The rapid expansion of males in the 55,000 to 50,000 year range probably represents a bettering of conditions after the severe cold and starvation that shrank the human population when the Toba supervolcano blew its top. This eruption left a crater 18 miles by 65 miles—larger than the Yellowstone basin—and a noticeable slump in the earth’s temperature record around 74,000 years ago.
The difference between Toba at 74000 and the so called increase at 50-55000 is too great a period to attribute that leap to Toba. 20000 years is time for 3 civilizations like our current one to come and go.
The human race recovered, after the dark winters of the Younger Dryas ended, in little more than than half that time - 12,000 years later we are again a worldwide civilization.