Thanks to Brilliant for  supporting this SciShow video!

Because you watch SciShow, Brilliant  is offering the first 200 people who sign up a 30 day free  trial and 20% off an annual premium subscription at Brilliant.org/SciShow. Imagine if nobody had eyes.

I don’t mean people are born blind – I mean vision as a concept hasn’t  happened to our species yet. And then one day, all of the  sudden, out of nowhere, BAM. A kid is born who has eyes.

Who can see. So where did these whole  entire eyes suddenly come from? It can’t be a natural selection  thing, because there weren’t, like, sort-of-but-not-yet-eyes for it to act on.

There were no eyes and no vision, at all. And yet, there he is. The Kid With The Eyes.

And no, this isn’t the next  dystopian teen chosen one TV show. It’s a real question that’s given scientists headaches all the way back to Darwin. And now, we may finally have an answer, but one that causes even more headaches. [♪ INTRO] In order for evolution to act,  it needs something to act on.

Natural selection acts on what’s already there, so a fin becomes a leg and later a wing. That means the evolution of something totally new and innovative is pretty rare. And there are two competing  ideas about how it happens.

One is that these traits develop gradually, in tiny little increments  over long periods of time. The other is that they’re caused  by sudden, massive changes, like a major mutation, that gives  an organism a major advantage. So, let’s use our eye example  to take a look at this.

A working eye that allows us  to see and interpret the world involves a lot of parts evolving  and working together in tandem. Eyes don’t just detect light. Human  eyes detect color and distance, and have muscles to focus and  shift their field of view.

In the gradual version, you’d  expect those to show up slowly and one at a time. But there’s  actually a bit of a problem. Some of the little changes required to make the final eye work might not  be immediately beneficial – and that means natural selection probably won’t do anything with them one way or the other.

The other option is that  there were one or more big, sudden mutations that resulted  in immediate huge changes. Changes that were massively  beneficial and so massively favored, that all of a sudden, an eye  sprung into existence fully formed. In this version, evolution of  these traits looks like giant leaps followed by calm periods, as  opposed to a steady progress.

But this also seems kind  of unlikely, because, well, how did a sudden mutation come  up with a whole working eye? Scientists have wondered about how these so-called key innovations develop for more than a century. And in January 2024, two papers  published in the journal Science might have finally given us the  tools to solve that mystery.

The first study looked at carnivorous  plants called pitcher plants, some species of which have a pretty  diabolical method for trapping prey. If an ant is chilling on the  lid of a pitcher plant leaf when the plant gets hit with  a drop of water, that drop turns the lid into a catapult  that launches the ant directly into cup-shaped leaves that  trap the ants in a pool of fluid. In order for this to work, three  different traits had to evolve.

One is the lid that catapults  the insects into the leaf-cup. The second is a just-right slippery  texture that allows ants to hang onto the lid generally, but  be dislodged when water hits. And then there’s the springboard  catapulting mechanism itself.

Importantly, none of these traits are enough to catch an ant on their own, or even in pairs. It takes all three of them to make dinner happen. So it would make sense that all three of these traits co-evolved to work together.

But according to an international research team, that’s not what happened. Instead, it appears that each  of the three traits developed mostly or completely  independently from the other two. Basically, before this innovation, these species of pitcher plants had a ton of  variation in different traits.

Some might have had horizontal lids,  some were slipperier than others, and some had lids that springboarded. In fact, that’s exactly the  case with some related species. When the researchers compared  between these other species, they didn’t find correlations  between the three traits.

They also found that in species  without springboard trapping, these traits looked very different than  they do in our flinging flora friends. You’d expect that if traits were actively evolving toward springboard trapping,  they’d be getting closer and closer to what we need for catapulting. So, for example, even in species  that didn’t springboard or have completely horizontal lids,  their lids would be close to flat.

But they’re not. Taken together, these findings  suggest that at some point, all three of these traits just happened  to appear together at the same time, and only after that did they maybe start evolving together driven by natural selection. So basically, a plant appeared  that just randomly happened to have all of the parts needed  for springboard trapping.

The innovation happened when  those parts came together, but it was already in the works. And what’s really wild is that this happened in two different species of pitcher plants. The two species are separated by  over 4000 kilometers of ocean, and the species that are  evolutionarily in between them don’t use springboard trapping.

If I had a nickel for every time pitcher  plants evolved a springboard trap, I’d have ten cents, which isn’t much  but it’s weird that it happened twice. Around the same time as the  carnivorous pitcher plant study, a separate group of researchers in  Europe were studying a different trait, this one in an animal. Most snails lay eggs, but one species of marine snails give birth to live snail babies.

The research team looked at the  genomes of the live-birthers and their closest relatives,  hoping to find the parts of the genome that coded for live birth. And they found that there  were several different gene locations associated with  the method of giving birth. They also found that those locations didn’t change at the same rate as the rest of the genome.

Which tends to be a sign that natural  selection is keeping them that way. The research suggests that the  all of the genes associated with birthing live babies came together  slowly over about 100,000 years. It’s unclear at what point in that process the reproductive method actually switched over, but the genetic evolution has  been in the works for a long time.

And just like pitcher plant springboard trapping, this may have evolved in snails more than once! If I had a nickel for every time  in this video a key innovation occurred multiple times independently…  well, I’d also have ten cents. And if I had a nickel for every  time this script called for an “If I had a nickel” joke, I’d also  have ten cents.

Or, fifteen, I guess. So here are two cases where a fundamental, species-altering complex  trait didn’t suddenly appear due to a big genetic mutation. Instead, the pitcher plants  had traits that gradually evolved separately and then got really lucky to come together in the right way.

And in the snails, the necessary  versions of the right genes for live birth were slowly collecting over time. And natural selection was doing  that, though we don’t know exactly what those genes do  so we can’t say exactly why. Plus, this appears to have happened more than once in both of those species.

So as far as arguments go, it’s  gradualism 2, big evolutionary leaps 0. Neither study finds a single giant leap, and both show how the new innovation had the groundwork laid for it ahead of time. Now while most of us don’t catapult insects into slippery cups on the regular, humans do have an incredible  number of these types of traits, so learning more about them  in other species might give us some insight on how we came to be  able to do all the things that we do.

But we still don’t know how these  genes got selected for or exactly what kind of genetic changes happened  that resulted in the new traits. Because if the genes hadn’t  manifested as traits that were any different from others, what was  natural selection even acting on? How did natural selection favor the genes that The Kid With The Eyes got  if there weren’t any eyes?

Hopefully these answers,  like eyes, will come in time. But in the meantime, you can  wonder what other new traits may be collecting just under the surface. This SciShow video is supported by Brilliant: the interactive online learning platform with thousands of lessons in science,  computer science, and math.

And sure, you can’t build your own body, putting eyes all over the place willy-nilly. But you can build code to accomplish  different kinds of complex tasks. And Brilliant has a course to help you do that.

It’s called Thinking in Code and  it’ll have you problem solving like a programmer in just 11 lessons. You’ll learn about loops, conditional statements, variables, and all that programming stuff. And when you finish up with the basics, Brilliant has more courses to take  your coding skills to the next level.

So to get started, go to Brilliant.org/SciShow or the link in the description down below. That link also gives the  first 200 people who sign up 20% off an annual premium Brilliant subscription. And you’ll get your first 30 days for free!

Thanks for watching this SciShow video! [♪ OUTRO]