The Man Who Counted Peas for Eight Years

Your child listens; you read. This page is here so you can answer the questions that come after the story. The script itself is available from the script button while the audio plays.

What this episode covers

A friar planted and counted peas in a monastery garden — for eight years, tens of thousands of them. From those numbers alone he worked out what parents pass on to their children. He had never seen a gene, and the word did not yet exist.

The story has two hearts. One is the moment when something that seemed to have vanished skips a generation and comes back. The other is that nobody recognised his work while he was alive. Thirty-four years later, three scientists each found the same rule, searched the old literature, and discovered his name.

What actually happened

• Gregor Johann Mendel (1822–1884), a friar at the Abbey of St Thomas in Brno, in what is now the Czech Republic. He had studied physics and mathematics at university, and that training turned out to matter.

• From 1856, for about eight years, he grew peas in the monastery garden. He followed seven traits — seed shape (round or wrinkled), seed colour, flower colour, pod shape and colour, flower position, and stem height.

• The accepted view at the time was blending inheritance: parental traits mix like paint, giving something in between.

• Crossing tall plants with short ones, every offspring was tall. There were no middling plants.

• Crossing those offspring with each other, short plants reappeared in about one quarter of the next generation. Nothing had been lost; it had been hidden.

• He presented his results in 1865 and published "Experiments on Plant Hybrids" in 1866. It drew almost no attention.

• In 1868 he became abbot; administration crowded out research. He died in 1884.

• Around 1900, three researchers working separately (de Vries, Correns, Tschermak) arrived at similar rules, and found Mendel's paper while searching earlier work. Genetics began.

• Worth knowing: the word "gene" was coined in 1909. Mendel never used it.

• He did not only count peas. An Augustinian priest at the Monastery of St Thomas in Brno, he was also a teacher of natural history and physics at the Brünn Modern School, made daily meteorological and astronomical observations, and cared for the monastery's fruit orchard and beehives and the greenhouse plants. The pea experiments ran 1856-1863, alongside all of that (PMID 35858394).

• He failed his exams. He failed his tryout as a parish priest and never completed his teaching certification despite two years at the University of Vienna (PMID 35858394).

• His last years were hard. Elected abbot in 1868, he badly underestimated the administrative load and gradually had to abandon his science; the final decade was marred by a bitter dispute with the civil authorities over monastery taxation (PMID 35858394).

• Today's genetics starts here. Modern genetics began with the rediscovery of Mendel's laws in 1900 (PMID 39586628), leading to chromosomes and the double-helix structure of DNA (PMID 41151784).

Questions your child may ask

"Why peas, of all things?" Because he chose well. Peas self-pollinate, so parentage can be controlled. Their traits fall cleanly into two categories — round or wrinkled, with nothing in between. They produce several generations quickly, and they are easy to grow. Choosing the right material is itself a skill, and this is a good place to say so.

"Do I look like Mum or Dad?" Here you need to draw a clear line. Human height, faces and temperament are nothing like peas. Many genes act together, and environment matters too. Mendel's rules tell us that what is inherited passes along in separate pieces rather than blending away — not that every human trait splits three to one.

"Why did nobody notice?" He was too far ahead. And what he did was explain biology with numbers, which was unfamiliar to biologists of his time. The journal he published in was also not widely read.

"Was he sad about it?" We do not know. He left no record of how he felt. What we do know is that he kept writing it down — which is why someone could find it thirty-four years later.

"Where was the hidden thing hiding?" We now call it a gene, and we know it is written in DNA inside cells. Mendel knew none of that. He reasoned his way to something he could not see, using nothing but counts. That is the astonishing part.

Ideas inside the story

• Dominant and recessive — why a trait can skip a generation and return.
• Particulate versus blending inheritance — passed on in pieces, not mixed away.
• The power of counting — turn observation into numbers and hidden rules appear.

What is evidence, and what is received story

Well-established The monastery garden experiments, roughly eight years, seven traits, a uniform first generation followed by about three to one, the 1866 paper, the lack of recognition in his lifetime, and the rediscovery around 1900.

Genuinely disputed In 1936 the statistician Ronald Fisher pointed out that Mendel's reported numbers fit the theory suspiciously well, and the argument continues today. Explanations range from deliberate adjustment to the conventions of the period to unconscious selection. There is no settled answer. It is not in the children's story, but it is excellent material for a later conversation about how even great scientists are subject to scrutiny.

Deliberately left out Anecdotes about whether Mendel did or did not read Darwin. Not firmly established, so not included.

Sources and what followed

Original paper — Gregor Mendel, Versuche über Pflanzen-Hybriden (Experiments on Plant Hybrids), 1866. Listed in Paperis' Shoulders of Giants under basic science.

What this discovery led to

• The birth of genetics — after 1900, inheritance became a field of its own.
• The road to DNA — what is passed on (Mendel) → what it is made of → what shape it takes. Several entries in Shoulders of Giants sit along that sequence.
• Medicine today — how inherited conditions work, genetic testing, and gene editing all descend from this line.

Try this together

• Spread out family photographs and look for a resemblance that skipped a generation — something a grandparent has that the parents do not. It maps exactly onto the story.
• Plant a few beans or peas in cups. Sprouts appear within days, and with several plants you can see that they do not all come out the same.
• Count something twenty times and write it down — how often you catch a red light, for instance. It is the cheapest way to feel how counting reveals a pattern.