When looking at Earth at the diversity of the different shapes and forms of
life.
The ant for example - very small - does not breathe.
The whale - the giraffe - the bird - the hedgehog - the crocodile - the
human or monkey.
There is considerable diversity within the eco system or environment of
Earth.

Now consider another planet - another form of eco system and then consider
how diverse alien life could be.

If life is as as diverse as say the ant as compared to the human in one eco
system on one planet - then how different could alien life be to humans?

Humans have very little imagination and are a very dull and boring and
indeed stupid and shortsighted species.
Their depictions of aliens on TV shows and books and movies - are normally
either completely ridiculous and laughable - or else aliens look rather
similar to them and they just happen to speak perfect English.