The dogs in the past who retreated had been rejected by men.

They had not become Jerry's ancestors.

The dogs selected for Jerry's ancestors had been the brave ones, the up-standing and out-dashing ones, who flew into the face of danger and battled and died, but who never gave ground.

And, since it is the way of kind to beget kind, Jerry was what Terrence was before him, and what Terrence's forefathers had been for a long way back.
So it was that Jerry, when he chanced upon the wild-dog stowed shrewdly away from the wind in the lee-corner made by the mainmast and the cabin skylight, did not stop to consider whether the creature was bigger or fiercer than he.

All he knew was that it was the ancient enemy--the wild- dog that had not come in to the fires of man.