Meet the peppered moths of the English woods,
The forests of Manchester is its neighborhood,
It’s gone from white to black and back.
Through natural selection from bird attacks.
Natural selection starts with inherited variation
Followed by selection of favored traits within a population.
If selective pressure’s consistently applied in the same direction.
The beneficial traits will become the norm,
It’s how adaptations form.
Peppered moths spend their days on the trunks of trees.
A Manchester bird will eat each moth it sees.
Protective coloration is a key adaptive trait.
A moth that stands out meets a painful fate.
In eighteen hundred that meant looking light,
‘Cause lichens on tree bark made them look so white.
So the light-colored moths in the population,
Had a phenotype to avoid predation.
Through the moth gene pool white genes had spread,
Genes for black were rare, their owners wound up dead
Then industrial pollution turned things head to foot
The lichen-whitened trees covered with black soot.
Those rare black moths started to thrive.
Instead of getting eaten every year they survived.
As the white moths were eaten, one by one,
The black ones bred it was oh-so-fun.
Each moth generation takes a year.
So soon the shift was very clear.
The dark phenotype came to predominate
And a young white moth met a painful fate.
‘Bout 1960 things turned the other way,
Humans realized pollution doesn’t pay.
With less soot in the air the lichens came back,
The tree bark in Manchester turned to white instead of black.
I’m sure you can guess what ensued
The change turned the black moths into bird food.
Today Manchester moths are mostly white,
As the birds keep on selecting, eating all black moths in sight.
In the 1950s Kettlewell proved
A moth with poor camouflage becomes bird food.
When Kettlewell’s critics created a fuss
The mechanism was confirmed by Majerus.