Quirks of Evolution

Quirk of Evolution

Predetermined. Almost preordained,
by the genetic code,
by the distance of their ancestors
from each other; Darwin’s finches
In the Barbados;
a couple of miles over water,
enough to evoke the engine of difference;
Like Neanderthal and Cro-Magnon;
There wasn’t even a barbed-wire fence:
just the Pillars of Hercules .
But here, in my garden,
they are really close, fluttering first cousins
playing Ins and outs between two trees,
their branches practically interwoven.
Why is the song they sing so different?