It was in the 19th century that scientists realized the ridged whorls on the tip of the finger constituted a unique marker that could be used to tell one person from another. And eventually, the FBI built a massive database of fingerprints.

Then came DNA. In the 20th century, scientists learned to use the double helix nucleic acid molecule as a means of identification even more definitive than the fingerprint. And the FBI built a DNA database as well. Now the feds are building yet another database. And it has some folks worried.

Maybe you missed it in the run-up to Super Duper Tuesday when the Associated Press reported last week that the FBI will soon award a $1 billion, 10-year contract for construction of an electronic file that would store not just fingerprints and DNA, but a vast compendium of other physical characteristics. We're talking eye scans, facial shape, palm prints, scars, tattoos and other biometrics, all for the purpose of identifying and capturing bad guys.

But at least one privacy advocate thinks even good guys — and gals — have cause for concern. Barry Steinhardt, director of the ACLU's Technology and Liberty Project, told CNN, "It's the beginning of the surveillance society where you can be tracked anywhere, any time and all your movements, and eventually all your activities will be tracked and noted and correlated."

I know what some of you are saying and it makes a certain amount of sense: If you haven't done anything wrong, you have nothing to worry about. Well, I haven't done wrong, but it worries me just the same.

The government has for years collected fingerprints — not just of criminals, but also of certain job applicants. What's happening now, it could be reasonably argued, is only a high-tech extension of that. Except that instead of just your fingerprints, the government will also have on file the shape of your iris, that scar from your appendectomy and the tattoo on your inner thigh.

It's a discomfiting reminder of the totalitarian states of "Fahrenheit 451" and "1984," oppressive regimes that saw everything, knew everything, regulated everything. Given the advances in technology and the ominous, Orwellian turn our government has lately taken, the comparison seems far less far-fetched than once it might have.

It's not just the government, though. In recent years, the right to privacy, the right to simply be left alone, has also been eroded by the corporate community — everything from supermarket discount cards that track your buying habits to online businesses that install secret spyware in your computer. And we haven't even mentioned that there is a camera on every street corner nowadays.

"I always feel like somebody's watching me." That used to be just the hook from a schlocky '80s song. Increasingly, it is an apt description of modern life.

Now the FBI proposes to collect and collate still more personal information. It swears the information will be protected, and will be used only to ferret out criminals.

But I can't help a certain wariness when I consider the ease with which the program could expand far beyond that mission. As Steinhardt sees it, first criminals, then job applicants and then, "Eventually, it's going to be everybody."

I admit, he might be wrong. But you know something? He might not.

Leonard Pitts Jr. is a syndicated writer in Washington.