differential survival and reproduction.

And as you mentioned, a great word there, which is adaptation. Adaptation is the word that biologists often give to the process of a population getting better and better suited to its environment.

So you would say that the population was adapting to being in a blue space as it gradually started to have more and more blue beetles across generations.

Kim: So what I find really interesting about this is that it's entirely by chance, right?

Emily: Um, more or less. You've got a genetic mutation, and then that mutation happens to suit the environment that you're in, which allows you to thrive and your genes and your adaptations to be passed on over time.

Kim: Yes, and I mean the variation would have occurred randomly to start with—like you say, it would have been a mutation. It didn't happen because the beetles went to a blue place and said, "Gosh, I should be blue; that would be awesome!"

That was not what happened. That it was already there, and it just happened to be successful in that environment.

And if they'd gone to a green place, well, guess what? You would have gotten exactly the opposite effect. Suddenly the green guys would have been more successful, more able to leave offspring, and you would have seen green increasing or, quote unquote, favored by natural selection.