Data reveals that long ago fish made the leap onto land

For many years scientists believed it was the development of limbs that led water dwelling creatures onto land. However, old fossil data may now reveal that it was in fact vision that prompted fish to make the leap onto land hundreds of millions of years ago. Malcolm MacIver, Professor of Mechanical Engineering and Biomedical Engineering at Northwestern University speaks with Hari Sreenivasan.


For many years, scientists believed it was the development of limbs that led water-dwelling creatures onto land.

However, old fossil data may now reveal that it was, in fact, vision that prompted fish to make the leap onto land hundreds of millions of years ago.

Here's the story.

Almost 400 million years ago, some adventurous fish made a huge leap that eventually led to the evolution of humankind.

They decided to come up on land.

We humans probably would never have evolved the intelligence we have today if not for that move onto land.


Because it vastly improved our eyesight.

According to neuroscientist Malcolm MacIver, the way we think about the world is closely tied to what we can see, and fish can't see a whole heck of a lot.

That's mainly because light doesn't travel very far in water.

Our ancient fish ancestors lived their lives in a constant fog, so their brains evolved to react quickly to whatever suddenly appeared on the horizon.

MacIver had a theory that the move to land expanded our aquatic ancestors' vision and, in turn, their brains.

To test his theory, he and paleontologist Lars Schmitz spent a year running simulations with fossil data.

Their research revealed new clues about why fish came onto land in the first place.

[ Fossil breaks ] It all seemed to have started when the first fish peeked above the water's surface.

Suddenly, it was able to see 70 times further.

And behold, a smorgasbord of tasty land-dwellers.

To capitalize on this discovery, the fish would have to evolve.

Its eyes soon moved to the top of its head and tripled in size, and its fins began evolving into limbs so that it could stalk its new prey like a crocodile.

Hunting on land was a mental game-changer for the early tetrapods.

Their total sensory volume increased a millionfold, giving them a much bigger window into the future.

The first animal that figured out how to plan accordingly, instead of just reacting, would have had a huge evolutionary advantage.

Iterate that kind of natural selection a million times, and eventually, we have something called prospective cognition.

That's our ability to weigh different options for the future and choose strategically.

To this day, fish have not evolved those kinds of complex planning skills, but many land animals have.

Understanding the evolutionary roots of intelligence helps explain how humans got so smart but also why we are so dumb.

We've evolved to deal with the things we can see in the here and now.

We still don't plan well for things that are too far away in time or space.

Will our vision ever evolve so that we can see the faraway consequences of our actions more clearly?

Evolution won't make that happen anytime soon, but understanding the relationship between vision and planning may help us engineer solutions like using technology to bring faraway things closer.

That just might give us the evolutionary advantage we need to survive the next 400 million years.

Here with us to discuss his research is Malcolm MacIver, professor of mechanical engineering and biomedical engineering at Northwestern University.

It's kind of an interesting idea when you looked at this fossil data.

I mean, this is something that we've thought about forever and ever.

We thought that fish grew limbs.

And they're... What's the vision connection?

Yeah, so the vision connection is that, well, 10 years ago, I predicted that animals coming up onto land, given that air was much more transparent, that would favor bigger eyes because air allows vision to work much better.

So myself and Lars Schmitz and some collaborators went and checked the fossil record, and what we found was actually much more interesting, which is that there was a tripling of the sockets that hold eyes just before we came up onto land.

So the idea is that this might have actually had something to do with coming up onto land.

So, how do I know which came first -- the eye sockets or the limbs or the -- You know what I mean?

Right. Yeah.

So, one thing is that it's clear that this tripling occurred before limbs became digited, before fingers and toes emerged.

So, up to that time, you can imagine a pectoral fin of a fish, kind of stubby, limblike thing, and they presumably paddled up onto land to get what they were interested in there, using those limbs.

So, there is this transitional period where you go from a finlike thing to a limblike thing.

The eyes triple in size, and then we see complete limbs in the record.

And there's also a correlation between our ability to see and how our brains develop.

Yeah, well, so, this is -- Sort of the origin of the idea was with this idea that animals in water, because they can only see about a body length in front of them, have to react to sensory input reflexively, kind of like what happens when somebody taps your knee, that they have to take sensory input indicating a looming predator or a prey, and they have to immediately react.

There's no advantage to strategic thinking in that kind of environment.

Now, once you're on land, you can see 100 times further out.

So now you could still react reflexively to what you see, but the first animal that can acquire the set of mutations that lets you sort of disconnect sensory input from motor output and think of possible futures and then pick the best one, that animal will have a massive evolutionary advantage.

What is this idea of this connection between how we think, our environment -- What does that mean for human evolution, going forward?

Right. So, you know, this is a really good question.

And what we think, studying this process or studying this possible evolutionary trajectory whereby we became analyzers of strategic futures, might help us see why we have certain holes in our ability to think strategically.

And in particular, a lot of people have noted that we have a very hard time thinking on geological time scales.

Thinking even three or four generations forward is very tough for people.

And one of the ideas we've suggested in our work is that this might trace back to why it is we became cognizant of multiple futures in the first place, which was to act very strategically in a fairly short range, like, for immediate benefit.

And we can bootstrap that with language and with, you know, plans over 5 to 10 years, but ultimately, what we're pointing to is it might be a difficult fit, and we might need to think very carefully about how we might augment our ability to think strategically to deal with problems like climate change and other things that happen over vast time scales.

So, how would we augment that?

Well, one of the things that is -- One of the things we could do is to think about, 'How do we make the distant consequences of our action, either spacially distant, as in affecting someplace else on Earth, or temporally distant, far away in the future -- How do we make those -- How do we put those into our sensory bubble?'

When you think about something like a nest or you think about a Prius car with those indicators showing what you're doing, what are the environmental or energetic consequences of what you're doing right now, if we can take long-range consequences of our behaviors, of our policies, and put those in and sort of draw back the conclusions of that into our current space, that may help us think more strategically at the current time.

Malcolm MacIver of Northwestern University, thanks for joining us.

Thank you.