How do we account, “Splice” asks, for the kindred dorkdom of lab-cloistered scientists and monster-movie completists? Are we talking nature or nurture here?

Adrien Brody and Sarah Polley are Clive and Elsa, two fetching young geneticists whose romantic forays into bioengineering go about as well as you’d expect from a movie that names its characters after actors in “Bride of Frankenstein.” Which isn’t to say that director Vincenzo Natali and his co-writers Antoinette Terry Bryant and Doug Taylor are especially old-fashioned. Rather, they seem a little desperate for edgy topicality. It’s just that they’re also preoccupied with matters of heritage.

After combining the DNA of various animals into a pair of enormous, pharmacologically useful slugs, Clive and Elsa now are eager to see what they might whip up by throwing some human genes into the mix. Their corporate overseers seem less keen on the idea, and you would too after the doozie of a scene in which a demonstration goes just wrong enough to shower the shareholders with glass and blood.

But Clive and Elsa are ambitious. And they seem to understand each other. “I am not spending the next five years digging through pig shit for enteric proteins,” she tells him. “Me neither,” he says. And their haste is contagious: Natali flips on the scientists-at-work montage, and before we or they know it, Clive and Elsa have become the proud yet also ashamed parents of a little baby rodent-bird-amphibian-arthropod girl.

OK, so this is sort of a weird situation, but apparently it’s still better than the pigshit. They call her “Dren,” because that’s “nerd” spelled backward and their lab is called Nucleic Exchange Research and Development. They determine that she “craves high-sucrose foodstuffs,” which seems normal enough, and that she “develops like a fetus outside the womb,” which seems less normal, but does at least present some invigorating challenges, both personal and scientific. (Not to mention cinematic: Natali marshals Howard Berger’s excellent special effects with discretion enough to allow for an actual performance as the developing Dren by young Abigail Chu.) Then, needing some privacy to fully slough off the pretense of professional principles and delve into their respective parent issues, they spirit her away to Elsa’s conveniently long-abandoned family farm, way out in the gloomy woods.

Kids grow up so fast, don’t they? Especially when the movie needs them to. Sooner than soon enough, Dren has developed to the point of being played as a nominal adult by the model Delphine Chanéac — all ornery, attention-wanting, bald and sexy, like Sinead O’Connor but with a tail and kangaroo legs. For review purposes, details hereafter are best left vague.

Suffice to say there’s a lot going on in “Splice.” It’s not quite the subversive cult-movie romp it might have been, but transgenderism, incest and bestiality all at once has to count for something. And Brody and Polley remain impressively undaunted by all the confused instincts, Freudian eruptions and other karmic consequences that Natali and company manage to hurl at them. Still, leaving no trope unturned means not giving any enough consideration. In its final act, “Splice” seems to have hemorrhaged all inspiration, and finally just trudges to an obligatory bore of an action climax. Of course this might be par for the course of a movie whose point, at least in part, is: “Well, that wasn’t a very good idea.”

Unless maybe, God forbid, it was. Which would go to show: Whether you’re working with strands of DNA or with strips of film, the power of the splice is its creative potential. You just have to keep an open mind. Tell yourself there are no mistakes, only choices. No abominations, only fascinations. And while you’re at it, tell yourself that a lot of life’s mystery is explainable, as the fertile combination of mad science and bad parenting.