Charles Darwin was distraught. Here he was, that famed white-bearded scientist, reading a letter from his young mentee. The letter had traveled across the globe, from Malaysia to Darwin’s home in England, where he was in the process of writing the book that would become his crowning glory. By that July day in 1858, Darwin was already a well-established scientist.

For two decades, he had been slowly writing On the Origin of the Species, the book that made Darwin one of the most famous scientists of the 19th century and a photo-worthy historical figure in every middle school science textbook. But the draft still wasn’t done. And on July 1, this letter arrived by steamboat from his young mentee, and it described a theory exactly like the one Darwin had been cooking up for two decades.

The letter was from a young scientist named Alfred Russel Wallace. The theory was natural selection. In case you forgot, natural selection is the now-proven theory that the organisms best adapted to their environments survive and produce more offspring with those same genotypes, while others die off. It is believed to be the most crucial step in the process of evolution — “survival of the fittest.” Scientists at the time knew that evolution was happening, but they still hadn’t figured out how. Darwin’s theory (and, apparently, Wallace’s) would radically shift the study of evolution and our understanding of the world around us.

Darwin began formulating his version of the theory in the late 1830s, according to his papers and correspondence. He worked on it quietly for 20 years, gathering data and building up as strong of a case as he could. He sent his work and theories to friends but did not write or read anything for public consumption. But during that time, he and Wallace corresponded, with Darwin acting as a kind of mentor, and Wallace sending Darwin species of birds from his studies in South America and Asia. Though they were discussing their findings, neither man wrote to the other about their theories of evolution. It was only when Wallace’s letter arrived that Darwin realized that they — two men, on opposite sides of the world, on totally different timelines — had come to the exact same conclusion.

Charles Darwin circa 1855 (left) and Alfred Russel Wallace circa 1860 (right). Credits: Bettmann (left) and Mondadori Portfolio (right) via Getty Images

In May 1857, Darwin wrote to Wallace to say, “I can plainly see that we have thought much alike & to a certain extent have come to similar conclusions […] I daresay that you will agree with me that it is very rare to find oneself agreeing pretty closely with any theoretical paper.” But this was something else. This letter, sent July 1, 1958, laid out Darwin’s theory exactly. “I never saw a more striking coincidence,” Darwin wrote to a friend two weeks after receiving Wallace’s letter. “If Wallace had my [manuscript] written out in 1842 he could not have made a better short abstract! Even his terms now stand as Heads of my Chapters.”

While Darwin’s process of arriving at the theory of natural selection, as detailed in his notes, came through careful study and chronicling of the world around him over a long period of time, Wallace was a more frantic scientist. Scholars believe Wallace formulated the majority of his theory in just three years. During that time, only one contemporary clue to his thought process exists. In a letter written a few weeks later, Wallace divulges his obsession with tiger beetles on the islands he visited, which matched the color and mud where they lived. This was too weird to be an accident, Wallace presumed.

Weirdly, though, it took the scientists different amounts of time to come to their conclusions. Both Darwin and Wallace claimed to have been inspired after reading Thomas Malthus’ 1798 book, Essay on the Principle of Population, which argued for population control, positing that while humans reproduce quickly and exponentially, food production could only increase arithmetically. (Malthus believed that the earth was capable of providing food only for something like 9 billion people, a problem modern-day scientists are already finding themselves in the midst of.) Darwin read this theory in 1838 and immediately began incorporating it in his own work, whereas Wallace didn’t read and see its relevance until 1846.

“It suddenly flashed upon me…in every generation the inferior would inevitably be killed off and the superior would remain — that is, the fittest would survive,” Wallace wrote. There it was: the theory that changed evolution. Wallace wrote it down and shipped it off to Darwin. They were two minds on the same track, pulling into the same place at the exact same time at wildly different speeds. Of course, neither of them understood why natural selection occurred. That discovery was made by Gregor Mendel and his pea plants, though it wouldn’t be realized as the aspect that eluded Wallace and Darwin for 30 more years.

Time, perhaps, is the greatest innovator. “Discoveries are offshoots of their time, rather than turning up altogether at random,” wrote sociologist Robert K. Merton, listing other scientific simultaneous discoveries, including calculus, the telephone, and the automobile. In this series, we’ll explore a few of those, but also how time creates trends in art and culture as well. Of all the simultaneous discoveries in history, though, natural selection remains unique. It is one of the only recorded examples of an idea that not only came to two people from the same inspiration but also was announced simultaneously.

Darwin was astounded to receive his exact theory from another scientist. Was he about to lose two decades of his life because a younger guy had gotten there more quickly? Darwin wrote to two fellow scientists — a geologist named Charles Lyell and a botanist named Joseph Hooker — to whom he’d shown early drafts of his own work. The two arranged for a paper containing this discovery to be read at a biology society meeting. The 18-page paper included an introduction from Lyell and Hooke explaining the extraordinary circumstances. “These gentlemen,” the paper began in earnest, “independently and unknown to one another, conceived the same very ingenious theory.”

And so they had. The reading went on to include some of Darwin’s unpublished manuscript, a letter from Darwin to a Harvard professor to show that Darwin had been having these thoughts for two decades, as well as Wallace’s letter in full.

Neither were present for the reading of the paper. Wallace was still on the other side of the globe, and Darwin was busy mourning the death of his 19-month-old son. The paper was published in a journal that month. The next month, Darwin published his long-worried manuscript as On the Origin of Species. The book immediately became popular, making Darwin a household name. It was that immediate popularity that rocketed Darwin into the history books — ahead of Wallace. In his book Darwinism, Wallace wrote, “[T]his vast, this totally unprecedented change in public opinion has been the result of the work of one man, and was brought about in the short space of twenty years!”

Wallace was also famous during his lifetime, but his name did not continue forward to the public after he passed. At the time of his death, in 1913, Wallace was still famous, but because he was not as successful (or lucky) as Darwin at reaching mainstream audiences, he was quickly forgotten. It was only a twist of fate or the happenstance of age that Darwin was older and further along in his theory by the time Wallace evolved to that same place. In a way, Darwin was simply the one we naturally selected.