One thing that we should consider when discussing advanced intelligences is the time scale. Imagine a sentient being whose thoughts and movements operate on a time scale a million times slower than a human's. Would we be able to recognize the being as intelligent? Would we recognize it as alive? Imagine an intelligent being who's thoughts and movements operate millions of times faster than ours. Would that being be able to tell the difference between a human and a lump of rock?

Before we speculate if something is or is not, let's clarify what's being asked. When you say "higher intelligence", what do you mean? Specifically, is higher intelligence just intelligence but more of it? When people say "higher intelligence" do they mean intelligence on a whole new level. You see, I think when people use that term they think they're being specific and not at all religious or superstitious but I find the term as vague and nebulous as "god" or "evil".

There’s ample evidence that porpoises, dolphins and whales in general have higher intelligence.

I'll pass. This is already being attempted. It's called Ancient Aliens, ugh...?

How could we, at our level of understanding prove or disprove the existence of higher intelligence? The question seems rhetorical.

The Drake Equation
[astrodigital.org]

SETI

Yes, this is the Bandwagon Fallacy, or proof by numbers.

Of course it is possible, almost anything is theoretically possible, but is it reasonable. One thing I learned on my many tours of jury duty was reasonable doubt. There can always be doubt, I mean space aliens or Satan could have come to Earth and put fake fossils in the ground, but is that reasonable? No.

We have no proof of higher intelligence yet - however its naive to think we are the only life in the Universe - some planets must have life more advanced than ours.