A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment. Such fact-supported theories are not "guesses" but reliable accounts of the real world.
A scientific theory is best defined as substantiated explanation of some aspect of the natural world that is acquired through the scientific method and repeatedly tested and confirmed, preferably using a written, pre-defined, protocol of observations and experiments.
The theory of evolution was proposed by Charles Darwin and was first formulated in his book, "Origin of Species" in 1859. It focuses on the changes in species and populations over time
