I’ve often wondered what Mary Shelley’s “Frankenstein” would have been like if it had been rewritten by Charles Darwin and turned into a movie by David Cronenberg. Now I do not have to wonder! It would probably be a lot like “Splice,” a delightfully twisted horror thriller from Vincenzo Natali, director of 1997’s sci-fi nightmare “Cube.”

Adrien Brody and Sarah Polley play Clive and Elsa, brilliant biochemists who have led the way in creating a new organism culled from the DNA of several existing species. This new animal produces nutrients that can be used to treat illnesses in livestock; if some human DNA were thrown into the mix, perhaps the resultant creature’s proteins could cure human diseases.

But it would be illegal, not to mention unethical, to use human DNA in this fashion. That is why Clive and Elsa — who are partners in romance as well as in the lab — do it secretly. “What’s the worst that could happen?” Elsa asks, practically daring us to tell her.

Sure enough, a new organism is produced, one with human and animal characteristics. It ages rapidly, allowing a horrified yet curious Clive and Elsa to learn about its entire life span. Oh, and “it” is actually a “she.” The monster baby has a gender. Elsa, who has never wanted to have a real child the normal way, treats this lab-manufactured aberration first as a pet and then almost as a daughter.

Part of the fun in a film like this is seeing what the characters do not see, i.e., that this cannot possibly end well for them. What they’re doing is outrageously stupid — but that’s OK, because we enjoy seeing what happens next. Like the ambitious but misguided scientists in the monster movies of yesteryear, Clive and Elsa have tampered in God’s domain, and for this there must be consequences.

I cannot begin to describe the creepy, giddy, squirm-inducing madness that Natali has conceived with co-screenwriters Antoinette Terry Bryant and Doug Taylor. There are certain things you would expect in a story like this, and most of those happen. But then there are other developments that I’m pleased to say my imagination is not demented enough to have conceived. (There is also an unfortunate tangent about Elsa’s unhappy childhood, which adds nothing and is under-explored.)

Through it all Natali maintains a gleeful tone, clearly enjoying the experience of telling a story that gets crazier and crazier as it goes. Even as events become more shocking, there’s the sense that that’s the point — that by defying the laws of nature from the very start, Clive and Elsa have put themselves outside the normal bounds of what’s “taboo.” In a world like that, no plot device is too grotesque. As viewers, we just have to embrace the insanity and enjoy the wild ride.

B+ (1 hr., 40 min.; R, some harsh profanity, some strong sexuality, some nudity, some intense violence.)