Final answer:
Heavy metal and progressive rock were the two genres that developed in the aftermath of The Beatles' psychedelic period.
Step-by-step explanation:
The two genres that developed in the aftermath of The Beatles' psychedelic period were heavy metal and progressive rock.
Heavy metal, characterized by its loud and aggressive sound, emerged in the late 1960s and early 1970s. Bands like Black Sabbath and Deep Purple incorporated elements of blues and psychedelic rock to create a heavier and more intense style.
Progressive rock, also known as prog rock, arose in the late 1960s and continued into the 1970s. Bands like Pink Floyd and Yes combined traditional rock elements with complex compositions, extended instrumentals, and philosophical lyrics, pushing the boundaries of rock music.