protomolecule
Noun
Meaning
A collection of unstably bound atoms that has the potential to form a molecule if the structure can shed sufficient energy.
A relatively simple molecule from which a more complex molecule is derived.
Source: en.wiktionary.orgExamples
The aliens that sent the protomolecule hadn't needed to destroy humanity. They'd given humans the opportunity to destroy themselves, and as a species, they'd leaped on it.