In X-Men: First Class, the latest film about the popular comic book superheroes, one of the mutant characters goes by the nickname Darwin because he has the power of "reactive evolution." He instantly adapts to any threat: toss him in water and he sprouts gills; hit him with a club and his skin turns to armored plates.

Biology mavens in the audience may object that this form of evolution is more or less the opposite of what Charles Darwin proposed with his theory of natural selection. If anything, the mutant’s abilities are more in line with the rival, disproved theories of Jean-Baptiste Lamarck, who argued for the heritability of acquired characteristics. But maybe the name "Lamarck" would sound too much like a maitre d' rather than a mutant to fans.

That misappropriation of Darwin’s identity is emblematic of the X-Men films’ tortured portrayals of key ideas in biology. The movies are of course meant to be fun, not factual, and it feels like the height of stodginess to warn: “SPOILER ALERT: This film about superpowered telepaths and shape-shifting blue women is not a science documentary." There’s probably no point in wasting time discussing how various powers conferred by the fictional X-gene mutations violate physical laws, because they are really fantasy devices like the spells in Harry Potter books.

Nevertheless, it is worth looking at some of the film’s errors about evolution and speciation because they may be reinforcing some popular misconceptions.

X-Men: First Class, like earlier movies in the series, repeatedly invokes the idea that its mutants and humans are engaged in an evolutionary struggle for dominance like the one between humans and Neandertals thousands of years ago. Professor Xavier and Magneto talk about the Neandertals having resentfully looked at the superior new species moving in, and the moderns having displaced and slaughtered the older species.

At least this movie has the excuse of being set in 1962, when such ideas about human evolution were more common. Neandertals were then typically portrayed as a species of mentally inferior brutes who could not compete with the smarter, more technologically and culturally advanced Homo sapiens who evolved later.

But today, the paleoanthropological picture of the relations between Neandertals and modern humans is completely different. Skeletal reconstructions show that Neandertals had brains larger than our own, and archaeological digs reveal that they had a distinct culture but sometimes used some of the same tools that our ancestors did. Indeed, studies published in 2010 by Svante Pääbo's group at the Max Planck Institute for Evolutionary Anthropology in Leipzig concluded that several percent of non-African people’s genes came from Neandertals, so Neandertals may not even have been a species apart.

Most important, little evidence supports the idea that Neandertals and modern humans were in much open conflict. During the last ice age, Neandertals may simply have fared poorly and gone extinct largely on their own, with modern humans later occupying their old territories and perhaps breeding with some stragglers. One recent controversial study has even suggested that Neandertals were essentially gone from Europe by 40,000 years ago, thousands of years before modern humans arrived. In any case, Professor X and Magneto had it wrong.

Beyond the particulars of Neandertals and modern humans, though, X-Men’s abundant speeches about the "next step in human evolution" only make sense if evolution is seen as the gradual realization of some design embedded in nature. Accordingly, the emergence of superior new species—not just new species in general but particular, better species—is supposed to happen, and woe betide the older ones that stand in the way of that progress.

Current conceptions of evolution reject those views, however. Smart evolutionary biologists avoid referring to hierarchies of species in which, say, apes count as higher organisms and snakes as lower ones. Species are understood to emerge only if environmental conditions allow new, distinct breeding populations to branch away from their predecessors. The prospects for new species to survive or replace ancestral ones are equally hit or miss.

Mutants in the X-Men films are always treated as a distinct species, but most of them can apparently pass as human and spawn children with them. Those facts do not absolutely eliminate the possibility that the mutants are a different species (because related species do sometimes limitedly crossbreed in nature and bear fertile offspring, as wolves and coyotes have). Yet it also isn't clear that the mutants would preferentially breed among themselves, as a species must under at least one widely-known biological conception of a species.

Recognizable species also usually have a definable phenotype, or set of characteristic physical features. The X-Men mutants, in contrast, are a crazily diverse mélange of types (teleports! banshees! living ray guns!) who are on average at least as different from one another as they are from the rest of humanity.

So contrary to the film’s heroes and villains, X-Men mutants are not innately a new species, just another variant of Homo sapiens. They cannot become a new species (or more than one) unless geophysical or other circumstances create an irrevocable barrier to their breeding with the rest of humanity. Tolerance of one another’s differences could be enough to prevent that outcome. So in that sense, notwithstanding the dodgy science along the way, the film's underlying message is probably right after all.