In the middle of the 16th century,
a talented young anatomist named Andreas Vesalius made a shocking discovery:
the most famous human anatomy texts in the world were wrong.
They not only failed to account for many details of the human body,
they also described the organs of apes and other mammals.
While Vesalius knew he was right,
announcing these errors would mean challenging Galen of Pergamon–
the most renowned physician in medical history.
But who was this towering figure?
And why did doctors working more than 1,300 years later so revere and fear him?
Born in 129 CE,
Galen left home as a teen to scour the Mediterranean for medical wisdom.
He returned home a gifted surgeon with a passion for anatomy
and a penchant for showmanship.
He gleefully entered public anatomy contests,
eager to show up his fellow physicians.
In one demonstration,
he caused a pig to lose its voice by tying off one of its nerves.
In another, he disemboweled a monkey and challenged his colleagues to repair it.
When they couldn’t, he did.
These grizzly feats won him a position as surgeon to the city’s gladiators.
Eventually, he would leave the arena to become the personal physician
to four Roman Emperors.
While his peers debated symptoms and their origins,
Galen obsessively studied anatomy.
He was convinced that each organ had a specific function.
Since the Roman government largely prohibited working with human cadavers,
Galen conducted countless dissections of animals instead.
Even with this constraint,
his exhaustive investigations yielded some remarkably accurate conclusions.
One of Galen’s most important contributions
was the insight that the brain, not the heart, controlled the body.
He confirmed this theory by opening the cranium of a living cow.
By applying pressure to different parts of the brain,
he could link various regions to specific functions.
Other experiments allowed him to distinguish sensory from motor nerves,
establish that urine was made in the kidneys,
and deduce that respiration was controlled by muscles and nerves.
But these wild experiments also produced extraordinary misconceptions.
Galen never realized that blood cycles continuously throughout the body.
Instead, he believed the liver constantly produces an endless supply of blood,
which gets entirely depleted on its one-way trip to the organs.
Galen is also credited with solidifying the popular theory of the Four Humours.
Introduced by Hippocrates centuries earlier,
this misguided hypothesis attributed most medical problems
to an imbalance in four bodily fluids called humours.
To correct the balance of these fluids, doctors employed dangerous treatments
like bloodletting and purging.
Informed by his poor understanding of the circulatory system,
Galen was a strong proponent of these treatments,
despite their sometimes lethal consequences.
Unfortunately, Galen’s ego drove him to believe that
all his discoveries were of the utmost importance.
He penned treatises on everything from anatomy to nutrition to bedside manner,
meticulously cataloguing his writings to ensure their preservation.
Over the next 13 centuries,
Galen’s prolific collection dominated all other schools of medical thought.
His texts became the standard works taught to new generations of doctors,
who in turn, wrote new essays extolling Galen’s ideas.
Even doctors who actually dissected human cadavers
would bafflingly repeat Galen’s mistakes,
despite seeing clear evidence to the contrary.
Meanwhile, the few practitioners bold enough to offer conflicting opinions
were either ignored or ridiculed.
For 1,300 years, Galen’s legacy remained untouchable–
until renaissance anatomist Vesalius spoke out against him.
As a prominent scientist and lecturer,
his authority influenced many young doctors of his time.
But even then, it took another hundred years
for an accurate description of blood flow to emerge,
and two hundred more for the theory of the Four Humours to fade.
Hopefully, today we can reap the benefits of Galen’s experiments
without attributing equal credence to his less accurate ideas.
But perhaps just as valuable
is the reminder that science is an ever-evolving process,
which should always place evidence above ego.