For Humans, with the advent of space travel came the need to perform tasks outside the controlled atmosphere of space vessels. Consequently, the EV suit was developed. As planets and other stellar objects came within the reach of Human space explorers, their EV suits became necessary for them to explore environments with different atmospheric conditions than those on Earth. (TOS: "The Naked Time" , et al.) Other cultures also used EV suits. (ENT: "Silent Enemy", "Breaking the Ice", et al.)