Podcast Summary: Stuff You Missed in History Class – SYMHC Classics: John Dalton

Hosts: Holly Frey & Tracy V. Wilson
Original Air Date: January 20, 2021 (Classic episode rebroadcast on September 6, 2025)
Main Topic: The life and work of John Dalton, with a special focus on his pioneering study of color vision deficiency ("Daltonism")

Episode Overview

This episode dives into the scientific legacy of John Dalton, known for his atomic theory and foundational work in chemistry and meteorology, but here primarily celebrated for his groundbreaking insights into color vision deficiency. Holly and Tracy use Dalton’s life to explore the evolution of scientific understanding about color perception, genetics of color vision anomalies, and Dalton’s exceptionally detailed, humorous, and intuitive self-experimentation.

Key Discussion Points & Insights

The Universal Question of Color Perception

• Both hosts reminisce on childhood questions about whether others see colors the same way.
• Tracy shares a personal anecdote: “I asked the same question of my father...he did not see color the way the rest of grief did...” (04:23)
• This curiosity ties directly to Dalton’s own journey: Dalton did not initially realize he perceived colors differently until well into adulthood.

Scientific Terminology and Genetics of Color Vision Deficiency

• The hosts explain why the term "colorblindness" is falling out of favor, replaced with "color vision deficiency" for clarity (06:48).
• Tracy details prevalence based on a 2014 study, highlighting its X-chromosome linkage and higher frequency in boys, especially white boys (10:15).
• Genetics breakdown: Red-green CVD is X-linked (so more common in males), blue-yellow is autosomal dominant and not sex-linked (11:21).

Historical Context and Dalton’s Place in Science

• The phenomenon of color vision deficiency was noted before Dalton but never rigorously studied.
• Dalton’s 1794 paper, “Extraordinary Facts Relating to the Vision of Colors,” is recognized as the first systematic analysis. Tracy sets up context: “The first systematic analysis appears in 1793...and that brings us to John Dalton.” (13:11)

John Dalton’s Early Life and Career Trajectory

• Born September 5 or 6, 1766, to a Quaker family (13:11).
• Began teaching by age 12, eventually teaching at New College in Manchester, then becoming a private tutor to focus on scientific research (14:28).
• Initial scientific pursuits included meteorology; later, a key discovery in color vision arrived from botany studies (15:04).

Dalton's Pioneering Self-Study of Color Vision

The Discovery

• Trigger moment: Observing geraniums by candlelight; flowers perceived as blue in daylight turned red in candlelight, revealing the difference in his vision compared to others (22:12, 22:52).
• Dalton's brother shared these perceptions, leading to their investigations.

The Experiments

• Used a prism to separate light, asked participants how many colors they saw. Most saw six, Dalton only two or three (23:42).
  • Notable Quote (Dalton):

    "That part of the image which others call red appears to me little more than a shade or a defect of light." (24:33)

• Detailed, often amusing descriptions of his perceptions:
  • Crimson: “Crimson has a grave appearance, being the reverse of every showy and splendid color.” (25:06)
  • Blood: Appeared “bottle green” to him; couldn’t distinguish it from dirt stains.
• Explored responses from other people with similar vision, including the Harris family, concluding the trait was familial and more common in males (28:09-29:24).

Early Contributions to Genetics

• Appearances of CVD in male family members but not females led Dalton to suspect sex-based inheritance, foreshadowing later genetic discoveries (29:24-30:06).

Dalton's Theories about the Source of CVD

• Hypothesized a colored “humor” (fluid) in the eye filtered out certain color wavelengths, based on how things looked when seen through stained liquids (34:17).
• Tracy: “He came to this incorrect conclusion...that one of the humors of my eye must be a transparent but colored medium...” (34:17)
• Left instructions for his eyes to be dissected posthumously to test this theory (35:59).

Posthumous Science & Legacy

Dalton’s Death and Aftermath

• Dalton died July 27, 1844; public funeral drew 40,000 mourners (40:15).
• His eyes were dissected and preserved—no colored humor was found; tissues were perfectly clear (40:38).

Modern Analysis

• Centuries later, DNA analysis of Dalton’s eyes confirmed a diagnosis of deuteranopia (red-green color vision deficiency) (41:13).
• Dalton's preserved eyes remain on display at the Science and Industry Museum, Manchester (41:51).

Developments Beyond Dalton

• Thomas Young’s theory (1801): Three receptors for red, green, blue—essentially correct, but took decades more for the science to advance (36:35).
• 19th and 20th century advances: Identification of rods/cones, understanding of retina structure, and most recently, discovery of ganglion cells as a third photoreceptor type (42:02).

Notable Quotes & Memorable Moments

• On Terminology:

  • Holly: “Colorblindness is a term that's falling out of favor because it's not really accurate. Colorblind suggests that somebody can't see color at all.” (06:48)

• Dalton, describing red:

  • “That part of the image which others call red appears to me little more than a shade or a defect of light.” (24:33)

• On observing differences in candlelight:

  • “This significant shift in their color due to lighting changes startled him and led him to make a quick study by asking a number of friends to look at these same flowers...” (22:12)

• On CVD inheritance:

  • “It is remarkable that I have not heard of one female subject to this peculiarity.” (29:24)

• On scientific speculation:

  • Tracy: “He came to this incorrect conclusion...that one of the humors of my eye must be a transparent but colored medium...” (34:17)

• Dalton’s legacy:

  • Tracy: “He is also sometimes called the father of chemistry.” (38:28)

Important Timestamps

| Timestamp | Segment | |-----------|----------------------------------------------------------| | 02:40 | Episode theme intro: John Dalton and color vision | | 06:48 | Discussion on terminology: “colorblindness” vs. “CVD” | | 10:15 | 2014 study: Prevalence and genetics of CVD | | 13:11 | Dalton’s birth and early life | | 15:26 | Dalton’s early work in meteorology and science | | 22:12 | Dalton’s pivotal flower observation by candlelight | | 23:42 | Prism experiments—how Dalton perceived colors differently| | 24:33 | Dalton’s own descriptions (notable quote) | | 29:24 | Family studies and early insights into inheritance | | 34:17 | Dalton’s colored humor hypothesis and self-experiment | | 40:15 | Dalton’s death, posthumous dissection, and public honors| | 41:13 | DNA analysis confirming Dalton’s diagnosis | | 42:02 | Advances in vision science beyond Dalton |

Final Thoughts

This episode balances Dalton’s chemistry legacy with his remarkable foray into self-observation, systematic study, and speculation about color vision. Holly and Tracy’s conversation combines scientific curiosity, personal anecdotes, and historical context, making Dalton’s story vivid, relatable, and informative for a contemporary audience.

For listeners new to John Dalton, this episode offers not only a window into early color vision studies but also a model of how individual curiosity can lead to lasting scientific legacies.