And so the experiment continues.

The Arizona Diamondbacks, quite possibly the oldest team in the history of professional baseball, and perhaps in the history of professional sports, made a big move yesterday to get ... older. They signed Luis Gonzalez to a three-year contract extension through 2006.

In 2006, the Diamondbacks will pay Gonzalez $11.5 million.

Also in 2006, Gonzalez will turn 39 years old.

	Luis Gonzalez hit a combined 85 home runs over the past two seasons.

Make no mistake, Gonzalez is a fine player. His Win Shares over the last five seasons:

      Age  Win Shares
1998   30      12
1999   31      26
2000   32      27
2001   33      37
2002   34      26

There are all sorts of interesting things about Gonzalez's career path. It's not shown here, but Gonzalez also totaled 12 Win Shares in 1997, which is to say that his career was, by the conclusion of the 1998 season, following a typical path. He'd been a pretty good player in his middle and late 20s, but it looked like his best days were behind him. Like so many players before.

As it turned out, though, his best days were ahead of him. You saw the Win Shares already. Here are Gonzalez's key percentages before and after becoming a Snake:

Ages    OBP  Slug
23-30  .341  .432 
31-34  .406  .572

Friends, that's just not something you see too often. But Gonzalez has clearly established a level of performance; the last four seasons include three excellent seasons and one MVP-quality season. So it's not much of a stretch to suggest that Gonzalez will remain an excellent player in 2003.

But 2006?

That's where the experiment gets put to the true test. The great majority of players decline as they enter, and then progress through, their late 30s (he wrote, hoping the same isn't true of baseball columnists). If Gonzalez follows that pattern, by 2006 he'll be one of the most overpaid players in the game.

But of course, to this point Gonzalez hasn't followed anything like a normal pattern, which is, presumably, why the Diamondbacks made such a large investment in his future.

And the experiment probably won't end with Gonzalez, because the Diamondbacks have a pitcher named Randy Johnson whose contract expires at the conclusion of this season. This Johnson fellow turns 40 in September (his birthday comes a week after Gonzalez's), but if he's anywhere near the end of the line, you sure can't see it on the field or in the numbers.

So what do the Diamondbacks do with this modern Methuselah? If the franchise's history is any guide, they'll make every effort to retain Johnson's services. Unfortunately, history provides little guide to those trying to forecast Johnson's future, because he's pretty close to the first of his kind. Sure, Nolan Ryan was still throwing heat when he was 40, but Ryan was far from the best pitcher in his league. Johnson has now won four straight Cy Young Awards, and he's led the National League in strikeouts all four seasons.

In fact, it's these two guys -- Gonzalez and Johnson -- who explain the success of the Diamondbacks. Both joined the franchise in 1999, and since then both have been outstanding while making a mockery of "typical" career paths. Meanwhile, the Diamondbacks have reached the postseason three times in those four seasons.

Have the Diamondbacks been lucky? Or did GM Joe Garagiola Jr. spot something special in Gonzalez and Johnson?

Should we throw out everything we know about the aging patterns of baseball players? After all, Barry Bonds doesn't seem to be suffering any ill effects, either. Not long ago, I asked Bill James about this. He'd recently done a comprehensive study of aging patterns, and found not much of anything. Players typically peak in their late 20s before beginning the slow decline that eventually results in forced retirement. Still.

Then again, it's possible that something's changed so recently that it doesn't show up in a comprehensive study. It's possible that Randy Johnson will continue to pitch brilliantly for another two or three years, and it's possible that Luis Gonzalez will be just as good at 38 as he was at 34.

The Diamondbacks seem to be banking on this theoretical change. Not only with Gonzalez and Johnson, but also with Steve Finley (who will be 39 when his contract expires next year) and Mark Grace (who turns 39 this June).

And if they're wrong? The D-Backs could be in for a rough year or two. Fortunately, the farm system is pretty stacked with solid prospects, so if the organization isn't financially crippled by long-term contracts, the future actually looks pretty bright.

In 2003, though, the future is now. The Diamondbacks will go exactly as far as their old men can take them.

Senior writer Rob Neyer, whose Big Book of Baseball Lineups will be published in April by Fireside, appears here regularly during the season. His e-mail address is rob.neyer@dig.com.