All language subtitles for 5700xLec01Sec05Evo-en

Second thing we're not doing-- and this pains me--

we are not going to give real justice

to the whole tree of evolution.

There is stunning information we have about how life

has evolved on this planet.

That is an evolutionary tree of life starting way back

here billions of years ago when life was not so diverse

and, as time goes on, radiating out and out into more branches

from bacteria to more complex things, plants, fungi, mammals

over here, you over there.

I wish we could describe all of this amazing evolutionary

history.

We're not going to.

But I hope you'll be interested enough

to ask, how was this all possible?

How did it all happen?

And you'll be able to understand based

on some the things we've talked about more about evolution

afterwards.

I'll give you, for the moment, a few red letter

dates to remember.

Here are a few important dates to remember just for reference,

because I think it's kind of interesting.

4.5 billion years ago-- I'll write

B-Y-A-- the Earth was formed.

That's an important date you should remember.

4 billion years ago, that hot planet

at incredibly high temperatures over here,

which couldn't possibly have supported anything,

cooled down.

The Earth cooled down enough that it was even conceivable

that a living organism could exist on it.

Now, what I find amazing is that 3.7 billion years ago,

the first life was present on Earth.

Within 0.3 billion years, 300 million years,

the first life evolved on Earth.

Simple bacteria-like cells, what we call prokaryotic cells,

evolved.

That says something.

That says, somehow it wasn't so hard to evolve life.

There must have been simple principles underlying it that

somehow let life get going.

Recognizable cells exist within the first 300 million years.

Now, what's equally mind blowing is

that it took almost another 2 billion years, 2 billion years,

to the 1.5 billion years ago point

that the first nucleated cells, what we call eukaryotic cells

with a true nucleus, evolved.

That says it took a mere 300 million years

to evolve life in the first place

but another almost 2 billion years

to be able to evolve a nucleus.

Seems a little strange, doesn't it,

that it took that long to make that innovation of a nucleus.

Now, of course, there's a big difference.

The first cells had no competition.

They didn't have to be better than anything.

The second innovation like a nucleus

had to be better than everything else that

was already in the ecosystem.

So that explains perhaps why it takes that much longer.

Now, it's another 1 billion years

before we get at about half a billion years ago

to multicellular life.

It took some real work to have multicellular organisms

with whole body plans, complex body

plans like the sort of things you might recognize today.

So that was another amazing innovation.

And all that's happening much later in this picture.

The next relevant date for students

is probably 0.005 billion years ago.

That is 5 million years ago, which was

the first human-like creatures.

Humans, broadly writ not Homo sapiens, go back there.

The first Homo sapiens, about 0.0001 billion years ago,

we have Homo sapiens.

You're a pretty recent arrival in this picture.

And finally, the last important date to remember is 0.0000002

billion years ago, MIT was founded.

Roughly speaking, that's a history of life, all right?

I obviously leave out some details and arguably

overemphasize others.

But in any case, from our perspective here,

that's roughly a history of life.

We're not going to really go into much more than that.

But I want you to have a framework

to think about pretty some of those amazing innovations

and how all those came about.

And the secrets of life that we're

going to talk about mostly were worked out here.

Those secrets of life were already present

just 300 million years after the Earth cooled.

Other things that we're not going to do justice to,

and I wish we could do justice to, but truth in advertising

requires me to tell you that we're not

going to do full justice to them, cell biology.

Cell biology, well, wow, cells are pretty amazing.

We're going to talk, as I've already talked about,

about eukaryotic cells, and prokaryotic cells, here

bacteria, here animals, plants, fungi.

These, as I've drawn them, tend to be

kind of small, 1 to 2 microns in size,

these much bigger typically, 10 to 40 microns in size.

But some of them can be much bigger than that.

They can be much bigger than that.

These have a nucleus in which their DNA is nicely

packaged up.

These, for the most part, do not.

I mean, these do not have a nucleus.

Their DNA is not organized in a nucleus.

These have all sorts of wonderful complex organelles

to whom we are not going to do just at all.

We could look richly at these cells here.

Here's a prokaryotic cell, a little bacterial

with a little flagella tail.

And it's got its DNA kind of messed around here in its cell.

It doesn't have a nucleus.

Here's a eukaryotic cell.

Eukaryote means nucleus, eukaryote, a true nucleus.

DNA packaged up in here in chromosomes.

All these interesting organelles,

mitochondria, Golgi bodies, endoplasmic reticula.

We're not going to talk about lots of it,

although we'll make brief passing mentions of some of it.

But I hope you're all going to want

to learn about cell biology.

So all right, that's what we're not going to do in the course.

I'm mentioning them, because they'll come up.

You do need to know what a cell is.

Sometimes people think, where are these reactions we're

going to talk about going on?

Where's the DNA?

They're in there.

They're in the cell.

They're in the nucleus.

But you could spend a lot of time memorizing

lots of organelles, and it's not going

to be my intention that you memorize

lots of organelles in the cell.

It is important you know the difference between prokaryotes

and eukaryotes, proks and euks as we call them

amongst friends.

But that's about it.

So we'll put away our cell here.

Before we go on, we've got a few questions for you

on evolutionary time and cell size and scale.

For one of them, you're going to want to use this graphic here

that you'll find in the resource box.