The 72-year-old actor explained his dietary theory as to why Irish men have luscious locks when asked how his own mane looks so good and noted that his father Tom "had good hair".
Speaking to Page Six at the premiere of The Thursday Murder Club, Pierce said: "I don't know.
"It's all in the hair, the old Celtic hair."
The former James Bond actor suggested that "potatoes, butter" or "the Guinness" is responsible for the lack of baldness in Irish men of a certain vintage.
When told that he was ageing like fine wine, Brosnan replied: "I'm doing my best!"
Brosnan plays retired trade unionist Ron Ritchie in the upcoming Netflix murder mystery film The Thursday Murder Club - based on Richard Osman's novel of the same name - but explained that it isn't the first instance of him taking on a character who is "rough-around-the-edges".
"I've done rough-around-the-edges before," he said.Â
"(I've) been so entrenched in the world of the sophisticated man and Mr Slick and Mr Elegance, you know, sometimes you paint yourself into a corner with your own ... you get hoisted by your own canard so to speak!"
However, Brosnan pointed out that playing suave roles hasn't served him too badly, playing James Bond in four films between 1995 and 2002.
"It's paid the rent over the years!"
Brosnan has been praised for his recent role as crime boss Conrad Harrigan in the Paramount+ series MobLand and is delighted that the show has been received so well.
"I've been hearing that yes, for sure. One can feel the wave, and you celebrate it and give thanks, doesn't happen that often!"
Meanwhile, Brosnan has encouraged whoever is cast as the next James Bond to "be bold" and "have a great time" in the role.
"Be bold. Enjoy it. Know yourself, be strong, go out there and have a great time," he told Extra.
"There's so many wonderful actors. It's a magnificent role. Whoever finds the role, it will change their life."
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