. . . . Now one more thing, then I intend
To move on from the subject of mutation:
A true-life story of how adaptation
Results from the environment acting on
Genetic variation. It's well known,
This story of the moth and evolution.
During the Industrial Revolution,
In nineteenth-century England, there were trees
On which some peppered moths would take their ease;
The tree trunks, lichen-covered all around,
Gave these light-colored moths a light background
On which to rest, and thus gave them protection,
For there were hungry birds whose predilection
For tasty moths was sorely hampered by
The fact these moths were so hard to espy.
But air pollution played a dirty trick
Upon the moths, for soot became so thick
That all the tree trunks started turning black,
And those light-colored moths became, alack,
Then easy prey for birds to spot. But wait!
Guess what occurred in 1848.
A mutant peppered moth appeared, a dark
Newcomer; blending with the sooty bark,
He lived a long life, reproduced, while light
Moths, once so fit, were dying left and right;
In time, his melanotic genes had spread
Till almost all the moths were dark instead
Of light, then with the tree trunks nicely blending.
Now that's what I would call a happy ending
(Although bird lovers might well disagree),
For once again the moths were hard to see.
That's how selection works, that's adaptation,
Resulting from a favorable mutation,
Preserved, in time of change and of destruction,
By way of differential reproduction.