According to the Encyclopaedia Britannica, the condition is the darkness in an animal’s skin, feathers, or fur is acquired by populations living in an industrial region where the environment is soot-darkened. It can be gene related
It does, however, mean that the probability that its members will survive and reproduce is enhance.
The condition evolves over the course of several generations.
But due to being lighter in colour, they become more conspicuous to predators.