Last summer, “Prometheus,” the long-anticipated prequel to the “Alien” franchise, was marketed as a thought-provoking science fiction film. What we got was a classic sci-fi trope with some added references to actual scientific concepts, though some of them bordered more on pseudoscience and conspiracy theory than actual science.

The film’s main premise — that extraterrestrial visitors began life on the Earth — is actually quite an old one. Many sci-fi films have used it, and in real-world speculation it is known as the Ancient Astronaut Theory. It’s a less-than-credible theory; there is no evidence for it apart from Mayan paintings of visitors from the sky and a sneaking suspicion that pyramids could not have been built without advanced technology. It’s really more of a conspiracy theory, a way of avoiding the question of life’s origin by saying it must have been aliens.

The film tries to legitimize the Ancient Astronaut Theory by relating it to real science about evolution. A study of the film reveals a less-than-thorough understanding of how evolution actually works. In the opening scene, an alien drinks a substance that causes his body to disintegrate and fall apart into a stream, where his DNA begins restructuring itself into the building blocks of life. Millennia later, the film’s scientist characters stumble upon the aliens’ home world, where they discover that their DNA is identical, indicating that the aliens are their creators.

This is a classic misconception about evolution known as the teleological view. Teleology is the uniquely human practice of assuming that things occur with purpose. It is a logical fallacy of attributing human forethought to events in nature that occur with no forethought or purpose. A single-celled organism is not “working toward” any ultimate result by evolving; it is not destined to accomplish a goal of evolving into a human. It is responding to changes in its environment that push it in one evolutionary direction or another. If aliens really dumped raw genetic material into a stream, they would have no way of assuring it would evolve into anything remotely like them. Even if they had some means of controlling the development of subsequent genes, it could not explain the huge variety of nonhuman life that evolved from the same source. Furthermore, raw, broken genetic material from a dead organism may not be equipped to evolve into anything.

Despite this, there is one aspect of evolutionary biology the film got right: The “Alien” predecessors Facehugger and Xenomorph actually answer some biological mysteries about the original film’s creatures near the end of the film. The Facehugger in the original “Alien” is a creature that can reproduce with any other animal, thus producing a hybrid organism (the Xenomorph) capable of living in that animal’s environment. In the first “Alien,” a Facehugger reproduces with a human, leading to a bipedal Xenomorph that breathes oxygen and can live on a human spaceship. However, the Facehugger seems perfectly designed to fit around a human head. It would work with nothing bigger, or with a wider neck or a longer snout. So, its usefulness as a universal parasite is minimal. It must have evolved a specialization to the human face through exposure to humanoid DNA over time.

Prometheus shows the original Facehugger: A larger, more powerful, more flexible parasite that can work with anything. Over several generations when the only DNA it could co-opt was humanoid, it would evolve into the humanoid specialization we see in “Alien.” Similarly, the Xenomorph we see at the end of the film is a logical ancestor to the one in “Alien.” The elongated head is a bladed appendage for escaping the host, not unlike a snake’s egg-breaking tooth. Over time, the blade becomes unnecessary as the creature evolves to be smaller at birth, punching its way out of the host instead. The elongated skull becomes more rounded to accommodate a larger brain inherited from human DNA, much in the way evolution in the real world modifies existing appendages for alternative use. So we can at least say the creature designers for this film, if not the writer and director, understood a few things about evolution.

A version of this article appeared on page 5 of January 29th, 2013’s print edition of the Nexus.