Where does “ネタ” come from?

ネタ (Japanese) comes from Japanese 種, from Proto-Japonic tanay — seed.

ネタ (Japanese): material or ingredients to make something; ideas...

Definitions

Step	Language	Word	Meaning
1	Japanese	種	a seed; a pit or stone in a fruit; a gamete
2	Proto-Japonic	tanay	seed