John Maler Collier, via Wikimedia Commons

It’s an enduring mystery and much-debated. He suffered fifty years of chronic ill health, including nausea, headaches, dizziness, insomnia, depression . . . the list goes on and on.

Various theories range from physical maladies such as malaria, Chagas, ulcer, and gout to psychological issues, including hypochondria and general agoraphobia (fear of leaving the house).

If you happen to have just finished writing a book about insects (like me), you probably subscribe to the theory that he contracted Chagas Disease. He describes being attacked by assassin bugs in his diary written while aboard the Beagle, and many of his symptoms of chronic ill health are consistent with Chagas.

If you happen to have written a book about arsenic, as James Whorton masterfully did, you may believe that Darwin’s lifelong poor health may have been made horribly worse by his doctors, who treated him with arsenical medicine, the notorious Fowler’s solution. Arsenic may have been what ultimately killed him.

I asked Deborah Heiligman, author of the lovely biography, Charles and Emma, what she thought, and she believes it was probably a combination of things, including lactose intolerance and general anxiety about publishing.

And as Georgia Bragg points out in her hilarious and informative book, How They Croaked, it didn’t help matters that he spent years in his laboratory, breathing in formaldehyde, working with dead animal specimens, and taking virtually no precautions to ventilate his workspace or wear protective clothing.