Have giant humans ever existed?

Humans have shared stories about giants for thousands of years, from the cyclopes of Greek mythology to the biblical Goliath. But are these just tall tales, or have giant humans really walked this Earth? 

If you consider a nearly 9-foot-tall human a giant, then yes. Robert Wadlow, the tallest person on record, grew to 8 feet, 11 inches (2.72 meters) before he died at the age of 22 in 1940, according to Guinness World Records. 

Wadlow was well above the current U.S. average male height of around 5 feet, 9 inches (1.75 m) and even taller than some interpretations of the biblical descriptions of Goliath. Still, there was nothing magical about Wadlow. As with most real-life giants, his stature resulted from a medical condition. 

"The majority of [giant] patients have a growth hormone problem," Márta Korbonits, an endocrinology professor at Queen Mary University of London, told Live Science. "That's what Robert Wadlow had."

Korbonits noted that the leading cause of gigantism is elevated levels of a growth hormone produced by the pituitary gland in the brain. Most of the time, these high levels are caused by a benign tumor. One reason it's unlikely we'll see another person as tall as Wadlow again is that doctors can now remove the tumor and use medications to halt growth, as gigantism and the tumor endanger a person's health. 

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Other conditions can cause people to be extraordinarily tall. These include Marfan syndrome, a genetic disorder that causes bones to grow longer, Korbonits explained.