The theory that states that life can only arise from existing life is known as biogenesis. This concept contrasts with the idea of spontaneous generation, which suggested that life could originate from non-living matter. Biogenesis posits that all living organisms are derived from pre-existing organisms through processes such as reproduction. This theory gained substantial support through experiments by scientists like Louis Pasteur, who demonstrated that microorganisms did not spontaneously generate but instead came from other microbes. The biogenesis principle is fundamental in understanding the origins of life and the continuity of biological species.