Biology has changed a lot over the past 150 years. Scientists have discovered entirely new forms of life, deciphered the molecular code of heredity and observed the machinery of life on the smallest dimensions. And through it all, one scientific theory has stood the test of time.

New discoveries in genomics, medicine, developmental biology, and countless other fields could have derailed the the theory of evolution. But the core principles of evolutionary theory, proposed by Charles Darwin 150 years ago, have remained among the strongest explanations of the natural world ever published.

In honor of Darwin Day 2009, which celebrates the 200th anniversary of Charles Darwin’s birth and the 150th anniversary of the publication of his seminal work, On the Origin of Species, we’d like to take a look at how evolution has itself ‘evolved’ over the decades — how new advances in science and technology have both reinforced Darwin’s original idea and given us insight into the inner workings of the theory that explains so much about the world in which we live.

In 1859, the phrase ‘evolution by natural selection’ was already beginning to make the rounds among the scientific elite in Europe and in America.  This was the year Darwin published On the Origin of Species, and his ideas about how species change over time were causing heated debate among the experts.  But Darwin didn’t invent the idea of ‘evolution’ (that is, the idea that species change over time).  What he brought to the table was an explanation of how species change, a process Darwin called ‘natural selection.’  On his famous journey to the Galapagos Islands 25 years earlier, Darwin had witnessed unique variation in hundreds of species.  As he pored over his notes for the next two decades, Darwin pieced together the notion that species must adapt to environmental pressures (like changes in climate or a volcanic eruption), in order to survive.  If they did not adapt to these pressures, then they may not survive.  It was natural selection, Darwin argued, that was the basis for the vast differences we see in plant and animal species across the globe.

But there was a lot that Darwin did not know when he published his ideas of evolution.  He did not know, for instance, how changes in a species’ appearance (a longer beak, a bigger shell, or a thicker coat of fur) are passed down from generation to generation.  The idea of discrete units — ‘genes’ that are passed down from parents to children — had not even occurred to Darwin, nor to most of the other scientists of the time.  Even when, in 1866, an Austrian monk named Gregor Mendel reported his ideas on patterns of inheritance in pea plants in the obscure Proceedings of the Natural History Society of Brünn, few took notice.

In fact, the word ‘genetics’ wasn’t coined until 1905, by biologist William Bateson. Bateson, who is sometimes credited with ‘rediscovering’ the lost works of Mendel, helped to usher in a new wave of research and discovery — this time looking at how species differ from each other at the molecular, or genetic, level.  Bateson’s push for the use of genetics in evolutionary research reached fruition in 1952, when Cambridge scientists James Watson and Francis Crick decoded the structure of DNA. Soon others discovered how specific genes are passed down from generation to generation, and how changes in our genetic code are connected to changes in species.  As each new genetic discovery allowed us to better understand the natural world at a microsopic level, Darwin’s theory of evolution by natural selection was continually reinforced.

The evolution of our species, Homo sapiens, forms the basis for virtually everything we can learn from 23andMe’s Personal Genome Service^TM.  The signature of millions of years of evolution is present in every person’s genome, and often in our physiology, rendering some of us resistant to malaria, others unable to digest milk, and even causing some to have lower risks of cancer or other diseases.  As advances in science and technology continue to bring us more information hidden within our genes, we can be thankful that 150 years ago, an amateur naturalist from Shrewsbury, England, boarded a ship bound for South America and began piecing together the evolutionary story of not just our species but of all life on earth.

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Put on your party hat.  Tomorrow, in universities and public auditoriums, at festivals and museums, people around the world will be celebrating the life and works of one of the most influential scientific minds in history:  Charles Darwin.  February 12th is Darwin’s 200th birthday, and this year – 2009 – also marks 150 years since the publication of his most famous work, On the Origin of Species.  Darwin’s works have – time and again – played a key role in advancing scientific thought in such fields as biology, genetics, biochemistry, and paleontology (just to name a few!).

The life and works of Darwin have been deemed so important by scientists from around the world that hundreds of museums, organizations, and scientific societies have decided to celebrate his birthday and his research.  Here are some of the notable events planned in celebration of Darwin, his life, and his contributions to the field of science.

National Academy of Sciences: Two Centuries of Darwin

The National Academy of Sciences of the United States, a prestigious scientific honors society that provides advice to the nation’s leaders on all topics related to science and technology, has revamped its resources on evolution in honor of Darwin Day.  In addition, it is hosting a series of events to honor Darwin and his scientific works.  The Academy is sponsoring a lecture series centered around the importance of evolution in advancing medical research. The lecture series will be held in Washington, D.C., but it will be streamed online to anyone who wishes to learn more about this fascinating topic.

Celebrations on the Newsstands

Many major scientific publications, including Science , Nature , National Geographic, and The Lancet, have released special issues in honor of Darwin’s work.  Science has also begun publishing a blog, Origins, which tackles some of the most fascinating aspects of modern evolutionary theory.  Each of these journals has chosen a specific aspect of evolutionary theory to discuss, giving us deeper insight into the mind of Darwin and how scientific research has progressed over the last 150 years.

University of Cambridge:  Darwin 2009

Darwin’s alma mater – Cambridge University – is particularly excited about Darwin Day.  The institution has planned several days of activities throughout the town and university, though we’ll have to wait a bit longer to celebrate.  Cambridge is organizing the bulk of the festivities for July, where – over five days – the town will be transformed into a celebration of scientific thought.  Organizers and volunteers have planned dozens of lectures, film showings, tours, exhibitions, and workshops.  Such well known scientific personalities as Richard Dawkins, Richard Leakey, and Sir David Attenborough will be presenting their take on the importance of Darwin and the importance of evolution.  It is sure to be an exciting festival – so start booking flights now!

There are in fact several hundred Darwin Day-related events going on during all of 2009, with many beginning this week.  Be sure to check the official list of Darwin Day 2009 activities in your area.

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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 Darwin’s life for the next 40 years.

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.  In 1865, he wrote to noted naturalist and friend William Hooker, “I have been [for] five or six wretched days miserable from morning to night and unable to do anything.”  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 have 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 everyday 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. And it’s too bad Darwin couldn’t sign up for 23andMe’s Personal Genome Service ^TM! Not only would the father of modern biology be fascinated by his genetic data, but it might have offered a clue to his lifelong illness as well by revealing whether he had a higher risk for lactose intolerance, Crohn’s Disease, or perhaps some other condition.

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