“Yes, because in that environment—where the birch trunks were silver—
the darker hue was an unfavorable characteristic. So it was always the paler
peppered moths that increased in number. But then something happened in
that environment. In several places, the silvery trunks became blackened by
industrial soot. What do you think happened to the peppered moths then?”
“the darker ones survived best.”
“Yes, so now it wasn’t long before they increased in number. From 1848
to 1948, the proportion of dark peppered moths increased from 1 to 99
percent in certain places. The environment had changed, and it was no longer
an advantage to be light. On the contrary. The white ‘losers’ were weeded out
with the help of the birds as soon as they appeared on the birch trunks. But
then something significant happened again. A decrease in the use of coal and
better filtering equipment in the factories has recently produced a cleaner
environment.”
“So now the birches are silver again?”
“And therefore the peppered moth is in the process of returning to its
silvery color. This is what we call adaptation. It’s a natural law.”
“Yes, I see.”
“But there are numerous examples of how man interferes in the
environment.”
“Like what?”
“For example, people have tried to eradicate pests with various
pesticides. At first, this can produce excellent results. But when you spray a
field or an orchard with pesticides, you actually cause a miniature
ecocatastrophe for the pests you are trying to eradicate. Due to continual
mutations, a type of pest develops that is resistant to the pesticide being
used. Now these ‘winners’ have free play, so it becomes harder and harder to
combat certain kinds of pest simply because of man’s attempt to eradicate
them. The most resistant variants are the ones that survive, of course.”
“That’s pretty scary.”
“It certainly is food for thought. We also try to combat parasites in our
own bodies in the form of bacteria.”
“We use penicillin or other kinds of antibiotic.”
“Yes, and penicillin is also an ecocatastrophe for the little devils.
However, as we continue to administer penicillin, we are making certain
bacteria resistant, thereby cultivating a group of bacteria that is much harder
to combat than it was before. We find we have to use stronger and stronger
antibiotics, until . . .”
“Until they finally crawl out of our mouths? Maybe we ought to start
shooting them?”
“That might be a tiny bit exaggerated. But it is clear that modern
medicine has created a serious dilemma. The problem is not only that a single
bacterium has become more virulent. In the past, there were many children
who never survived—they succumbed to various diseases. Sometimes only
the minority survived. But in a sense modern medicine has put natural
selection out of commission. Something that has helped one individual over a
serious illness can in the long run contribute to weakening the resistance of
the whole human race to certain diseases. If we pay absolutely no attention to
what is called hereditary hygiene, we could find ourselves facing a
degeneration of the human race. Mankind’s hereditary potential for resisting