In the Olympic village, the evolution of the species happens overnight.
The second weekend of the Olympic Games marked a watershed, the sudden transformation of some of the most dedicated and competitive men and women into party animals who just want to have fun.
The final week is the point where having a rower or a swimmer as a neighbour no longer seems such a good idea.
For them, the games are over. Their events are done, the golds won and now - like the exhortations to crowds all over the Olympic Park - is the time to join the spectators and make some noise.
British rower Mark Hunter, the 2008 Olympic champion in the lightweight double scull who won a silver on Saturday, was asked what his future held.
"A lot of partying and getting drunk next week, it's the Olympic Games, it's time to have fun and socialise in the second part of the week," he replied.
"It's way too early to think about anything beyond that. It's about supporting team GB now and getting up the medal table with other sports and seeing what we can achieve as a team."
Compatriot Peter Wilson, who bagged a shooting gold, declared he was "going to get very, very drunk and perhaps do something silly".
Bradley Wiggins, winner of the Tour de France and the Olympic cycling time trial, has already posted on Twitter a picture of himself with a vodka and tonic in hand and the words 'Blind drunk at the minute'.
"They'll be out and getting on it and coming back and pissing all the athletics (people) off, because they're all trying to do their competition and stuff," he said of the swimmers in an interview with Absolute Radio on Sunday.
The streamlined swimmers, used to hours and hours in the pool each day, do have something of a reputation when it comes to letting off steam.
Twelve years ago, on the eve of the 2000 Sydney Olympics, triple jump world record holder and the eventual Olympic champion Jonathan Edwards, famously told reporters what he thought of some of his fellow competitors.
"The swimmers are awful. They finish their competition and stay in the village and party for the rest of the Games," he said.
"Ninety per cent of them can't win medals, they are there to have fun. If my sleep is interrupted by the swimmers coming back at 2 am from a party because they are finished, I might be tempted to move out of the village."
Then there is sex. At the Sydney Games, the supply of free condoms ran out. This time, organisers have made 150,000 available.
Stories of wild activity, even in a village where alcohol is not available, are the stuff of Olympic legend. The media are not allowed in and, like Las Vegas, the word is that what happens in the village, stays in the village.
"I'd say it's 70 to 75 percent of Olympians," champion US swimmer Ryan Lochte told ESPN magazine before the Games when asked how much sex went on in the village. "Hey, sometimes you gotta do what you gotta do."
Managing the arrival of a new tribe in the village, and making sure other competitors are not inconvenienced, becomes an issue for teams and organisers alike.
Colin Moynihan, a silver medal winning Olympic cox who competed in the 1980 and 1984 Games and is chairman of the British Olympic Association, told Reuters that the situation was all in hand.
The British rowers had partied on Saturday, but down by the water near the competition venue where they also stayed before moving to the village in east London on Sunday.
"In my experience in two Olympic Games, it is Saturday night of the first week where that is the biggest challenge for team management so we were well prepared for that," said Moynihan.
"The rowers and swimmers know how to celebrate and we plan for that.
"Going back to my time, in Moscow and Los Angeles, we had fantastic parties with the swimmers when we finished. It's much better organised now. There's much more attention to looking after the rest of the athletes."
For the British, that means having a quiet location in the village away from the social hubs. All team members have also signed up to core values, which include respect for others. Moynihan said he expected no troubles.
"There is a lot of detail that has gone into the planning, making sure that where people have finished and are coming into the village they are supportive rather than distractive of those athletes who have still to compete," he said.
"We prepared for it last night. It wasn't reactive it was proactive...last night worked exceptionally well and it worked against a backdrop of the greatest celebration for British sport that I have witnessed in my life."