Humans are moving towards a day when there are space colonies in orbit, on the Moon, and the planet Mars, places where the force of gravity ranges between zero and 38% of what we experience every day. What effect will such different environments have on the regeneration of liver, skin, and other human body organs? To discover how the remarkable ability of Planaria flat worms to regenerate amputated body parts functions in a weightless environment researchers at Tufts University compared a group of whole and amputated flat worms which had lived for 5 weeks on the International Space Station with control groups which remained behind on planet Earth. The space faring flatworms were found to have undergone metabolic and other body function changes which persisted after they returned to Earth. Strangely one of the amputated worm fragments sent into space developed into an extremely rare double headed worm. Researchers were astonished since they had not seen this happen once during 5 years of observations of 15,000 worms. Further when both heads were removed from the space traveling double headed worm's middle section it grew 2 heads indicating that its body modification plan was permanent. The implications of these experiments for humans in space, if any, remain to be determined. Bottom line is we just don't know enough about how human reproduction and development will work off the Earth to plan on having permanent sustainable colonies elsewhere.