In common parlance, "evolution", or backward evolution is the notion a species may evolve into more "primitive" forms. From a scientific perspective, devolution does not exist. Lay people may see evolution as "progress", reflecting the 19th century ideas of Lamarckism and orthogenesis, but modern genetically-based biological evolution theory asserts that evolution occurs by such mechanisms as natural selection, genetic drift, and mutation, and is therefore not directional, forward or backward in time; hence "devolution" is not a valid concept.