The effects of gravitational forces on reproduction and development

It is clear that increased gravitational forces can affect biologic reproduction and development, although exact mechanisms of action have not been established. Except for three studies of male pilot and astronaut fertility, human reproduction and development studies of chronic or acute exposure to micro- or hypergravity environments have not been carried out. Only two reproduction and development studies (both Soviet) have been done under chronic or acute exposure to microgravity. It is unlikely that chronic human exposure to hypergravity will occur except when planets much larger than Earth are colonized. Colonies dependent on reproduction for continued existence probably could not be established on planets with masses significantly dissimilar to Earth because hypergravity or hypogravity are likely to affect reproduction adversely and cause abnormal growth and development. Acute exposures to gravitational changes in the later stages of development appear to be less detrimental, but much remains to be discovered about how gravity affects reproduction and development of mammals, humans in particular. Earth's gravitational force has helped to shape human reproduction and development. Only when the limits of mammalian biology on both sides of 1 g are explored will we be able to determine the extent to which gravity determines biologic structure and function.