Humans

Humans (人間, Ningen); short for Homo sapiens in modern biology, also known as Terrans, are a species native to their world they called Earth. Human technology is considered primitive compared to other intelligent species, such as Cybertronians. However, both Humans and Cybertronians have many different things in common, like science, history, biology and team work.

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 * —About Humans.

Anatomy and Design
Humans are built similarly to Cybertronians only being organic rather than metallic in nature.

Negative Effects from Energon
Despite having existed on their planet for years, humans are even more vulnerable than Cybertronians to the effects of Energon. This would show that human nervous systems and energon do not mix well.