[caption id="attachment_1046" align="alignright" width="275" caption="Forever Young: The Science of Aging"][/caption] An infant born in the U.S. today will probably live to see his or her 78th birthday, a 20- year-plus increase over the average lifespan a century ago. As living well into our 80s and 90s becomes more attainable, how many more years can humanity expect to gain going forward? The two main physiological barriers are accumulated damage to cells and organs and age-related illnesses such as cancer and Alzheimer's disease. Researchers are divided over where to focus their next efforts. In Scientific American's newest eBook, Forever Young: The Science of Aging, we take a look at what science knows--and what it's striving to learn--about the aging process. Both genes and environment influence how long people live and how well they age, as discussed in Section 1, "A Matter of Time: The Aging Process." The eBook opens with "Why Can't We Live Forever," in which author Thomas Kirkwood explains exactly why by way of his disposable soma theory. He postulates that because germ cells (sperm and egg) matter most, the human body makes a trade-off and diverts more energy to maintaining them over somatic (body) cells, leading to a buildup of DNA and protein mutations. Other theories of how we age, involving the roles of telomeres, free radicals and caloric restriction, are discussed in subsequent sections. Recent studies have called into question long-held beliefs about the anti-aging benefits of antioxidants and reducing caloric intake, as discussed in Melinda Wenner Moyer's "The Myth of Antioxidants" and Gary Stix's "Cutting Calories Might Not Mean a Longer Life," respectively. Amidst the many age-related illnesses, few are as emotionally devastating as Alzheimer's disease, to which the eBook dedicates a full section that examines some of the many clinical trials aimed at finding treatments. Finally, the eBook explores the quest for longevity, featuring stories on life-extension research and lifestyle choices. In particular, "Fit Body, Fit Mind?" looks at how to prevent age-related mental decline by staying physically fit and socially involved. So while there's no miracle pill on the horizon to extend our lives to 150, we can certainly make the most of the years we have. Click here to buy this and other Scientific American eBooks: http://books.scientificamerican.com/sa-ebooks/.