Humans have long had dreams of becoming immortal, or of greatly extending their life span. Author Jonathan Weiner has explored the science and pseudoscience of life extension in his book, "Long for This World: The Strange Science of Immortality." The writer asks the question if a much longer life is possible - or desirable.
Nothing in nature is immortal, but some clams can live centuries and a tiny freshwater creature called a hydra lives a very long time, at least until its pond dries up.
Can humans achieve the same? Weiner says they've always thought about it.
"If you look at the formative stories of so many civilizations, they're about reaching out to try to grasp immortality," he said. "Adam and Even and the apple and emperors in China and Gilgamesh in Babylon, again and again. And the Greeks. Hercules, in his labors, was trying to defeat death, again and again, because in some ways it's our primary task as mortals. It’s certainly our primary problem as mortals."
He says the quest for eternal youth has captivated some notable people in their middle age. In the early 20th century, a number believed that vasectomies could renew their failing vigor.
"Sigmund Freud and the great poet William Butler Yeats both went in for surgery to give them tremendously enhanced virility and youth in their older years," he said. "And that surgery was something that revivified Yeats. In fact, he had a tremendous flowering of poetry and around Dublin, they used to call him the 'gland old man.' "
The results for Freud were less certain. The operation was something the father of psychoanalysis avoided talking about.
The writer says scientists are not sure how far life can be extended, and that they debate the best way to extend it. Some focus on the separate problems of aging such as cancer, Alzheimer's and heart disease, while others search for the reasons the body breaks down at the cellular level.
In fact, we have extended our lives dramatically over the past century, and on average, live decades longer than our great grand-parents did. And more people today are living to be 100.
Still, most don't make it much past 80, and centenarians are a tiny part of the population.
The writer notes that our longer human life span in the 21st century is already creating social tensions, pitting young against old in debates over taxes, public spending and the retirement age in Europe and other places.
He asks how we would cope with the population explosion if couples produced babies for 100 years?
And he asks how longer life span would affect societies burdened with aging or evil leaders.
"Just imagine if Mao had been given an extra 50 or 60 years of healthy life, or Stalin," he said. "If Hitler had really had a chance at his thousand year Reich and a chance to rule it himself. Those are nightmares."
Would dramatic life extension be a violation of nature? Weiner says, not necessarily.
"If we could engineer ourselves some of the secrets of the clam or the hydra, then would we be doing something very different from what we do now when we get a flu vaccine, or when we get exercise sop that we will continue to live long, happy, healthy lives? I don't know that those answers are so clear," he said.
He says the most difficult problems do not confront us yet because scientists who want to extend our lives have not achieved the breakthroughs that they hope for.
Living forever is still a dream, the subject of myth and fiction, and many researchers hope to add a more modest 20 to 30 years to the average lifespan. The most optimistic hope to add hundreds of years, while skeptics say we may already be approaching our maximum lifespan.