"The controlled expression of one cellular feature -- the cilium -- was likely critical during early animal evolution. Two key transcription factors, RFX and FoxJ1, coordinate ciliogenesis in animals but are absent from the genomes of most other ciliated eukaryotes, raising the question of how the transcriptional regulation of ciliogenesis has evolved."
@cyrilpedia hey forgive me, I know nothing of your science, but permit me to take a shot in the dark here.
There are predatory cells right? I would think the antenna began evolving when the first multicellular organisms appeared. I think the first multicellular organisms were actually single celled organisms that cohabitated well. This makes a disadvantage to single celled organisms. So single celled organisms that have protrusions could defend defend better because hey, they're like bumpers. Somewhere in the middle of this single vs. multi cell war. That wasn't enough. But if 2 single celled organisms that could detect each other and behave like a multicellular organism, the balance is finally there. 1 eternity later.. multicellular organisms adapt this too. To counter this, the protrusions on the single celled organisms are not only sensory but predatory. Balance achieved again. Up till here I think they were mainly parasitic. But once they got the ability to stab consume using a sensor, this became a 2 way street. They could also inject. This provides a doorway to alternative replication. What happens when the old way is less affective? It dies off. The transcription was there once upon a time. Not needed anymore. However with complex animals, it's still a good way to go as they live longer as a community and generally protected by thick outer membranes.
Ok I'm done, you can laugh at me now for writing so much on something, I have a highschool education 20 years ago on. But I like stretching my brain in directions outside of tech.