Julie, the trend-setting chimp.

Julie, the trend-setting chimp. Photo: Animal Cognition

Just in time for this year's primate-starring film event, the Dawn of the Planet of the Apes, comes news from Zambia that chimpanzees may have taken another evolutionary step forwards. Or at least one that makes them even more similar to us.

A piece of grass hanging out of one's ear may not look like much, but most trends don't until they catch on.

Especially this one, which has taken off among a group of chimpanzees in what may be the first fashion trend spotted in the animal world, according to a study published recently in science journal Animal Cognition

The behaviour appears to be "non-adaptive", ie, motivated by frivolous rather than functional reasons. Dutch primate specialist Edwin van Leeuwen describes it as "quite unique".

He first spotted the trend-setting chimp in 2010 when Julie, an elderly female, repeatedly popped long pieces of grass in her ear and left it there for several hours. 

The quirky idea was adopted by seven other chimps in her troop, who continue to do it after her death.

“The chimps would pick a piece of grass, sometimes fiddle around with it as to make the piece more to their liking, and not until then try and stick it in their ear with one hand,” Mr van Leeuwen told animal news website The Dodo.

“Most of the time, the chimps let the grass hang out of their ear during subsequent behaviour like grooming and playing, sometimes for quite prolonged times. As you can imagine, this looks pretty funny.”

Of the four groups living in the same grassy environment at a wildlife sanctuary in Zambia, only one group is experimenting with the look so far. This makes it more likely to be a non-functional flourish. 

Chimpanzees are social creatures who live in communities of up to 150 members but move about in close groups of fewer members.

These groups are fluid, with chimpanzees often switching groups, so the trend could potentially spread beyond the first unit.

Humans and chimps share more than 98 per cent of their DNA. Mr van Leeuwen says the closest human trends are hats or earrings.