Animals are constantly exposed to external forces, including tactile stimuli from objects and living creatures, gravity, and air pressure. Among these, gravity is a constant, unavoidable force, and animals use it for various purposes, such as own-posture detection and behavior regulation. The signaling pathways of gravity perception are similar to mechanical-force sensing, and they are well conserved throughout evolution. On the other hand, structures and location of gravity receptors vary between animal species depending on the environment the animal inhabits. Thus, comparisons of gravity receptors together with the effect of gravity on each animal species lead us to a deeper understanding of how animals adapt to their environments. Here, we focus on the structures of gravity receptors and on animal responses to directional change of gravity caused by postural changes. We also introduce the effect of low/high gravity on animal development and physiology.