telos

"You mean that universal explanation for all mysterious
disappearances, 'the cat did it'?" said Arthur.

"Yes," she replied. "What a convenient thing it would be if all
thieves had the same shape! It's so confusing to have some of them
quadrupeds and others bipeds!"

"It has occurred to me," said Arthur, "as a curious problem in
Teleology—the Science of Final Causes," he added, in answer to an
enquiring look from Lady Muriel.

"And a Final Cause is—?"

"Well, suppose we say—the last of a series of connected events—each of
the series being the cause of the next—for whose sake the first event
takes place."

"But the last event is practically an effect of the first, isn't it?
And yet you call it a cause of it!"

Arthur pondered a moment. "The words are rather confusing, I grant
you," he said. "Will this do? The last event is an effect of the
first: but the necessity for that event is a cause of the necessity
for the first."

"That seems clear enough," said Lady Muriel. "Now let us have the problem."

"It's merely this. What object can we imagine in the arrangement by
which each different size (roughly speaking) of living creatures has
its special shape? For instance, the human race has one kind of
shape—bipeds. Another set, ranging from the lion to the mouse, are
quadrupeds. Go down a step or two further, and you come to insects
with six legs—hexapods—a beautiful name, is it not? But beauty, in our
sense of the word, seems to diminish as we go down: the creature
becomes more—I won't say 'ugly' of any of God's creatures—more
uncouth. And, when we take the microscope, and go a few steps lower
still, we come upon animalculae, terribly uncouth, and with a terrible
number of legs!"