History

10 Major Scientific Discoveries That Changed Humanity

From penicillin to DNA, from the printing press to germ theory: ten scientific breakthroughs, the context that produced them, and the often-forgotten people behind them.

By Updated on 9 min read

The history of science is usually told through a handful of iconic figures: Newton and his apple, Einstein and his relativity, Galileo and his telescope. But hundreds of other breakthroughs have changed daily life, medicine, food and communication far more radically than any of those famous stories suggest. A petri dish left on a London windowsill. A flash of insight in a Pisa cathedral. A fragment of glowing matter in a Paris laboratory. Science often advances through accidents caught in time by attentive minds.

This article walks through ten discoveries that reshaped humanity, chosen for their concrete impact and for the personal stories behind them. You will meet an English country doctor inoculating children with cowpox pus, an American dentist putting his patient to sleep with ether, a French chemist guillotined during the Revolution, and a British crystallographer whose photograph cracked the structure of life itself.

1. The movable-type printing press: Gutenberg, around 1450

Before Johannes Gutenberg, copying a book took months and cost a fortune. Medieval manuscripts were reproduced by hand in monastic scriptoria, which kept books in the hands of a clerical and aristocratic elite. In Mainz, around 1450, Gutenberg assembled a system based on three innovations: metal movable type in a lead-antimony-tin alloy, an oil-based ink that clung to metal, and a press adapted from the wine presses of the Rhineland.

His 42-line Bible, printed around 1455 in roughly 180 copies (forty-nine of which survive today), proved the method was viable. Within fifty years, presses had spread across Europe. Scholars estimate that about 20 million books were printed before 1500: these incunabula outnumbered every manuscript copied in the previous thousand years combined. The Protestant Reformation, the Enlightenment, the scientific revolution of the seventeenth century: none of it is conceivable without the mass diffusion Gutenberg made possible. He himself died ruined in 1468, after losing his workshop to a lawsuit brought by his financial backer.

2. Vaccination: Edward Jenner, 1796

At the end of the eighteenth century, smallpox killed around 400,000 Europeans every year and disfigured millions more. Edward Jenner, a country doctor in Gloucestershire, noticed that milkmaids who had caught cowpox (a mild bovine disease) never came down with human smallpox. On May 14, 1796, he scraped pus from the hand of a milkmaid named Sarah Nelmes and inoculated an eight-year-old boy named James Phipps. Six weeks later, Jenner exposed the child to live smallpox. The boy did not fall ill.

The word vaccination comes directly from the Latin vacca (cow). Jenner published his results in 1798. The method spread worldwide and made it possible, in 1980, for the WHO to declare smallpox eradicated: the first and so far the only human disease completely wiped out by medicine. Smallpox had killed more than 300 million people in the twentieth century alone before the global vaccination campaign finished it off.

3. Oxygen and modern chemistry: Lavoisier, 1778

Before Antoine Lavoisier, chemistry was still ruled by phlogiston theory: people believed substances burned by releasing a hypothetical fluid. Lavoisier, a tax farmer and dedicated chemist, used precise measurements to show that combustion is actually a combination with a gas, which he named oxygen (Greek for "acid-maker," a partly mistaken etymology that stuck). He stated the law of conservation of mass: nothing is lost, nothing is created, everything is transformed.

Together with his wife Marie-Anne, who translated English sources and illustrated his treatises, Lavoisier published the Traité élémentaire de chimie in 1789, the founding text of modern chemistry. He was guillotined on May 8, 1794, at age fifty, a victim of the Terror. The mathematician Lagrange remarked the next day: "It took only a moment to cut off that head, and a hundred years may not be enough to produce another like it."

4. Surgical anesthesia: Crawford Long, 1842

For thousands of years, surgery was performed on fully conscious patients, held down by force, screaming through the procedure. A handful of opium- or alcohol-based mixtures barely dulled the pain. On March 30, 1842, in Jefferson, Georgia, the physician Crawford Williamson Long removed a tumor from the neck of a patient named James Venable, who was rendered unconscious with diethyl ether. The patient felt no pain. He paid $2.25 for the operation.

Long, working far from the medical journals of the time, delayed publishing his results. The dentist William T. G. Morton gave a public demonstration of ether anesthesia at Massachusetts General Hospital in Boston in 1846: the event most often cited as the official birth of anesthesia. Morton tried to patent the procedure under the trade name letheon, without success. Anesthesia opened the door to abdominal, neurological and cardiac surgery: essentially all of modern medicine flows from it.

5. Germ theory: Louis Pasteur, 1860-1880

In the mid-nineteenth century, disease was still widely blamed on miasmas, foul vapors rising from swamps and garbage. Louis Pasteur, a trained chemist, used a series of experiments to show that fermentation and putrefaction are caused by living micro-organisms. His swan-neck flask experiment in 1859 proved that a sterilized broth stays sterile as long as airborne particles cannot reach it. Spontaneous generation was finally laid to rest.

Pasteur applied his theory to industry (rescuing French wine, beer and silk production) and to medicine. On July 6, 1885, he inoculated nine-year-old Joseph Meister, bitten by a rabid dog, with the first rabies vaccine. The child survived. Pasteurization, the gentle-heating process he developed for wine and which was later applied at scale to milk, has probably saved more lives than any single vaccine ever did.

6. Atomic structure: Rutherford and Bohr, 1911-1913

In 1911, Ernest Rutherford, in his Manchester laboratory, bombarded a thin gold foil with alpha particles. To his astonishment, a tiny fraction of those particles bounced straight back, as if a shell had been fired at tissue paper and returned to the sender. The conclusion: the atom is almost entirely empty space, with a dense, positively charged nucleus at its center.

Two years later, the Dane Niels Bohr proposed a model in which electrons orbit the nucleus at quantized energy levels. That model, still taught today in simplified form, opened the road to the quantum mechanics of Heisenberg, Schrödinger and Dirac. Without an understanding of atomic structure, nuclear energy would not exist. Neither would semiconductors, MRI scanners or lasers.

7. Penicillin: Alexander Fleming, 1928

On the morning of September 3, 1928, Alexander Fleming returned from a holiday to his lab at St Mary's Hospital in London. He had left a stack of petri dishes containing staphylococcus cultures sitting out before he left. One of them was contaminated by a green mold, Penicillium notatum, and around the mold a perfectly clear zone had formed where the bacteria had been killed.

Fleming published his findings in 1929, but the scientific community received them with little enthusiasm. It would take until 1940 for Howard Florey and Ernst Chain, at Oxford, to isolate penicillin in usable quantities. Industrial production, scaled up in the United States during the Second World War, saved tens of thousands of wounded soldiers. Fleming, Florey and Chain shared the Nobel Prize in Medicine in 1945. Penicillin and its derivatives are estimated to have saved more than 200 million lives since 1942.

8. The structure of DNA: Watson, Crick and Franklin, 1953

At the Cavendish Laboratory in Cambridge, James Watson and Francis Crick had been working since 1951 to crack the structure of deoxyribonucleic acid. The missing piece came from King's College London: Photo 51, an X-ray diffraction image taken by Rosalind Franklin in May 1952. Maurice Wilkins, Franklin's colleague, showed the photo to Watson without Franklin's consent. Watson saw the double helix immediately.

On April 25, 1953, Watson and Crick published a one-page article in Nature describing the DNA double helix with its two antiparallel strands and complementary base pairs (adenine-thymine, guanine-cytosine). Rosalind Franklin was not credited on the main paper. She died of ovarian cancer in 1958 at thirty-seven, four years before the Nobel Prize was awarded to Watson, Crick and Wilkins in 1962, and the Nobel cannot be awarded posthumously. The human genome was fully sequenced in 2003, a direct descendant of that one-page article. Personalized medicine and gene therapy are its grandchildren.

9. Radioactivity: Henri Becquerel and the Curies, 1896-1898

On March 1, 1896, Henri Becquerel discovered by accident that uranium salts exposed a photographic plate wrapped in black paper without any external light source. A new form of radiation existed, with no need for any outside trigger. Marie Curie, a young Polish woman living in Paris, chose the phenomenon as the subject of her doctoral thesis. Working with her husband Pierre, she isolated two unknown elements: polonium (named after her homeland) in July 1898, then radium in December.

To produce a tenth of a gram of pure radium chloride, the Curies processed several tons of pitchblende ore by hand in a leaky shed at the Paris School of Industrial Physics and Chemistry. Marie Curie won the Nobel Prize in Physics in 1903 and another in Chemistry in 1911: the only person ever to win Nobels in two different scientific disciplines. She died of aplastic anemia in 1934. Her laboratory notebooks remain so radioactive today that they have to be consulted under lead shielding.

10. Binary arithmetic and theoretical computing: Leibniz, 1703

In 1703, the German philosopher and mathematician Gottfried Wilhelm Leibniz published his Explication de l'arithmétique binaire, presenting a numeric system based only on the digits 0 and 1. Inspired by the Chinese I Ching and its hexagrams, Leibniz saw in this binary pair a philosophical image of creation: God (1) and the void (0).

It would take until 1854 for George Boole, in his Investigation of the Laws of Thought, to formalize the associated Boolean algebra. Then Claude Shannon, in his MIT master's thesis in 1937, showed that electrical circuits could physically embody that algebra. Every computer, every smartphone, every server that runs the internet today rests in the end on this 300-year-old insight. Without Leibniz, no programming. Without Boole, no logic gates. Without Shannon, no transistor.

What these ten stories have in common

A scientific discovery almost never arrives alone. It grows out of decades of earlier work, takes advantage of new technical capabilities (microscopy, analytical chemistry, crystallography) and sometimes depends on absurd accidents: a draft carrying spores into a lab, a photograph passed around without permission, a dish left out by carelessness. Researchers do not work alone either: behind every famous name stand dozens of assistants, technicians, spouses or colleagues that history has often erased.

Several lessons keep returning. Recognition often comes late, sometimes after death. Many discoveries move against the dominant theories of their time. And science, contrary to the myth of the lonely genius, advances through communities in constant argument.

If the history of science draws you in, you can test your knowledge with our history and science quizzes on SparkleQuiz and challenge your friends on the dates, names and odd anecdotes behind these great intellectual adventures.

Put your knowledge to the test

Ten discoveries, ten centuries of accidents caught in time: now see which dates, names and petri dishes your own memory has retained. These quizzes stay right in the territory of this article:

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