Imagine being the last speaker of a language. Dolly Pentreath was a gentle soul who lived in a village improbably called Mousehole in the English county of Cornwall. Although she probably wasn't the last speaker of Cornish, a Celtic language much like Welsh, Dolly came close.

When Pentreath died in 1777, she left behind few who still spoke the old tongue.

Thousands of languages have met the same fate over the centuries. In our time, many African dialects disappear with each new Saharan famine.

Like plant and animal extinctions, language loss is irreparable.

So I'm glad to hear that British Broadcasting Corp., working with songwriter and activist Bob Geldof, is assembling Web materials and a television show aimed at documenting every modern-day culture.

The project aims at producing a record of books, films, photographs and art -- and of course, language -- that will add even the most remote societies to our permanent history. Interestingly, it will include tools to allow people to trace family history.

I have a theory that most of us are historians in one way or another.

Maybe it's history in the broad sense, collecting books about a particular Civil War battle, or maybe it's the more personal gathering of genealogical records. The Web makes both kinds of information-gathering feasible, but it also records a more intimate history, one based, keystroke by keystroke, on the things we look at while we're online.

And that can get scary.

Consider Google's new project, Web History (www.google.com/history).

If you sign up for an account -- and this is the same account you would use for Gmail and other Google services -- you will be able to use the new service, provided you also download the Google Toolbar (toolbar.google.com) and turn on its PageRank feature. Doing that lets you browse anything you have looked at on the Internet, a personal digital history that tracks your search queries, which sites you visited, which files you downloaded and more.

The idea is that the pages you visit comprise a library of information useful to you.

Rather than having to re-create a search every time you want to find something you remember having seen, Web History lets you revisit those sites easily and search the full text of pages you have seen. You also get usage trends showing your surfing habits. Thus Google reminds us that any Internet site can collect usage information, although in most cases we don't think about it.

How all this plays into the hands of advertisers is always an issue, and my guess is that Web History is going to meet with a mixed reaction.

Google has, after all, just completed the purchase of the online advertising company DoubleClick. The $3.1 billion deal further tightens the company's hold on Web advertising and gives it access to DoubleClick's behavior-targeted tools.

I can see an already powerful privacy backlash gaining more momentum.

After all, many users rightly associate DoubleClick with privacy intrusion. The company's cookies are famous for tagging user Web behavior that can later be exploited to serve up targeted ads.

Making ads relevant is a matter of mining gathered information, and Web History points to just how much information Google can gather about its users.

Web History is doubtless a useful tool, but it's not one I intend to activate.

If Web History draws more attention to how advertising dollars are driving the Internet, so much the better.

If this kind of data mining alarms you, ponder a new tool, Evolution.

Created by a South African security researcher, Evolution was designed to highlight not only how much data we put on the Net every day, but how readily it can be exploited.

The software works with multiple search engines and also with social networking sites such as MySpace.com in a quest to link personal data from resources all over the Web. One site leads to another as Evolution tracks e-mail addresses, domain names and more.

We've come a long way from history with a long view -- as in preserving human languages in danger of extinction -- to today's short-term sense of history -- in the trail a person leaves on the Web.

And what stands out is the sense of immediacy that drives today's frantic keyboarding. We're putting vast amounts of information online in a quest of free information or sharing with friends.

In many cases, we don't stop to examine how complete a record this activity is leaving, not only of our thinking, but our daily activities.

No wonder identity theft is the definitive crime of our time.

When a people loses its language, its identity dies slowly. Today, a dedicated hacker can strip the identity of a careless individual out of Web postings, MySpace chatter and a personal history of Web searches.

A virtual identity operating as the original one can not only be created, but after being indexed by the major search engines, can take on a history of its own. That makes history both scary and relevant. What we post on the Web lives and continues to point to us.

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