Sport and society remain stuck in the "stone age" when it comes to women's rights, Formula One champion Lewis Hamilton said on Thursday.
Hamilton, who was 12th on the Forbes annual list of the world's highest paid athletes released this week, was asked his thoughts on the total absence of women in the top 100.
He says women, in sport or business, should earn equal pay for equal work and questioned the absence of tennis player Serena Williams from the Forbes list.
"(It) just shows you how behind we are in the world," Hamilton said.
"There is no reason women should not be able to earn what men are able to earn.
"Serena is in the top three of the greatest athletes of all-time above a lot, if not all, that are on that list so it is big, big question, why?
"Women rule the world. I don't understand.
"It just shows you we are still in the stone age. That needs to change."
Williams, a 23-times grand slam singles champion, had been ranked 51st on last year's Forbes list, but dropped out of the top 100 after taking time away from the sport to have her first child.
Tennis offers equal prize money to men and women, but many other sports have not come close to keeping pace when it comes to pay and diversity.
"Serena has already spoken of how difficult it is," said Hamilton. "It is going to take some time to change it."