In the year 1831, two very important events happened to 22-year-old biologist Charles Darwin.

The first was that he boarded the Beagle, a research vessel upon which he would embark on a five-year journey to Central and South America. There he would collect mountains of data on hundreds of plant and animal species, which he would then use to develop his theory of evolution by natural selection – the cornerstone of modern biology.

The second event was that – just before boarding the Beagle – he fell extremely ill.

Darwin kept his condition secret for fear of being removed from the passenger list. But this early bout of illness was just the beginning in a series of ailments that would continually affect nearly every aspect of Darwin’s life for the next 40 years.

The Symptoms

The list of symptoms that plagued Darwin for the majority of his adult life included everything from chronic fatigue, severe abdominal pain, nausea and vomiting, headaches, insomnia, mouth ulcers, boils, anxiety, heart palpitations, and depression (just to name a few). In his many letters to friends and colleagues, he constantly mentioned the wretched state of his health.

“I have been [for] five or six wretched days miserable from morning to night and unable to do anything,” Darwin wrote in 1865 to naturalist and friend William Hooker.

Just a year earlier he had told Hooker, “for five months I have done nothing but be sick.”

His illness often precluded him from many public lectures and events expected of eminent scientists of the time. His wife, Emma, tried to care for Darwin, as did numerous physicians, but his poor health remained until his death in 1882.

The importance of Charles Darwin as a father of modern biology, combined with the complex and intriguing nature of his chronic illness, have led to many hypotheses as to why he suffered as he did.

Everything from heart disease to arsenic poisoning to a variety of psychosomatic causes has been proposed since his death. However, it is only within the last several years that these hypotheses have focused on the gastrointestinal symptoms that seemed to plague Darwin most consistently. Unable to examine the man himself, scientists have pored over his medical records, letters, and personal diaries, in order to posthumously diagnose Darwin’s debilitating illness.

The Case for Lactose Intolerance

During the mid-19th century, lactose intolerance had not yet been described in great detail. Most gastrointestinal problems were written off as ‘indigestion’ or ‘dyspepsia’. Indeed, the genetics of lactose intolerance would not be discovered until more than 70 years after Darwin’s death.

People diagnosed as lactose intolerant often suffer severe lower abdominal cramping and diarrhea after consuming milk or other dairy products (including some cheeses and various kinds of cream). Because the majority of Darwin’s symptoms appear to be centered around the digestive tract, a group of researchers from Cardiff University proposed in 2005 that the best explanation for Darwin’s symptoms was lactose intolerance.

It is far more common to find lactose intolerance among South and East Asian populations, though it is not unheard of to find it among Europeans, where it reaches levels of about 8%. Researchers, digging through his written correspondence, have found many key passages that hint at Darwin being lactose intolerant. For example, in 1865, Darwin wrote to H.B. Jones, his physician, recounting that “on most days, three hours after luncheon or dinner I have a sharpish headache on one side, and with bad flatulence last to the next meal.” He also wrote to his friend and colleague, William Hooker, “I have had a bad spell. Vomiting every day for eleven days, and some days after every meal.”

An analysis of his Diary of Health indicates that foods such as sugar, bacon, butter, and any desserts seemed to intensify his symptoms. Unfortunately, Darwin had a sweet tooth, and the majority of his wife’s recipes involved heavy cream. To make matters worse, when Darwin was feeling particularly ill he was often given warm milk as a nightcap, a typical remedy during the mid-19th century. This may have exacerbated his abdominal pain and discomfort.

In fact, the only treatment that appeared to work was something called “hydrotherapy” in which the patient bathed and drank copious amounts of cold water. Milk was not allowed. This, some argue, is additional evidence in support of lactose intolerance being the primary cause of Darwin’s symptoms.

The Case for Crohn’s Disease

However, while most agree that the majority of Darwin’s symptoms were gastrointestinal in nature, some remain unconvinced that the best explanation was that Darwin was lactose intolerant. Instead, they point to a more serious disorder known as Crohn’s Disease. This new diagnosis is garnering much support within the medical community, in that Crohn’s — even more so than lactose intolerance — accounts for the vast majority of Darwin’s incapacitating symptoms.

Crohn’s disease is a chronic autoimmune disease of the digestive tract. It is found in about 1-2% of people of European descent and can affect an individual’s entire digestive system, from the mouth to the anus and everything in between. Additional symptoms include skin rashes, arthritis, and inflammation of the eye. It usually first presents itself in early adulthood as a severe gastrointestinal infection. Individuals suffering from the disease often have a series of flare-ups and remissions throughout their lives. Crohn’s disease is believed to be a largely genetic disorder, though not all genetic markers have been identified.

Various factors can influence the timing and frequency of flare-ups for sufferers of Crohn’s, including stress, nutrition, and other health issues. Indeed, Darwin often noted worsening symptoms during periods of high stress, especially when he had to give public appearances or lectures.

Upon close examination of Darwin’s correspondence and diaries by scientists at the University of Chile, his most severe symptoms included abdominal pain and vomiting, but virtually no mention of diarrhea, which is the main symptom of lactose-intolerant individuals. In fact, Darwin had reported regular bowel movements for the majority of his adult life. It was the abdominal pain, nausea, and vomiting that plagued him for so many years, and these symptoms are key when diagnosing Crohn’s Disease.

In addition, and perhaps more importantly, Darwin had several other health issues seemingly unrelated to the digestive tract, namely skin, and eye irritation. Symptoms such as these are often found in patients diagnosed with Crohn’s Disease. And the fact that there are conflicting reports on the kinds of foods that upset his illness (Darwin also reported getting sick after eating sugar, bacon, and salads), lends additional support that his illness was not related to a specific type of food (i.e. dairy).

There is, of course, the possibility that Darwin suffered from both lactose intolerance AND Crohn’s Disease. In fact, there is an 83% chance that individuals with Crohn’s Disease are also lactose intolerant. However, the reverse is not also true, meaning the root cause of lactose intolerance among people with both conditions usually traces back to their Crohn’s.

It also appears that there is some genetic aspect to Darwin’s illness, as many of his family members suffered chronic health problems. In fact, the Darwin family was famous throughout the 19th and early 20th centuries as having overall poor health. Darwin’s family history points to some kind of genetic disorder, and the symptoms of Crohn’s disease appear to be the most comprehensive explanation.

The mystery surrounding Darwin’s chronic illness has mystified researchers for over 100 years. If he were alive today, it is likely that physicians would have no trouble diagnosing what ailed him.