What is the "THEME" of the following Poem?

I am who I am.
A coincidence no less unthinkable
than any other.

I could have different
ancestors, after all.
I could have fluttered
from another nest
or crawled bescaled
from another tree.

Nature's wardrobe
holds a fair supply of costumes:
spider, seagull, fieldmouse.
Each fits perfectly right off
and is dutifully worn
into shreds.

I didn't get a choice either,
but I can't complain.
I could have been someone
much less separate.
Someone from an anthill, shoal, or buzzing swarm,
an inch of landscape ruffled by the wind.

Someone much less fortunate,
bred for my fur
or Christmas dinner,
something swimming under a square of glass.

A tree rooted to the ground
as the fire draws near.

A grass blade trampled by a stampede
of incomprehensible events.

A shady type whose darkness
dazzled some.

What if I'd prompted only fear,
loathing,
or pity?

If I'd been born
in the wrong tribe
with all roads closed before me?

Fate has been kind
to me thus far.

I might never have been given
the memory of happy moments.

My yen for comparison
might have been taken away.

I might have been myself minus amazement,
that is,
someone completely different.