As we reported earlier this week, NASA is recruiting "pillownauts", people willing to stay in bed for months at a time to observe the effects zero gravity will have on the body. And the results aren't pretty. Since you can float, little force is required to get around in space, leading to quick atrophy of muscles. Astronauts tend to lose bone mass fairly quickly making the body very brittle. The development of our circulatory system compensates for gravity, so without it blood starts pooling in strange places, like our heads. This leads to painful headaches, chronic congestion, and, given enough time, comically swollen heads. If the trip is extended into generational lengths of time, the results could become more severe. Muscles and bones may not develop correctly, making space babies short and fat. And living in filtered and climate-controlled environments could lead to an evolutionary phase-out of hair, which primarily functions to maintain body warmth and protect from foreign particles.