On August 29, 1831, Charles Darwin returned home from a geology field trip in North Wales to find a letter waiting for him from his Cambridge professor and mentor, John Stevens Henslow. It contained an invitation to voyage around the world as a naturalist on the HMS Beagle, scheduled to leave a month later.
Although Darwin immediately accepted the offer, his father strongly opposed the idea, saying the plan was rushed, reckless, and detrimental to Darwin Jr.'s career prospects as a clergyman. The 22-year-old didn't take no for an answer, though. The next day, he rode some 50 kilometers from his home in Shrewsbury to Maer Hall to visit his uncle Josiah Wedgwood. If anyone could sway his father's heart, it was uncle "Jos," he figured. Darwin relayed his father's objections and pleaded his case.
Wedgwood sided with young Darwin. On August 31, Darwin wrote to his father begging him to reconsider his stance. In the letter, Darwin listed his father's eight principle objections as he understood them (pictured here), and included a note from Wedgwood, in which the uncle responded to each objection, point-by-point.
The letter changed his father's mind and the future of Darwin's life. Indeed, it was on that particular voyage that Darwin conceived the first glimmering of his theory of evolution, which he described in On the Origin of Species, published 150 years ago (February 12 is also the 200th anniversary of Darwin's birth). "If he hadn't gone [on the HMS Beagle], I think it would have posed a real problem, psychologically," says David Kohn, general editor of the American Museum of Natural History's Darwin Digital Library of Evolution. "That could have been a cause of bitterness and that might have disrupted him in pursuing his studies."