How long do you want to live, and why? These are the questions that bestselling author and science writer David Ewing Duncan asks in the new TED ebook, When I’m 164: The New Science of Radical Life Extension, and What Happens If It Succeeds. Duncan examines the increasingly legitimate science of radical life extension — from genetics and regeneration to machine solutions — and considers the costs and benefits of living to 164, or beyond. The book also considers the impact of extended life on cities, services, and the cost of living as well as what happens to love, curiosity, and general health. We recently spoke with Duncan to ask him a few questions about the ideas underlying the book.

In terms of life extension, what is reasonable to expect in the next few decades? How many years can we add to the average life?

To answer this, let’s first consider that human lifespan at least in the west has nearly doubled since the late nineteenth century, from under 40 years old to nearly 80 years old. This is due primarily to better hygiene and nutrition, but also to a more than a century of extraordinary advances in bioscience and medtech — everything from antibiotics and heart bypass surgery to new targeted drugs for cancer. According to the United Nations, within a century the average life expectancy in the west will jump to nearly 100 years.

Added to this steady upward tilt in aging is a range of new technologies – genetics, stem cell therapies that regenerate tissue, and bionics – that may provide an even bigger boost more quickly. How big a boost is open to debate, with serious scientists giving ranges from a few years to a few decades. When these lifespan-boosts will be available is another question that gets a wide range of answers, with some saying within 10 to 20 years and more saying more like 40-50 years. But few doubt that one of the new technologies or more will succeed.

What breakthroughs are most important to these developments?

The book describes four main areas — healthy living and predictive and preventive medicine; genetics; regeneration; and machine solutions.

Healthy living already has increased lifespans and prevented death for literally billions of people over the past 150 years, but we could still do more, especially to combat lifestyle conditions and diseases like obesity and diabetes, which prematurely kill millions of people a year. The science of predictive medicine is moving fast to help set up profiles for individuals and populations that can assess a person’s DNA and a wealth of other biomarkers that can be used to determine future risk factors that may, in many cases, be acted on to prevent or mitigate disease.

For genetics, mainstream scientists for 30 years have been studying and trying to better understand the process of aging at the genetic and cellular level, as well as in entire organisms. They have succeeded in manipulating genes and proteins that seem to regulate lifespan in worms, flies, mice and other critters — sometime upping lifespan by many times. More importantly perhaps, they slow the aging process by delaying or preventing diseases of aging like heart disease and diabetes. Several drug companies are developing drugs for conditions like diabetes and inflammation that activate enzymes linked to increased lifespans in mice and other animals, and may work in bumping up lifespans for humans, too. At least one of these pills, a compound that treats inflammation being tested by GlaxoSmithKline, is in Phase II human testing (out of 3 phases for FDA approved drugs). If successful, it could be on the market in under 5 years.

For regeneration, scientists have succeeded in using stem cells – the special cells that replace dying cells in different organs – to regrow or repair hearts, livers and other tissue in animals. They have some success in regenerating tissue in humans, but only for simple organs like a bladder or bone marrow. Using stem cells to regrow, say, cells in the heart or brain remain many years in the future, say scientists.

For machine solutions, humans have long fused machines or engineered devices and tools to their biology to improve or treat conditions or maladies. These include everything from eyeglasses to pacemakers and joint replacements. More recently, inventions and breakthroughs are already linking devices to the brain to help patients with Parkinson’s Disease control tremors and to help some people who are deaf to hear again. Other experimental machine-brain interfaces may soon allow the paralyzed to operate computers using thought.

In your research you discovered nearly universal rejection of immortality. Surprising; most people don’t want to live forever?

For the past 3 or 4 years I’ve been asking a question at the start of most of my talks: How long do you wan to live? I’ve kept track of the show of hands and over time have polled some 30,000 people. I asked people to vote on one of four answers: 80 years; 120 years; 150 years; or forever. It was a surprise to me that 60 percent of the people want to live the current average life expectancy in the West – about 80 years. Other results: 30 percent want to live to age 120; less than 10 percent to age 150; and less than one percent forever. I told people not to assume there was a scientific “fix” allowing them to live longer – although they were free to imagine there was such a fix – or not.

I encourage people to vote for their preferred lifespan on the book’s website: whenim164.com. A chart keeps the percentages voting for each “age preference” up to date.

You’ve done a lot of first-person reporting on life extension techniques. What’s the oddest test you ever took in your research?
The most intriguing was a test by the drug company Sirtris (now owned by GSK) that tested the levels of an enzyme inside me that is associated with longer lives and better health in a number of animals, and may work to extend lifespan in humans. Called SIRT1, this enzyme only works if activated – probably by times of stress when people can’t get enough to eat (this is called caloric restriction – one hypothesis is that SIRT1 is activated during famine to keep cells and organisms in good health to get them through the crisis so they can live to reproduce). It turns out that I “over-express” this enzyme by almost 1,000 times compared to others tested. This may explain the longevity of my family. It also might deliver a greater than average bump should I take the drug Sirtris is testing in human trials right now – which acts by activating SIRT1.

What are the upsides and downsides to living much longer? 

For the book I asked hundreds of people why they voted the way they did in the “how long do you want to live” survey. Here are the eight primary reasons people voted to live to the ages of 80 or 120, and not longer:

• Fear of prolonged frailty
• Money: how to pay for an extended life
• Life is hard
• Wars, plagues and poverty
• Overpopulation, resource depletion and the environment
• Love and relationships
• Boredom
• We would cease to be human

As for those respondents who said they want to live to 150 years or beyond, their stated reasons for wanting to live radically longer than current human life expectancy fell into five broad categories:

• More time with loved ones
• Geniuses would still be alive
• Want to know the future
• More to do and accomplish in life
• Avoiding the frailty of old age

As you can see, prolonging life can be both a blessing and a burden. But few doubt that we are at the cusp of an age that will see humans able to live much longer lives.

When I’m 164: The New Science of Radical Life Extension, and What Happens If It Succeeds is part of the TED Books series.