Today on It's Okay to be Smart, thumbs the word!
[Intro] The ancient Greeks called it the second hand.
It could kill a gladiator or even set off a Shakespearean tragedy.
It could build a tool or even... hold on a sec.
Now it's hard to put a finger on the best evolutionary adaptation, but thumbs are up
there.
And we're not the only animals with opposable digits, but it's hard to imagine being human
without these little guys.
So what can a little blue hedgehog and an ancient fish teach us about how these guys
evolved?
To find out, I hitched a ride to chat with paleontologist Neil Shubin.
Alright I'm here with a really special friend today, Dr. Neil Shubin.
N: Great to be here, thank you.
J: So you work in a medical school.
Why does a medical school need a fish paleontologist?
N: The reality is often some of the best road maps to our own bodies lie in other creatures.
An entire branch of the tree of life is embedded in every cell, every gene, every organ of
your body.
And our challenge as anatomists, as geneticists, is to untangle that history.
Neil studies both the past and the present.
By looking at modern genes, he can study how living chemistry molds all those "endless
forms most beautiful" that Darwin talked about.
And by digging up ancient fossils, he can see how our bodies have changed over time.
And one of those fossils in particular has completely redefined our journey out of the
water.
N: Okay, so this is a cast of a skull from a creature that's 375 million years old.
And it's from the arctic, about 600 miles from the North poles.
It's a fish, but it's a special kind of fish.
It's called tiktaalik.
It has a paired set of nostrils in the front.
This is a fish that, if I were to show you it's body, clearly has scales on its back.
And fins with fin webbing.
But if you look inside the fins you find elements that correspond to your upper arm, forearm,
even parts of your wrist, inside this fish.
Tiktaalik is one of the most amazing fossil finds of all time.
It's a so called transitional form.
It's a fish with legs.
That helps us connect the dots on the evolutionary tree between fish that swim and animals that
walk.
By studying those ancient bones, we discovered that the arms that carried that fish out of
the water aren't that different from these.
N: Here's the beautiful thing.
Take your arm.
Okay.
You have bone inside here.
You have one bone here, two bones here, lot's of little bones in through here, and then
your fingers right?
When we look at the fossil record, what we can see is the assembly of this one bone,
two bone, little bone, finger pattern.
What tiktaalik has...
It's a fish.
With a fin.
But if you were to shed out those fin rays and take off the scales, what you would see
are versions of your upper arm, elbow, forearm, and wrist in this fish.
And then we can trace that all the way up from the fish to land-living animals, and
we can trace it even back further down from tiktaalik to fish.
That's what we do as evolutionary biologists, look at the assembly of this beautiful organ
here.
J: Wow, so...
Look at this arm guys.
This is 375 million years in the making.
So what does any of this have to do with making thumbs?
Well, to get this, you need this.
And to get any of this, you have to be born.
Now all of us started as one cell from a sperm and an egg.
And that became the trillions more that make our bodies.
N: Think about it.
This begins as a little bud.
Four little buds.
Beep beep boop boop.
Four little buds pop out of your body as little embryo.
And those buds, they push out of the body, filling with cells inside.
And that bud begins to form a paddle.
And that paddle is where the hand will appear.
So as this paddle appears, cells are dividing inside there.
And genes are being turned on and off.
And it's the activity of those genes being turned on and off that sort of orchestrates
the process of the formation of the different fingers in your hand.
Okay Neil.
It's one thing to make an arm, a hand, or even fingers.
Even a frog could do that.
Kermit: Okay, and I also have a hand at the end of this arm over here.
See that?
Yeah.
But that doesn't explain my thumb.
Why does it look different from my pinky?
[Surf music]
N: One of the reasons is because the genes are being turned on and off in different parts
of your developing hand in different ways.
One patch of tissue, right at this corner, right under where the pinky will form, is
really important.
Because, a signal is produced, in that little patch of tissue, that migrates across the
developing finger bud.
And the cells respond to that signal to develop different fingers in different ways.
J: What's that guy called?
N: Sonic hedgehog, after the video game.
J: After the video game.
The fact that I can play video games, hold my controller, is due to...
N: Sonic the hedgehog.
J: Sonic the hedgehog...
That's really cool.
Sonic: Triple cool.
Express too much Sonic hedgehog in the embryo and you get extra fingers.
Too little and your digits go from five to four.
Wait a sec...
I think I just figured out how the Simpsons evolved.
John Saunders discovered that if you transplant a tiny patch of that tissue on the opposite
side of the bud, you create a mirror image wing in chickens.
And we don't just find Sonic hedgehog in humans.
We find it in fish, and frogs, and chickens, and mice, and probably even real hedgehogs.
And it does similar things in those animals as it does in humans.
Of course, genes like Sonic hedgehog play in harmony with many other genes.
It's just one instrument in that beautiful orchestra of chemical signals.
The search for inner fish and inner hedgehogs is a story of how genes and fossils, two different
branches of science, come together to form the tree of life.
J: Thank you so much for joining me today.
I've learned a lot about my inner fish, and I hope that you have too.
If you want to learn more, check out Neil's book Your Inner Fish.
It is awesome, there's so many great stories.
You really feel like you're in the field with him.
And PBS has a special three part series premiering Wednesday April 9th at 10pm Eastern, also
called Your Inner Fish.
What do we say Neil?
N: Stay curious.
J: It's my inner fish.
Who's got two thumbs and wants you to subscribe?
This fishy guy.
Also check out the info below where you can watch Neil's new series, Your Inner Fish,
premiering on PBS this week.
And check out the link down in the description, his book by the same name.
[preview] My 165 millionth great grandparent is not
even a mammal.
It's a prehistoric lizard that predates even the dinosaurs.
They've got their own photo album, their own stack, that joins up with ours somewhere around
here.
In fact, every species has their own stack that branches off somewhere down the line.