During a university lecture, Professor Julian talks about Neanderthals, an extinct group of archaic humans. He explains they supposedly were very dumb and absolute savages, based on the studies of Darwin and Galton. Their theories could tell how civilized and intelligent someone was just by their appearance.
Julian disagrees, saying current humanity has a bit of Neanderthal in them. He also reveals that the world’s only non-fossilized Neanderthal was found by his boss and was named William after the scientist who recognized Neanderthals as a separate species. He finishes the lecture by pointing out it could theoretically be possible to create a living Neanderthal using William’s DNA.
Endocrinologist Barbara watches the entire lecture and later that day she looks for Julian at a restaurant. She brings up the possibility of cloning William, which would be very hard and complicated but not impossible. They spend their dinner discussing the details behind the process and by the end of the evening, Barbara is curious to know why Julian’s obsessed with Neanderthals in particular.
To answer that, Julian takes Barbara to his lab and shows her two stone tools: one was made by homo sapiens, and the other one by Neanderthals. There’s no difference between them, so Julian thinks they could learn a lot about humanity by studying our closest cousin. That night Julian and Barbara fall in love.
From then on the couple starts working on the Neanderthal cloning project and in only two years they release three ground-breaking papers on the subject. They also move in together and have a wonderful romantic life. Unfortunately many important scientists and university donors are worried about the morals behind this project and the potential backlash, so they cancel their support.
However the couple refuses to give up and Barbara decides she’ll carry the cloned embryo while letting everyone else think she’s having a normal pregnancy. Afterward the couple goes to Las Vegas and gets married by an Elvis impersonator. A few months later Barbara gives birth in the hospital.
The nurses share a disgusted look before handing the baby to the happy mother. The couple isn’t bothered by the child’s ugly appearance and Julian even kisses the boy’s forehead. Sometime later Julian drops by the university to drop some paperwork explaining what he and his wife did.
The higher-ups organize an emergency meeting, afraid of what this may do to the university’s reputation. They don’t like the project, but for now they decide to be supportive so they can get publicity and hopefully get a chance to control it. The next morning Julian organizes a press conference to tell the world about the Neanderthal clone created by using cell nuclear transfer.
A reporter asks about the morality of it, so Julian shows them a cute clip of the baby and asks how something so beautiful could be immoral. After the conference is over, Julian’s boss reminds him that the board has a final say on anything that happens to the project. Many years later, the baby is now a young man called William.
Barbara drives him to the forest and they say goodbye to each other before William leaves for his dad’s house. He looks around for a while before reaching the balcony with a great view of the river. Two tourists pass by on a boat and when they see William’s ugly face, they start rowing faster.
William goes back inside and finds the ancient stone tool on one of the shelves. Suddenly he’s startled by a noise but it’s only his new tutor Sarah. She explains Julian is at work and William can’t help feeling awkward around a stranger.
That night Julian joins them for dinner and Sarah notices William eats a lot, so Julian explains that William’s metabolism is different and requires more calories than the average person. After dinner, Julian tells William he’s proud of him for following his dreams. The next day Sarah helps William with his studies and shares she’s still working on finishing her dissertation.
William is very good at math but English is a bit hard for him because he doesn’t like metaphors, which he sees as lies. Meanwhile in the university, Julian tells his class about his project. When it all started, they had protesters complaining every day since they saw cloning as immoral and a sin against God.
However William grew up as a normal kid under the loving care of Julian and Barbara, so the protesters stopped showing up. The news stopped talking about him too since they didn’t have any interesting clickbait about savage cavemen. Theories say that homo sapiens drove Neanderthals to extension with superior intellect, but after years of studying his son, Julian doesn’t agree with that theory anymore.
William started to talk earlier than most children and developed faster, he also showed equal or even greater intelligence than his peers. One day William got sick and no medicine was working on him, but just being his mother helped him get better. It turns out his immune system is very robust and adapts fast, which promises incredible medical applications.
After his class is over Julian remembers the day he and Barbara broke up. William had been growing up inside a lab but Barbara wanted him to be free and have a normal life. However Julian kept seeing William as an experiment and reminded Barbara that he wasn’t really her son.
That comment really hurt Barbara so she finally left Julian for good. Afterward she got permission from the university board to leave with William. They moved to a new house and William was excited to have his own room.
Barbara got a job at the clinic but would still do research part-time, and Julian would visit them often. The couple still worked together to find William a good school and had to call out the principal for saying the boy wasn’t fully human. Thankfully William had a great time at school and quickly made a best friend.
Julian visited him as promised and they would play games outside, enjoying William’s new freedom. In the present, William is using his break to exercise, which shows his great strength. Sarah calls him to continue studying and reads him a quote from “The Great Gatsby”, asking him to offer his interpretation.
This ends up in an argument because William thinks nobody should get to decide what another person means except for that person themselves. Another flashback shows William riding his bike down the road when a bunch of older kids saw him. They called him “caveman” to mock him and started chasing after him.
At first it looked like William would get away, but he accidentally crashed his bike against the bridge and had to continue on foot. When the other boys tried to grab him, William pushed two of them to the ground and hurt the hand of the third. Later at the police station, the kid’s mother kept saying William was dangerous and wanted him locked up, but the cop just kicked everyone out because he couldn’t act on just some children having a fight.
When they went home, Barbara told William to walk away whenever someone mocked him to avoid trouble. Then William searched his name on the internet and found all the articles about his birth, not to mention the protests. Reading about Neanderthals showed that everyone believed them to be savages.
Eventually Barbara started dating a new man and Julian stopped staying for dinner during his visits. He also stopped running the routine tests on William and made his assistant do it instead, which made Barbara mad. Years later when William started high school, he made some good friends even though he couldn’t always understand their jokes.
During their last school year, William and his two friends decided to go on a trip together and shared their thoughts about applying to college. While they were having fun, they came across two hippies, who joined the boys around the fire and shared their mushrooms. When they realized who William was, they called him “cool” and “beautiful”.
The woman asked him if he ever wanted to go back to his own time, and William said yes. She encouraged him to “go there” while his friend threw up because of the nasty things he ate. At school William helped his crush Judy with the incoming play and even agreed to be one of the actors.
The night of the show, William played Judy’s love interest and got his first kiss as part of the story. However when he tried to kiss Judy again behind the curtain, she turned him down. The play was a success but William was heartbroken because it never meant anything to Judy.
Sometime later William’s teacher called Barbara and Julian to explain that their son was smart, but he wasn’t good with standardized tests because the way he thought didn’t match any recognizable model. He would need extensive tutoring to redo his college applications, and Julian freaked out when he realized Barbara had withdrawn the applications his son already sent. Barbara explained William got a part-time job at a hardware store to keep him busy after graduation, but Julian wanted him to be more than that.
An argument ensued and the teacher had to remind them this had to be William’s decision. Meanwhile William was saying goodbye to his friends who were leaving for college soon. That night his parents explained the situation to him.
Julian asked him to come live with him to get tutoring lessons, but that would also mean getting experimented on again. Barbara was against that, however William was desperate for a normal life and took his father’s offer. In the present Julian checks on William’s latest practice test and gets angry because it’s still not enough, blaming Sarah for it.
She points out William has made great progress and William says it isn’t her fault, only for Julian to throw the test papers in his face and leave the house. As William starts to cry, Sarah swears his scores are really good and takes him on a walk through the forest. She shares that her parents were also very strict with her when she was younger and for a long time she hated them for deciding her future without asking her, but now she can’t complain about the great education she got.
In return William admits he loves singing and shares the song from his school play. This ends up with William and Sarah kissing and getting dirty. They return to the house in the evening and Julian scolds them both for losing time instead of studying.
That night William can’t stop staring at the stone tool, wondering if he’ll ever be more than this. Sometime later Sarah takes William to a school so he can take his tests again. All the pencils he tries to use keep on breaking, so he sees this as a sign and gives up, leaving the room without finishing the test.
Then he goes to the store to get a drink and two girls laugh at him, so the clerk insults them for being rude. After a long walk, William goes to the university to see Godwin, the woman who found the Neanderthal remains. She takes him to her lab to see the body, which is being kept in a special cage for conservation.
William can’t stop staring at the body from every angle and even thinks the guy may be smiling. Godwin explains they don’t know how he died because there are no wounds or signs of illness. As for theories, she thinks that homo sapiens developed the ability to create and believe narratives, and those stories could bring groups together in large quantities.
Those superior numbers forced the Neanderthals into a less advantageous habitat, which eventually caused them to extinct. When William asks about the stories, Godwin tells him it includes everything from religion to political hierarchy, but also family stories. All the things people would go to war and die for.
William can’t understand how believing lies made homo sapiens intelligent and thinks superior numbers are the only reason why Neanderthals were driven to extinction. He announces he doesn’t belong here, and neither does the man in the box. Godwin tries to convince him he has a place, but William just walks away.
Meanwhile Sarah is searching for William and can’t find him anywhere, so she gets Barbara to help her. Moments later William sneaks into Julian’s lecture and interrupts it when his father keeps referring to his son’s life as “his work”. William calls the experiment a failure and Julian corrects him, saying it’s William who is a failure.
A devastated William runs away and Julian goes after him to apologize, saying William provoked him by embarrassing him in front of the class. William responds that Juliam embarrassed himself and that he isn’t his father, causing an angry Julian to slap him for it. Once again William tries to leave and when Julian tries to stop him, he accidentally drops the stone tool.
Both men reach for it at the same time and William suddenly punches Julian to knock him out, as if defending his belonging. As soon as he realizes what he’s done, William feels terrible. Soon students gathered around them, calling William a savage and taking pictures.
William has no choice but to run away. Moments later Barbara finds an unconscious Julian and calls Sarah to warn her that the police are looking for William. Barbara will go to the hospital with Julian so Sarah must continue her search alone.
Meanwhile William is hiding in another university building, where he’s seen by a student who calls the police. When William tries to leave, he finds a bunch of cops waiting for him with their guns out. Sarah also arrives and calls out his name, but an officer holds her back.
Remembering the bridge incident, William walks ahead and gets shot down in seconds, meeting his death. Some months later, Sarah visits the spot where Godwin found the Neanderthal. She brings a baby with her, implying it’s William’s child.
