Who proposed the mutation theory of evolution? Explain it.

(N/A) In $1901$,Hugo de Vries carried out experiments on the evening primrose plant ($Oenothera$ $lamarckiana$) and proposed the mutation theory of evolution.
This theory states that evolution occurs due to sudden,large differences (mutations) in a population.
He believed that mutation is the primary cause of evolution,rather than the minor heritable variations that Darwin discussed.
Mutations are random and directionless,whereas Darwinian variations are small and directional.
For Darwin,evolution was a gradual process,while de Vries believed that mutation caused speciation,which he termed as saltation (single-step large mutation).
Later studies in population genetics provided further clarity on these mechanisms.