118. Read the following passage, then answer the question below.

If intelligence is measured by behavior, the octopus is one of the most remarkable animals on Earth. It can unscrew the lid of a jar from the inside, navigate mazes, and recognize individual human keepers, squirting water at those it dislikes. Remarkably, it does all this with a nervous system organized differently from ours. Roughly two-thirds of an octopus's neurons lie not in its central brain but in its eight arms, each of which can taste, touch, and, to a degree, decide how to move without waiting for instructions.

This arrangement is the result of a very distant ancestry. The last common ancestor of humans and octopuses was a simple worm-like creature that lived more than 500 million years ago, long before complex brains existed. Intelligence therefore evolved at least twice, along completely separate paths. Biologists find the case valuable because it shows that thought does not depend on a particular design, such as a backbone or a cortex.

Why would a soft-bodied mollusk need intelligence at all? One explanation is that, having lost the protective shell of its ancestors, the octopus became vulnerable and had to survive by cunning, whether by hiding, changing color, or squeezing through gaps the width of its beak. Another is that it hunts varied prey, such as crabs and clams, which demands flexible problem-solving.

Yet the octopus also illustrates the limits of comparison. An octopus lives only a year or two, and it never meets its parents, for most species die soon after the eggs hatch. It therefore cannot learn from older members of its species as young chimpanzees do. Whatever it knows, it must discover on its own. Some researchers see this as evidence that its intelligence is exceptionally powerful; others caution that apparent cleverness may reflect curiosity or persistence rather than reasoning, and that we should resist interpreting its behavior through a human lens.

The word 'persistence' in paragraph 4 is closest in meaning to