World population and stresses on the environment, with guest scientist Danielle Nierenberg of Worldwatch Institute. Also: New evidence that nuclear technology is proliferating around the world; Astronomers announce 4 new extra-solar planets in just one week; Scientists find fish, soy, and other foods rich in Omega-3 fatty acids can reduce incidence of Alzheimer’s Disease; How dangerous are whole-body cat scans?; One doctor says you can decrease your chance of getting heart disease by 90% if you eliminate 9 risk factors.