How Animals Use and Cope with Gravity

Since the dawn of life on Earth some four billions of years ago, gravity has been a more or less stable environmental factor thus influencing the phylogenetic development of all living organisms. On the one side, gravity represents a factor of physical restriction, which compelled the ancestors of all extant living beings to develop basic achievements to counter the gravitational force (e.g., elements of statics like any kind of skeleton from actin to bone to overcome gravity enforced size limits or to keep form). On the other side, already early forms of life possibly used gravity as an appropriate cue for orientation and postural control, since it is continuously present and has a fixed direction. Due to such a thorough adaptation to the Earthly gravity vector, both orientation behavior as well as the ontogenetic development of animals is impaired, when they have to experience altered gravity (∆g; i.e. hyperor microgravity). Nevertheless, animals still can cope with ∆g in a certain range based on their physiological plasticity, which varies among the different animal phyla.