- [Voiceover] Hey, this is Kim from Khan Academy.
I am the History Fellow here, and I am here with Emily.
- [Voiceover] Hi, I'm the Biology Fellow.
- [Voiceover] So, Emily and I are here
talking about Darwinism.
I'm interested in Darwinism,
because in the late 19th century,
usually called 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,
and 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.
- [Voiceover] Yeah, definitely.
So, maybe I can speak first to that specific graph
that you've drawn on.
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.
So-- - [Voiceover] Okay, so,
this gradient really doesn't exist.
- [Voiceover] No, I mean, 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."
What you really get is different types of organisms evolving
from a shared ancestor, and branching off.
So--
- [Voiceover] All right so--
- [Voiceover] Nobody who's alive on Earth today
has been evolving for more or less time,
since their last common ancestor,
than anybody else.
- [Voiceover] So would you,
I'm gonna draw what I think is how you're explaining this,
and please correct me, as I go along.
Say this is my common ancestor,
and then would there possibly be branches like this?
- [Voiceover] Yeah, that's a great way to draw it.
Certainly, humans are all extremely closely related
to each other,
but we could even say this for us,
versus a dog, a bacterium.
Pretty much anything, all life on Earth,
shares a common ancestor.
That bacteria is just as evolved as you are, actually,
in this sense of absolute time,
since those two split apart.
- [Voiceover] Right, so 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.
Even whether you're a piece of bacteria,
piece a good word?
A bacterium?
- [Voiceover] There you go! - [Voiceover] Excellent.
- [Voiceover] Beautiful. (laughs)
- [Voiceover] So bacterium.
I took biology once,
or you are Albert Einstein.
You have been evolving for precisely the same amount
of time.
- [Voiceover] Yep. - [Voiceover] Awesome.
Okay, wow, I'm really relieved to find that I could describe
that as well as I could.
(laughs)
- [Voiceover] You did a great job.
Beautiful.
- [Voiceover] Okay, so you've done this,
this distinction between evolving from a common ancestor.
How is it that the actual theory of natural selection works?
- [Voiceover] Yeah, that's a great question.
So, natural selection, often people talk about it
as sort of, having three key ingredients.
To see how it works, let's imagine that we're just looking
at a population of beetles.
So picture you're beetles, to start with.
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.
- [Voiceover] Okay.
- [Voiceover] 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 gonna talk about.
- [Voiceover] Okay.
So, I've got two different beetles here.
They're slightly different from each other.
- [Voiceover] Awesome.
You've made them different colors, which is perfect.
We have variation,
and the next ingredient that we're going to need,
is we're gonna need that variation to be heritable.
We're gonna say that those beetles,
one of them is green and one of them is blue,
and that's because of something in their DNA.
They have differences in their DNA,
that create the variation in colors.
- [Voiceover] Okay.
Alright, so, when you say heritable, you mean that this
is something that their descendants could inherit?
- [Voiceover] 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.
- [Voiceover] Alright, okay.
- [Voiceover] For example, let's say,
we would probably have more than two beetles,
in our actual population --
- [Voiceover] Okay.
- [Voiceover] But, let's say this population has just moved
into a new area that is very blue colored.
- [Voiceover] Okay.
- [Voiceover] So blue rocks, blue flowers, whatever.
There's also a bunch of birds in that environment
that really like to eat beetles.
- [Voiceover] Oh.
- [Voiceover] I'm guessing,
that if they have blue beetles and green beetles,
that one of those is gonna show up a lot better
against the blue environment, than the other.
Probably a lot of our green beetles are gonna get
picked off by birds, and they're not gonna be able
to leave offspring, because gosh, they kinda got ate.
(laughs)
So, when you look at the next generation of beetles,
if we know that the colors get passed on --
- [Voiceover] Mm-hmm.
- [Voiceover] We're gonna probably see a bigger group of,
a bigger proportion of that group,
being made up of blue beetles,
and less being made up of green.
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.
You're gonna get more and more of these blue guys,
less and less of the green guys.
- [Voiceover] Is there a word you would use
to describe this, sort of, this adaptation?
Is that the natural selection part,
as from variation, inheritable?
Like, the natural selection is just like a good situation?
- [Voiceover] Yeah, I mean, natural selection is really,
just the differential survival and reproduction.
As you mentioned a great word there, which is adaptation.
- [Voiceover] Mm-hmm.
- [Voiceover] Adaptation is the word that biologists
often give to the process of a population getting
better and better suited to its environment.
You would say that the population was adapting to being
in a blue space --
- [Voiceover] Mm-hmm.
- [Voiceover] As it gradually started to have more and more
blue beetles, across generations.
- [Voiceover] What I find really interesting about this,
is that it's entirely by chance, right?
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.
- [Voiceover] Yes!
I mean, the variation would have occurred randomly
to start with.
Like you say, it would've been a mutation,
it didn't happen 'cause the beetles went to a blue place,
and said, "Gosh, I should be blue, that would be awesome."
That was not what happened.
It was already there and it just happened to be successful
in that environment.
If they'd gone to a green place, well, guess what?
You would've gotten exactly the opposite effect.
Suddenly, the green guys would've been more successful,
more able to leave offspring,
and you would've seen green be increasing or,
"favored by natural selection."