Is καί part of the text (Phil 2:4)?

Philippians 2:4

μὴ τὰ ἑαυτῶν  ⸀ἕκαστος  ⸁σκοποῦντες ἀλλὰ  °[καὶ] τὰ ἑτέρων ⸀ἕκαστοι.

"Each person should look out not only for his own interests, but also for the interests of others."

The question of textual criticism is whether or not the καί should be included. If it is not included, was Paul just unclear or did he expect the reader to read with common sense?