Stephen Hawking Turns 76 Today—Here's How the Brilliant Physicist Has Defied the Odds of Fatal ALS Disease

Stephen Hawking was first diagnosed with ALS at 21. NIKLAS HALLE'N/AFP/Getty Images

Today is Stephen Hawking's 76 birthday and the famed physicist has once again proved his resilience against amyotrophic lateral sclerosis (ALS), the fatal and debilitating disease he was diagnosed with at age 21. And while we all worry about Hawking's health as he ages, the physicist has a more important concern on his mind: the survival of the human race.

Hawking is celebrating his birthday in quite an interesting manner. A new episode of his Emmy-winning series "Favorite Places" premieres tonight on, LiveScience reported. In the episode, Hawking narrates the exploration of Venus' atmosphere and surface, warning that Earth may soon look like our solar system neighbor if we don't do something quickly to address climate change.

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But as Hawking continues to explore the mysteries of the universe, the public can't help but be fascinated with the mystery of his personal longevity. According to the The ALS Association, only half of people affected with ALS live at least three or more years after diagnosis. Just 20 percent live more than five years, and a mere 10 percent make it beyond 10 years. For Hawking, today marks 52 years of living with the condition.

These past five decades have not been easy. Hawking is now completely confined to a motorized wheelchair and is unable to use most of his muscles. In 1985 Hawking lost the ability to speak and now has to communicate completely with a computer system.

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The reason for Hawking's survival is not easily explained. In 2012, Scientific American spoke with Leo McCluskey, associate professor of neurology and medical director of the ALS Center at the University of Pennsylvania, on the topic. He explained that Hawking truly is an oddity.

ALS is a progressive neurodegenerative disease, which means that the illness slowly destroys the nerve cells in the brain and in the spinal cord. As a result, sufferers slowly loss motor function, but still maintain cognitive function—they cannot physically move, but continue to think as a healthy person. Most ALS patients will either pass away from respiratory failure, as a result of loss of the diaphragm muscles, or from malnutrition and dehydration, as a result of failure of the swallowing muscles, Scientific American reported.

According to McCluskey, who has not treated Hawking personally but has an in depth knowledge of ALS pathology, Hawking's personal biology and the way the disease has progressed in his body likely has a lot to do with his personal longevity.

"If he really isn't on a ventilator, then it's his biology—it's the biology of his form of the neurodegenerative disease that determines how long he will live," McCluskey told Scientific American .

However, McCluskey admitted that as one of the most famous and celebrated scientists in the world, Hawking also likely has excellent personal care that could contribute to his good health.

Whatever the reason for Hawking's longevity, there's no mistake that scientists and layman alike are happy to wish the physicist a happy 76th birthday—and wishes for many more to come.