When writers and producers get together to create a pilot episode for a series, it's essentially one big tease of what's to come. The first episode is meant to hook the audience so they have to tune in for episode two. Because pilots are typically filmed well in advance of the rest of a series once it's picked up by a network, a lot of things can change once the series gets going.
That's definitely true for the CW's series of novels. Not only did the show differ from its source material, but budget, changes in style, and actor performances meant that a lot more evolved as the show went on.
Blood Types Of The Sky People
In the first episode, Chancellor Jaha is shot and Abby Griffin needs extra blood and medication to keep him alive. While that breaks the rules of the Ark, that's not the part that's interesting. She calls specifically for A-negative blood for Jaha.
The trouble is that all the people on the Ark have the same blood type, as revealed by the writers. They're all O-negative, making them universal donors. That's why Jasper is able to filter Maya's blood through his own system in the next season. It's likely a creative decision that was made after the series was picked up and the background of the world was expanded.
Callie Cartwig
Some fans might not even this character's name, but she does appear in a single episode of the series — the pilot. Played by Kelly Hu, she is best friend to Abby Griffin, but she's never seen or heard from again after Abby's brush with death.
That's because, according to showrunner Jason Rothenberg, the budget for the series changed once The 100 was picked up as a series. Some of the actors had to be cut, and Hu, unfortunately, ended up being one of them. In the show, her disappearance is never explained, though Rothenberg says that she had to be "floated" off camera.
Boy-Crazy Octavia
There's no question that Octavia is an intense individual. When she commits to a project or a cause, she's all in. The Octavia fans meet in the pilot is the same — but specifically when it comes to boys.
Not only does she put herself squarely in Finn's sights, but she essentially pouts her way to making sure Bellamy's okay with her following Finn around. She also spends a lot of time flirting with Jasper and showing off in front of Finn, Jasper, and Monty, trying to hold everyone's attention. Octavia goes through a drastic change once the show gets a handle on her character.
Octavia's Hair
Everyone's hairstyle changes as the show goes on, to be sure, but Octavia's change might be the most interesting. Her hair, despite having been the girl who lived under her mother's floor, is immaculate and light brown.
The farther into the series, the darker her hair becomes. By the sixth season, her hair is no longer brown, but black. Unlike Clarke, Octavia doesn't appear to spend much time dying her hair with berries or flowers.
The Tone Of The Show
Showrunner Rothenberg has actually the worst" of the show. That's not because they're bad episodes of television, but because they are so tonally different from the rest of the series.
The show has progressively gotten darker, and Rothenberg believes the series really finds its footing in episodes four and five. Episode one, on the other hand, has the tone of a teen drama rather than a post-apocalyptic epic.
Jasper Lives
In his same EW interview, Rothenberg reveals an interesting tidbit about the pilot: it originally featured Jasper's death. The script called for his ing to close the episode. As aired, the episode sees Jasper pinned by a spear from an unknown party, but his fate is left up in the air.
Actor Devon Bostick's sense of humor as Jasper was beloved by fans, so they're likely glad he got to stick around for a few more seasons.
The Ark Comes To Earth
Despite the Ark's air supply scheduled to run out in a few months during the first episode, the original plan wasn't to bring the Ark's inhabitants to Earth either. That idea came to the writers about halfway through the first season.
Rothenberg told EW that writer Bruce Miller brought it up, and initially Rothenberg was hesitant to do it because of how much it cost to build the Ark sets. Pieces of the Ark sets become the dropships sent to Earth later.
Finn's Connection To The Ark
Eventually, it's revealed to Clarke that Finn, the boy who has been pursuing her, has a girlfriend back on the Ark — one he went to prison for. That connection to their home in space isn't apparent in the pilot.
At one point, Clarke even comments on Finn trying to remove his bracelet, telling him that's how people on the Ark will know they're alive. He doesn't really seem to care much. That might be because his girlfriend Raven isn't in the original pilot script or the plan for the show. The character that eventually evolved into Raven would have been Finn's mother in the original script, but those scenes were cut.
The Radiation-Effected Fauna
Though the planet is safe for humans, there's one major way The 100 demonstrates how the radiation of 100 years ago effected the planet. The pilot episode showcases a lot of animals that have mutated from the effects.
There's the giant water snake that attacks Octavia, the two-headed deer in the woods, and the glowing insects that make for a pretty picture. None of those appear again, likely due to budgetary constraints.
The First Love Triangle
There are many love triangles that pop up in the course of the series, but the first triangle attempted is in the pilot before it's clear who Octavia's character will be. She isn't just obsessed with cute boys; she's also not afraid to tell other girls to back off.
Finn is clearly interested in Clarke, though she tries to remain indifferent to him. Octavia sees that and warns Clarke to stay away. Clarke's response is simply, "I don't care," because she's genuinely more interested in surviving than she is in Finn. Octavia, however, doesn't seem to believe her.