By chance, I happened to be in Los Angeles on the day of the big immigration rally. Half a million people marching against a proposed federal crackdown on illegal aliens. Somehow, I managed not to see any of it.

Tell you what I did see, though: both figuratively and literally, signs of change. I grew up in Los Angeles, in South-Central to be exact. Back then it was, or so I once read, the largest black enclave west of the Mississippi.

Not that you’d know it from the aforementioned signs. The churches have become “iglesias.” The markets, “mercados.”

I recall a grand total of two Mexican kids in my high school. Driving by the campus last Friday, I saw “only” Mexican kids. When I was a boy, the mayor of Los Angeles was a white man named Sam Yorty, then a black man named Tom Bradley. Now he is a man named Antonio Villaraigosa.

Over breakfast Saturday, there was grousing from some of my relatives about the influx from Mexico. I pointed out that until 1846, California WAS Mexico. “They’re just taking it back,” I said, “one baby at a time.”

I meant it as a joke, but on reflection, I think it gets to the heart of what has some people scared. In a word, change.

I’m all for immigration reform. Not that I think all reforms are created equal. For instance, some want to build a fence along our border with Mexico, which seems to me impractical and rather draconian. Others, and I count myself among them, favor beefing up the 11,000 person Border Patrol and using high-tech sensors to track illegal crossings. I also support President Bush’s idea for a guest worker program, which strikes me as a pragmatic recognition of an obvious truth: most Americans would rather not pick produce for a living.

All that said, it seems plain that much of what drives the nation’s unease over illegals has little to do with economics or even national security. As columnist Cal Thomas put it recently, Americans fear “invasion without assimilation,” an influx of people who retain their native languages and customs and thus threaten our “unique national identity.”

Put aside for a moment that our “unique national identity” is not nearly as monolithic as he makes it sound, this being a place where one can hear country music, eat paella or gomen watt, worship at synagogue, buy a sari and rent a Gerard Depardieu movie without ever crossing the street.

The larger point is unassailable: the country is changing. I just disagree that change is to be feared. If human history tells us anything, it tells us human beings are not static. Language is fluid, culture shifts and populations move, driven by war and famine, pulled by opportunity and hope.

Yes, it is jarring when you go to places you used to know and find that now everybody habla espanol. But so what? There is a growing population of Muslims in France now, but so what? Traditionally whiter-than-Osmond Minneapolis is absorbing a population of the Hmong people, who hail from Southeast Asia. And so what?

Not to minimize the difficulties these things bring. No, my point is simply that change has been the one constant of history. What made us think our time would be different?

The challenge is not to avoid change, but to manage it, to find ways of living together. It’s a moral obligation, particularly in a country whose founding principle isn’t shared language or shared bloodline but rather, shared creed. Meaning that truth Thomas Jefferson held self-evident.

Put it like this: an influx of people doesn’t threaten our national identity. It IS our national identity.

So there’s something ironic in the idea of Americans standing by the borders wringing their hands over illegal immigrants who don’t assimilate into the local culture.

For what it’s worth, I’m sure the Cherokee once felt the same way.

Leonard Pitts Jr. is a columnist for The Miami Herald. His e-mail address is: lpitts@miamiherald.com.