Art is an evolutionary process – you adapt or perish.When the photographer made his hesitant entrance at the beginning of the 19th century, painters and sculptors paid scant attention. The newcomer then stole much of their territory.

By the end of the century, however, artists had reasserted themselves by discovering impressionism, expressionism and all those other isms.

The advent of motion pictures put the theater in a similar position, as there became many things that were done better on film and TV than on stage.

But just as the painters found a fresh way of distinguishing themselves, so, too, did 20th-century playwrights, from Pirandello to Brecht, from Williams to Miller.

Three recent plays – Tom Stoppard’s “The Invention of Love,” Simon McBurney’s “Mnemonics” and Peter Nichols’ “Passion Play” – offer wonderful reminders of the distinctive appeal of staged drama.

“Invention,” a fragmented portrait of A.E. Housman, is an example of how Stoppard writes comedies of suggestion rather than statement. Here we have the making of a scholar, but also the unmaking of a man.

Here also is a new and gilded aestheticism – a civilization moving into the 20th century’s more permissive approach to Eros and to life itself, typified by Oscar Wilde’s Dionysus opposed to Housman’s Apollo.

And it is a play that, because of its many layers of feeling and even action, could not be anything but a play.

With “Mnemonic,” described as being “devised” by the dazzling British troupe with the funny French name, Theatre de Complicite, you have something that is hardly a play at all, but an intense theater experience.

In at least three interlinking stories – two contemporary and one concerned with that celebrated 5,000-year-old Ice Man left fossilized in the Alps – the play wondrously develops themes of memory, fate and inheritance as it considers the family of man.

“Mnemonic” cannot be forgotten. I promise you it will be a marker in your theater-going experience, perhaps even your life.

“Passion Play” is the most conventional of this terrific trio, but like the other two, it is beautifully written, staged and acted.

It is a play about adultery and its effect on a happily married couple with many years of physical desire and fidelity behind them.

The special device here is to give both husband and wife an alter superego, advising, commenting and sometimes confusing.

When “Passion Play” was first given in London and New York, it suffered from coming at the much the same time as Stoppard’s own play about adultery, “The Real Thing,” but it is a superb and unexpectedly moving comedy of manners in its own right.

People always claim that the great advantage of the live theater is that it offers the immediacy of real-life actors on a real-life stage.

True, but it also helps if the play offers a special insight and technique that cannot be decently duplicated by either movies or television.

These three plays all do just that. Give ’em three cheers!