There are 151 million women in the United States, but only three of them are ranked among the top 68 in the world in women's tennis. So here's the question.

Where would we be without the Williams sisters?

Up the creek without a racket?

The question is timely because come Thursday, Serena and Venus will play separate semifinals at Wimbledon. If they win, there will be an all-American championship final on the day after the Fourth of July. Not to mention all-Williams.

And if that happens, since the sisters are sharing an apartment, what we'll really wonder is how the pre-match breakfast might go Saturday morning.

Said Serena at her Wimbledon news conference, "I'll eat all the Wheaties."

The Williams' saga has always been beguiling, except for the occasional verbal double fault by father Richard, who tends to look best when he lets his daughters' tennis do the talking.

But in sizing up this latest sibling collision course, a rather jarring fact comes to mind.

The Williams girls aren't girls anymore. Venus just turned 28. Serena is 26. That is getting on, in women's tennis. "Time flies, you know," Serena said.

It was eight years ago — a tennis eon — that Venus won her first Wimbledon as a powerful 20-year-old, to have her picture included on the wall at the All England Club. Now she looks at that picture and says, "I'm not sure what that girl in 2000 was thinking."

She does remember reading Harry Potter books when rolling to her first Wimbledon. But then, she still reads them. "So not much has changed."

Curious thing about the years since. The specter of parents carting their kids off to weekend tournaments and clinics supposedly helped sell an entire generation of mini-vans. What it has not done yet is fill the upper world rankings of the sport with sons or daughters of an American revolution.

If only three U.S. women in the current top 68 seems meager — Serena at No. 6, Venus at 7, Lindsay Davenport at 25, the trio surrounded by a platoon of Russians — the men fare little better. Five in the top 59. They disappeared from the most recent Wimbledon nearly as quickly as a bowl of strawberries and cream.

It would appear, watching the majors on television, that the rest of the world produces most of the tennis contenders and we produce most of the tennis commentators. Given the history and sheer numbers of players in this country, you'd think it'd be different.

None of that will matter Thursday, however, when the Williams sisters go to work, with six of the past eight Wimbledon titles between them. Neither has lost a set yet in this year's proceedings.

Serena was asked at a news conference if she considered defending champion Venus as the favorite.

"I would never sit here and say she's the favorite when I'm still in the draw," she answered. "What are you on?"

They hope to meet so they can decide not only the best grass player in the world, but also the best grass player in the family. Without such intrigue, the biggest tennis headline of the fortnight for an American woman would have been Chris Evert marrying Greg Norman.

It is hard to think of any other sport where siblings go eyeball-to-eyeball for such a prize. Imagine the hype if it was ever Peyton vs. Eli in an all-Manning Super Bowl.

They have played in the final of six grand slam tournaments. Serena won five. So nothing new, should they meet.

But passing years have a way of making us appreciate something special, such as a rivalry between close sisters with similar genes but different demeanor and style.

Plus, it would remind us of the lean state of American tennis.

If not them, who?