Evolution is a 2001 American science fiction comedy film directed by Ivan Reitman and starring David Duchovny, Orlando Jones, Seann William Scott, Julianne Moore and Ted Levine. In the United States, it was released by DreamWorks and internationally, by Columbia Pictures.
A short-lived animated series, Alienators: Evolution Continues, that was loosely based on the film, was broadcast 3 months after the movie was released.
Wayne Grey (Seann William Scott) is practicing a fireman rescue in the desert outside the sleepy town of Glen Canyon. However, before he can enjoy his victory of a successful practice and good timing, a meteor falls out of the night sky and plummets into the ground, causing his car to fly into the air and crash down, severely damaged. Elsewhere, the next day, Community college professor, Ira Kane (David Duchovny) has just dealt with the idiots of his class - the Donald brothers Deke (Ethan Suplee) and Danny (Michael Ray Bower) - and is taken by his friend, geology teacher/girls' volleyball coach Harry Block (Orlando Jones) to investigate the meteor as part of his job as a member of the U.S.G.S. (which he signed up for by accident).
They meet Wayne and the police who have been questioning him all night, learning that the meteor fell through the ground and into a network of underground tunnels. After informing the police of their authority, Ira and Harry take a sample of the meteor, only to find, much to their bewilderment, that it bleeds out blue liquid. While Harry coaches a volleyball game, Ira investigates a sample of the blue liquid to find single-celled nitrogen-based organisms that multiply quickly, leading Ira to conclude that these organisms are extraterrestrial. Bringing Harry back from the game to see the aliens in person, Ira is shocked to find that they have evolved in multi-cellular organisms by the time they return. Ira is truly shocked by this, but Harry can only think about how this discovery may win them a Nobel Peace Prize.
Impressed, the two take the science class to survey the meteor site the next day, planning to retrieve the meteor for their own tests under the guise of their being under orders from the U.S.G.S. However, much to their surprise, the ooze from the meteor has rapidly evolved into oxygen-converting fungi and alien flatworms that thrive in the converted atmosphere. Unable to retrieve the meteor now, they take some flatworms back with them in a container and learn that they reproduce through mitosis (splitting apart). Harry thinks they should involve the government with this, but Ira thinks different; he believes that since they discovered the aliens, they should be the ones to do the testing. In the meantime, Wayne, who works at the country club, finds some dead flatworms appearing near the water heater room while retrieving a fresh towel for annoying patron Barry Cartwight; trying to poison the flatworms, Wayne is scared off by a reptile-like alien that evolved from a flatworm that got into the water tank.
The next day, Ira and Harry find that their specimens have multiplied into three different sub-species, wondering what they will find at the meteor site now. However, upon arrival, they find that the army has begun setting up a base, much to their annoyance. When Ira asks a guard to inform his superior of his and Harry's connection to the site, another soldier tries to point a gun at him because of something Ira did in the past, but is quickly detained by other soldiers; Harry wonders what Ira did, but he remains mum about it. Allowed in, they meet General Russell Woodman (Ted Levine), head of army research who worked with Ira in the past. Woodman reveals that they have been hacking into Ira's computer to keep and eye on him and his activities, much to Harry's shock because of some pictures he had on it. They meet klutzy Dr Allison Reed (Julianne Moore), head of epidemiology at the C.D.C., who views Ira's actions as dangerous, but promises to keep him and Harry informed of the research they will do with the aliens. Annoyed, Harry and Ira drive away, promising they will get back at them, while Ira moons Woodman in revenge.
Around two weeks later, Harry and Ira have taken Woodman and Reed to court for the right to be part of the alien research, but Woodman has an ace up his sleeve to make Ira look incompetent as a scientist; five years ago, he was discharged from the army because of an anti-anthrax drug he created and tested on soldiers resulted in a long list of terrible physical and mental disorders called the 'Kane Madness'. The judge rules in favor of the military and forbids Ira and Harry from approaching the base. Heading back to their lab, Harry tries to cheer Ira up by informing him that Dr. Reed likes him, but Ira once again thinks otherwise. However, upon reaching their lab, they find Woodman has had it cleaned of all their samples and research files on the aliens, much to their growing anger. Harry wishes to call the police, but Ira point out that they ARE the police; Harry wonder what to do.
That night, Ira dresses in his old uniform and Harry dresses as a private, allowing them entrance to the lab. Acquiring protection suits, they head underground to get another sample of the meteor and a specimen, finding that the fungi has evolved into a rain forest and the creatures have reached the size of pets; some of the plants are alive and carnivorous. Failing to catch a specimen out of Harry's fear of dying due to movies he has seen and other creatures eating smaller ones, Harry notices an alien with a large behind after seeing an alien with a head on the front and the back of it is eaten by it. Harry once again tells Ira that Dr. Reed has a thing for him. Above, Dr. Reed and the others have noticed Ira and Harry, overhearing their conversation. Ira believes Dr. Reed has no human emotions what-so-ever, being an "ice queen". However, Harry thinks she just acts like that as a cover and just needs some good sex. Annoyed, Ira reminds him the purpose of why they're there and they head to collect a meteor sample. However, Dr. Reed, Flemming, and another soldier arrive and catch them. Dr. Reed explains that she did not take their notes and specimens after Ira accuses her and begins questioning the others if THEY did. Their conversation is cut short when an alien fly manages to get into Harry's suit and then inside him. They take him to the surgical wing of the lab and begin wondering how to remove it. A doctor decides to rectally remove the fly, much to the pain of Harry, who, once the fly is removed and then dies within a few moments, tries to strangle the doctor. However, Allison and Ira hold him down and calm him. Harry asks for an ice cream, but instead of eating it, he wants to use it to sooth the pain in his behind.
Elsewhere that night, Wayne is working at the country club, where he has become extremely annoyed with the ridiculous things they have him due for a paycheck. In the meantime, Barry Cartwight is preparing a picnic for his date on the golf course by a pond, only to be attacked by an amphibious alien and dragged into the water where he is eaten. His date (who saw the attack but did nothing to help) runs into the main hall and screams that Barry is dead. Wayne is quite pleased by this news, but masks this the best he can.
In the meantime, Allison is questioning Ira about his past and wonders why he is taking such extreme measures. Ira explains that he has been EXILED in Arizona for five years; the meteor was his most likely chance of getting a good reputation and a way out of Glen Canyon. Allison reveals that she heard everything Ira (and Harry) said about her (how she says it is different, possibly meaning what she actual thinks of herself), telling Ira that he doesn't know about her. Pleased that Allison is not the cold-hearted person he thought she was, Ira thanks her for not arresting them.
The next morning, Ira and Harry (still in pain) return to Ira's office to find Wayne waiting for them. He has with him the (now dead) amphibian alien, having watched it choke to death the previous night with a mob. Both Ira and Harry are shocked by this, believing the aliens are crawling out of the caves and trying to adapt to their environment.
Elsewhere, some women have found a reptilian pug-like alien in a closet, believing it to be a scared dog. However, after it uses an inner mouth to bite one of them, they call 911 while one of them grabs a hidden gun from a drawer. Before a shot can be fired, the alien dies and comically deflates, with the women wondering what the hell it is.
At a hotel, Ira has caught up to a tired Allison and informs her of the aliens spreading. However, she is confident that they can handle the outbreak. Ira warns her pride like that was HIS undoing and convinces her to ask Woodman to find a way to kill the aliens. As a bonus question, Ira wonders if Allison is attracted to him, but gets a "Bye Ira" in response as she leaves. Ira takes this as a "yes" while Allison can be seen with a smile.
At a restaurant, Wayne and Harry having breakfast; Wayne wonders if Harry sees the girl's volleyball team shower and, much to his shock, finds Harry does and sometimes showers with them. Ira arrives and informs them that Allison has been won over and will talk to Woodman about killing the aliens. Much to Ira's surprise he finds his ex-wife at the table next to him with the officer he first met at the meteor site, almost tricking her into taking off her shirt (stolen from him). They overhear the officer get a call about an animal attack and head out after him.
They arrive soon after at the house the alien dog attacked. They check the inside of the house while Wayne does a parameter check. They find the alien crawled through the dirt with flatworms. Wayne enters and tells them there is something they have to see. He takes them to the ledge, where they find several dragon-like aliens (some dead or dying). Climbing down, Harry realizes that the aliens have been using the network of tunnels under Glen Canyon to get around, much to the surprise to Ira. To their shock, one of the still breathing aliens barfs out a pod before dying; it hatches into a yellow dragon alien that is tolerant to Oxygen. It flies away, much to Ira's horror as they chase after it.
They follow it to a mall, where it wreaks havoc and captures a girl attempting to shoplift after hearing her singing in the changing room (apparently hating music). They "commandeer" some guns in the store and chase after it. However, the crowd causes them to lose sight of it. Ira and Harry are prepared to leave and give up, but Wayne tries bird calls, much to their failure and Harry's annoyance. Wayne then begins singing, which draws the alien back to them. Ira gives a single shot that puts the bird down while Harry rescues the shoplifter, who promises not to shoplift again. Ira, Wayne and Harry go over to the alien and joke about carving it like a turkey as it regains consciousness. Each fires a shot, killing it. They leave the mall and sing along with the radio as they head back to the research lab.
In the meantime, other incidents (along with the dead dragon aliens) began happening through Glen Canyon, catching the attention of the media. Wind of this gets to the Arizona Governor, Lewis (Dan Aykroyd), who is airlifted to the base, where he chews out Woodman and the staff for keeping aliens secret from him. Allison then explains that they are in serious trouble now, because if they allow the alien ecosystem to grow, in two months, it will cover the United States. Lewis is shocked, wondering if it is a bad joke. Ira, Harry and Wayne enter and Woodman tries to place blame of the alien outbreak on them. However, Lewis cares less about Woodman's lies and wonders what he is going to do about it.
Woodman explains his plan to evacuate everyone from five miles of the infected area and "bomb the alien menace right the hell out of there" with napalm. However, their attention is diverted from the plan to several cameras being destroyed by the aliens, which have no evolved into primates. They find they have broken through the air-lock and are using elevator. However, when it comes up, it is empty. The lights go out and the alien apes bursts through the tarp over the impact hole, taking the most cowardly soldier back down with them as Wayne shoots the last one, saving the governor and Ira. Scared, Lewis gives Woodman permission to go as far as he needs to get rid of the aliens; Woodman promises to be ready by noon the next day to burn the aliens. He has Ira, Harry and Wayne removed from the base and tells Allison that she needs to be working. Fed up with Woodman, Allison leaves with the stolen research material taken from Ira, joining him, Harry and Wayne on their trip back to the college.
On the trip through the town, the find the number of people being evacuated ridiculous, coming to the conclusion that "they're gonna blow up the whole town". They arrive at the college to find most of the students drunk and dancing while police order them to leave; others are just panicking at the thought of aliens. Inside the lab, Ira tries to talk with the ooze to get an answer on what it's weakness is, only to be met with stares of disbelief. Harry accidentally tosses a match into it, causing a shapeless red mass to grow from the ooze. They all realize that heat triggers the aliens evolution; Wayne advises Allison to call Woodman. However, Woodman is still mad with Allison and refuses the call. Deke and Danny arrive, giving the four some beer to help them relax as Ira notices the periodic table on Allison's shirt, coming up with an idea. Selenium might be poisonous to the aliens as they are nitrogen-based just like arsenic is poisonous to carbon-based life-forms, based on their similar positions in relation to each other on the periodic table. Realizing it would be almost impossible to find 5000 gallons of selenium at 2 o'clock in the morning, Ira is shocked and surprised when Deke and Danny recall that "selenium sulfide" is the active ingredient in Head & Shoulders dandruff shampoo, prompting Ira to award them both A grades in his class, much to the brothers' excitement.
As everyone else is pouring as much Head & Shoulders shampoo as possible in a firetruck, Allison tells Ira she would have rocked his world, to which he tells her she already has. The truck filled to the max, the team takes of, only to find too many soldiers around the main cavern. Harry tells them they can gain access from an abandoned silver mine, which they soon arrive at. Once through, Ira sends Wayne up to the truck to pump the selenium through. Above, Woodman is informed that they can blow up the aliens early and is under threat of the governor to be demoted if he screws up and begins the festivities. Inside the cave, Team Ira is forced to flee outside as the aliens are swallowed by a large red mass that becomes an enormous amoeba by melding together into a single entity. After it surfaces, the amoeba slowly begins mitosis and is found to be invulnerable to conventional weapons; it will continue growing and dividing until it covers Earth.
Wayne wonders if they still plan to use the selenium and this prompts everyone to go for an "all of nothing" attempt as they begin heading to the creature, passing fleeing soldiers. Looking for a point of attack, they find a rectum, which is the only vulnerable part of the giant. Harry goes up the ladder (intending to settle the score with the alien fly from earlier) and shoots the dandruff shampoo into it, causing the mitosis to stop and the creature to begin sagging, causing Harry to be half-way swallowed into it. Ira rescues him as the creature begins swelling. They manage to leave before the creature explodes into a rain of lime goo. Perhaps as an act of karma, Woodman is splattered with a ton of goo and has to be hosed off, much to his anger.
After bragging about Head and Shoulders coming from Arizona, Lewis introduces, Ira, Harry, Wayne and Allison as heroes for discovering a way to kill the aliens. Allison suggestive tells Ira he wouldn't miss getting recognition "for anything"; he smiles back. Both quietly back out of sight as Wayne is given a medal and told he is going to be made a firefighter; he failed his entry exam because he was forced to stay up late answering questions about the meteor. Harry is then awarded a medal, being called a "noted geologist and the winningest coach in Arizona women's volleyball" before giving a brief speech. Allison and Ira, have entered the firetruck after taking off their coats. Lewis then goes to congratulate them, only to find that they are gone. Harry tells Lewis "I think he's giving her a bit of the Kane Madness", to which he knows what that means.
The film ends with Harry, Ira and Wayne as spokesmen for Head & Shoulders with a clip of them chasing the dragon alien in the jeep while "Out With a Bang" by Self plays in the background: "Wow, Fighting the alien menace can be a tough job. And so is keeping your hair shiny and dandruff free. So it's a good thing we always keep a healthy supply of Head & Shoulders around the house!" The film ends with the dragon alien roaring and lunging at the screen.