Kim Clijsters and Justine Henin have come out of retirement. Martina Hingis may be contemplating a third playing career after the end of her drugs suspension. Ana Ivanovic, Dinara Safina and Svetlana Kuznetsova, recent world No 1s, have tumbled down the rankings. Maria Sharapova, at the grand old age of 23, yearns for the injury-free days of six years ago when she won her first Grand Slam title at Wimbledon.
Women's tennis rarely stands still, with one glorious exception. When the players walk on to Wimbledon's Centre Court for the women's final in a fortnight's time, nobody will bat an eyelid if the contenders are two sisters raised in Compton, a Los Angeles suburb with a history of violence and gang disturbances.
Of the 10 Wimbledon finals since the start of the millennium, only one has not featured either Venus or Serena Williams. Venus has won the title five times, two more than her sister, and they have played each other in the final on four occasions.
Venus, 29, won her first Grand Slam title at the All England Club in 2000. The players she beat that year – with the exception of her sister – have all since retired. Serena, 28, won her first Grand Slam title a year earlier at the US Open, where Monica Seles, Lindsay Davenport and Conchita Martinez were among her victims.
In such a physically demanding sport, it is an astonishing record of durability, which shows no sign of ending. Serena and Venus go into Wimbledon, which starts tomorrow, as Nos 1 and 2 in the world respectively for the first time in eight years, their grip on the women's game apparently stronger than ever.
There was a time when the sisters were routinely criticised for failing to treat the women's Sony Ericsson tour with the respect it deserved. It was said that they cared only about the Grand Slam tournaments.
Today such criticisms are rarely heard. Not only is Venus enjoying one of her best years outside the Grand Slam events – she has won two titles, lost in two other finals and never lost before the quarter-finals – but the rest of the world is also finally understanding that one of the major reasons for the sisters' longevity is the fact that they did not burn themselves out when younger.
"There definitely has to be something to it," Venus said. "I think it's been a huge contributing factor to being able to be here and just playing great. A lot of people have followed and have been doing it the classic way, but for Serena and I it's worked."
It is a strategy the sisters have followed ever since their earliest days on the court; their father, Richard Williams, having plotted their careers even before they were born. It was when he heard a TV commentator mention that Virginia Ruzici, the 1978 French Open champion, had earned $40,000 (£27,000) for one week's work – more than he had earned all year from his security business – that Richard told his wife, Oracene: "We need to make two more kids and make them into tennis superstars."
Venus and Serena had rackets in their hands almost as soon as they were strong enough to hold them. Richard took his five daughters every day after school to public courts in a park in Compton. To the occasional sound of gunshots from drive-by shootings, they would do drills and stretching exercises, work on their swing and play points against one another. What they never did, until Venus was nine years old, was play in tournaments.
"The rule was that I could play in a tournament when I beat my father," Venus recalled. "We were out practising in the park one night. We played a match and I got to beat him. He was a good player, but I was strong and tall. I think the score was 6-3. It was only one set. I just remember thinking: 'I'm going to get a chance to play a tournament!' I don't think I actually got to play in a tournament until a year later, but at least I was able to do it.
"The thing is, it's not good anyway for eight-year-olds to be out there playing tennis tournaments so soon in their lives. But when I did get to play in a tournament, when I was nine, I was overjoyed."
Although they played in only a limited number of tournaments, the girls' ability was soon evident. At 14 Venus made her debut on the senior tour, beating Shaun Stafford, the world No 58, in her very first match.
"I don't know what I did to win," she said. "I remember not being nervous. Once I got to the coin toss I felt great. I just hit the ball. I didn't have particular strength or energy, but I had talent."
In the next round Williams seemed to be heading for an astonishing victory over Arantxa Sanchez-Vicario, the world No 2, before losing in three sets. "I was a set and 3-0 up, but then she took a bathroom break," Venus said. "I wasn't smart enough at the time to be able to understand what was going on. There was some gamesmanship there."
Williams, nevertheless, played only nine senior events in three seasons after making her debut. That was down to her father, who has remained the biggest influence on her career. "I'm always on the court with my dad. I'm not training for five hours on the court, because that would be counter-productive to a nice, long career, but I put in the time and it pays off."
She adds: "There are always things to learn, ways to get better, things to pinpoint. The thing about tennis is if you stay off for two weeks, or just for three days, you can lose your rhythm quickly. So it's just a question of constant diligence and vigilance."
The years have brought such a level of self-confidence that Williams is never too concerned about her rivals. "The strategy might change a little bit with each opponent, but I try to think of myself in my own world, my own bubble on my side of the court, and just play the ball," she said. "More and more these days I think less and less about who is across the net.
"If it's a new opponent, I do watch what they're doing. To be honest by the time the warm-up is over, or the first couple of games, I have a really good feel for what is happening."
Sibling rivalry has helped maintain the desire to keep improving. "I think Serena has really pushed me to the next level. She's made me want to achieve more. If I see her doing well I want to do better. If I see her lose I want to do better as well. Either way, I think we've pushed each other. It's a unique thing."
Has the thought of retirement ever entered her head? "Not for a long time yet," she says emphatically. "I love what I do. I'm quite good at it, which makes it a lot easier. I don't think about allowing my hunger to diminish. I'm always trying to take it to the next level. I keep trying continually to improve. The day I'm not improving will be the day I hang up the racket."
Mauresmo doesn't let grass grow under feet
A familiar figure playing an unfamiliar role will be seen on Wimbledon's practice courts this week. Amélie Mauresmo, who retired last year, is helping Michael Llodra, the world No 46 in singles and No 33 in doubles, during the grass-court campaign.
"We've known each other for a long time and we've often talked about his game and his career," Mauresmo said last week in Eastbourne, where Llodra was playing in the Aegon International.
"He asked me if I would be interested in coming over to England with him for the grass-court season, ending up at Wimbledon, and I said yes."
The 2006 Wimbledon champion is working alongside the 30-year-old Frenchman's coach, Rémi Barbarin. "It's going well," she said. "I think I can give Mika the benefit of some of my experience in terms of how to prepare for matches and tournaments."
With a big serve and sound volleys, Llodra should have a good record at Wimbledon, but in nine visits he has won only four matches.
"He has the game to do well on grass, but he's never gone past the second round at Wimbledon," said Mauresmo. "That's obviously quite frustrating for him. He's had tough draws and injuries, but he's also never really believed in his game."
Mauresmo was working for television during the recent French Open, her first such engagement following her retirement. "I enjoyed it, but I'm enjoying this more," she said. "It's more involved and I think I can make better use of my experience.
"When you're commentating, points go quickly, one after another, and you don't have the time to get into any sort of detail. With this role we are working together every day and we have time to sit, to talk, to practise. It's richer.
"I've never worked with another player like this before. I was into my own career, completely focused on that. I'd never really thought about doing anything like this until Mika asked me.
"It's not really coaching. I don't see myself as someone who's going to be a coach every day of the year. I just think I can add some 'extra value' in certain circumstances."
Women coaches are rare at the highest level, especially working with male players. Denis Istomin and Donald Young are both coached by their mothers, as were Marat Safin and Jimmy Connors early in their careers.
Otherwise the most notable player to work with a woman on a long-term basis was the Russian Andrei Chesnokov, who was coached by Tatiana Naumko.
Mauresmo, who was coached by a woman, Alexia Dechaume, in her early twenties, thinks the main reason there are so few female coaches is that women generally want to start families when they finish playing. "In society in general it's fine that the man leaves the house to work, but I think it's a bit more difficult for women to do that," she said.
Might Mauresmo work with Llodra beyond the grass-court season? "I guess we'll talk about it after Wimbledon – about what was good, what wasn't good. But for both of us it's really only about grass at the moment."