Humans are a species native to their world they called Earth. Human technology is considered primitive compared to other intelligent species, such as Cybertronians. However, Humans and Cybertronians have many different things in common, like science, history, biology and team work.
Relations with Cybertronians
The Autobots and Decepticons are divided on the subject of humans. The Autobots wish to protect humans while the Decepticons viewed them as insignificant pests. Prior to meeting Jack, Miko and Raf, Arcee and Ratchet thought protecting humans would result in more tragedies like Cliffjumper's death at the hands of Starscream.
The majority of humans are unaware that Cybertronians exist on their own planet. The U.S. government is aware of both sides and is an ally to the Autobots, though the majority of humans are wary about trusting them. MECH, became aware of them after trying to secure the DNGS. Many other humans have caught Cybertronians on camera in robot and vehicle mode (mostly Bumblebee), but have been removed by Raf using Cybertronian software and his computer expertise.
Negative Effects from Energon
Despite having existed on their planet for years, humans are even more vulnerable than Cybertronians to the effects of Energon. Agent Fowler was zapped with an Energon rod that would have tickled a Cybertronian and went into a daze. He felt pain and screamed from the zap. This would show that human nervous systems and Energon do not mix well. Raf was riding in Bumblebee and was struck by Megatron. The blast had no lasting effect on Bumblebee, but Raf was near death. This was revealed to be an infection of Dark Energon due to the substance flowing through Megatron. Ratchet used Bumblebee's Energon to aid the impaired Raf and it saved his life.
Humans require food and water to live on Earth. If they made contact with Energon, they could be harmed severely. If they were infected with Dark Energon, then Energon can help them with the help from a special doctor with extensive knowledge on Energon medicine.
Humans are built similarly to Cybertronians only being organic rather than metallic in nature. The height of humans is considerably smaller. Arcee, being the shortest known Cybertronian, is 16ft tall and is still roughly 3 times the size of an average human.
When Predacons walked among them, the creatures became the basis for many creatures in human mythology. While they possess a mythology as Cybertronians do, it is unknown if they revere a creator as the Cybertronians do with Primus. Humans are viewed as the progeny of Unicron as he is the core of their planet although the being himself had apparently no involvement in their birth and views the humans as parasites on his skin. As he stirred he was going to kill them using natural disasters and then kill any survivors by cracking the Earth's surface and leaving to go off into space (probably to kill Primus and destroy Cybertron). He was thwarted by the alliance between Optimus and Megatron. Megatron used the Dark Energon in his spark to fool Unicron's immune system while Optimus unleashed the power of the Matrix of Leadership into Unicron's spark.
When Megatron had the Omega Lock, he planned to rule two worlds, one Primus (Cybertron) and the other Unicron (Earth) as they were two sides of the same coin. His plan was ruined when Optimus Prime destroyed the Lock using the Star Saber.
When the new Omega Lock was built the Decepticons decided to use it to eradicate humanity by Cyber-forming Earth. Starscream was quite glad to have humans gone, though Knock Out praised humanity's ability at making automobiles. The Autobots saved humanity by killing Megatron and claiming the Lock. When the Autobots left for Cybertron, humanity was left to Unit: E, which was joined by Ratchet and the children.
Despite not being in the movie, the humans were mentioned by Optimus in Predacons Rising.
Years after Cybertron was restored, Bumblebee, Sideswipe, and Strongarm headed for Earth where they met up with two humans named Denny Clay and Russell Clay. Later on in the show, Russell makes friends with Hank and Butch. Arnold and his group of Kospego followers appear in As the Kospego Commands!.
Main Article: Humans Gallery