Colorblindness: John Dalton's Preserved Eye and Seeing Through Camouflage

SPEAKER_1 (0:00)

Back in 1995, there was this team of scientists huddled in a lab, and they were delicately extracting DNA from a human eyeball.

SPEAKER_2 (0:08)

Which is wild on its own, but the kicker is that this eyeball was 150 years old.

SPEAKER_1 (0:14)

Right. It had literally been floating in a preservative jar since, I think, 1844, and it belonged to the really famous 18th century English chemist, John Dalton.

SPEAKER_2 (0:25)

Yeah, and it is just a phenomenal piece of scientific history, because Dalton actually left explicit instructions that his eyes be preserved after his death.

SPEAKER_1 (0:34)

He wanted them to figure out his own mystery, right?

SPEAKER_2 (0:36)

Exactly. He had this very specific unsolved mystery he wanted future generations to figure out. He knew his vision was vastly different from all the people around him.

SPEAKER_1 (0:47)

He had a whole hypothesis about it too. He believed the fluid inside his eye, like the vitreous humor, was physically tinted blue.

SPEAKER_2 (0:54)

Right, like a built-in filter.

SPEAKER_1 (0:56)

Yeah. He thought it was acting like a colored filter, just absorbing red and green light before it could even reach his retina.

SPEAKER_2 (1:02)

Which is a perfectly rational guess for the 1790s. I mean, without modern tools, what else would you think?

SPEAKER_1 (1:08)

Makes total sense.

SPEAKER_2 (1:09)

But when scientists finally ran the genetic analysis on his preserved retina a century and a half later, they proved the blue fluid theory completely wrong.

SPEAKER_1 (1:20)

But they did figure it out?

SPEAKER_2 (1:21)

They did. The DNA analysis definitively identified the genetic variation that caused his unique perception of the world. He was basically just missing a crucial piece of biological hardware.

SPEAKER_1 (1:33)

Which brings us to what we are getting into today. Because we built modern society on this massive assumption that everyone sees the exact same red and green.

Today we are looking at what happens when human biology proves that assumption completely wrong. We are stepping into the incredibly fascinating world of color vision deficiency or CVD.

SPEAKER_2 (1:53)

Though I should mention the term deficiency is heavily debated as we'll explore.

SPEAKER_1 (1:59)

Oh really?

SPEAKER_2 (1:59)

Yeah, because normal is a highly subjective baseline when you really examine the mechanics of human perception.

SPEAKER_1 (2:06)

That is a great point.

And if you are looking at your smartphone screen right now, every color you see is basically a biological trick. So whether you have standard color vision or you suspect you might be part of the roughly 8% of men or 0.5% of women with red-green color blindness, this deep dive is for you.

SPEAKER_2 (2:24)

We're going to cover a lot of ground today.

SPEAKER_1 (2:26)

Definitely. We are going to unpack the genetics, the surprisingly cool evolutionary advantages of seeing through camouflage, and how our modern world kind of penalizes a simple genetic variation.

SPEAKER_2 (2:38)

So to really understand what was actually happening inside John Dalton's eyes, and in the eyes of millions of people today, we first have to map out the biological machinery of color vision.

SPEAKER_1 (2:49)

Okay, let's unpack this, because we have to dispel a major myth right out of the gate.

SPEAKER_2 (2:53)

No, the black and white TV myth.

SPEAKER_1 (2:55)

Exactly. When people hear the phrase color blindness, they almost always imagine 1950s black and white television, like just a complete gray scale world.

SPEAKER_2 (3:05)

Right. And that condition does exist.

SPEAKER_1 (3:07)

But it's called monochromacy.

SPEAKER_2 (3:09)

It's super rare.

SPEAKER_1 (3:10)

But it's super rare, right?

SPEAKER_2 (3:12)

Exceedingly rare. True monochromats truly do not perceive hue. But for the vast majority of people with a color vision deficiency, they see plenty of vivid color.

SPEAKER_1 (3:21)

It's just different.

SPEAKER_2 (3:22)

Exactly. The mechanical difference lies specifically in the cone cells at the back of the retina.

SPEAKER_1 (3:27)

So you have three classes of these cone cells, and they're detecting light at different wavelengths. You've got L cones for long wavelengths, which peak in the reds. You have M cones for medium wavelengths, peaking in the greens.

And then S cones for short wavelengths, peaking up the blues.

SPEAKER_2 (3:43)

Right. And most color vision variations occur when one or more of these cone types either doesn't function, is completely missing, or is genetically mutated, so its sensitivity shifts along the spectrum.

SPEAKER_1 (3:55)

Okay, let's focus on the two main categories here. First, there's dichromacy, where you are just entirely missing one of those three cone types.

SPEAKER_2 (4:03)

Just gone completely.

SPEAKER_1 (4:04)

Right. And second, you have anomalous trichromacy. In that case, you have all three cones, but one of them is essentially mutated and detects a slightly different wavelength than it was originally designed to.