The author doesn’t compare the level of threat created by the absence vs. the presence of predators. Although the author does suggest that certain defensive behaviors might disappear after a long time, such that an animal might not react defensively if it encounters a certain kind of predator, the author never suggests that this means the absence of a predator can be just as harmful to an animal as the presence of predators. Keep in mind that the arctic ground squirrel’s behavior disappeared because it doesn’t encounter rattlesnakes under normal conditions; so the disappearance of anti-rattlesnake behavior doesn’t actually constitute a significant threat to the squirrel.

The author doesn’t suggest that over half (most) of wild animals living today have relict behaviors. Although the author gives several examples of animals that engage in relict behaviors, this doesn’t imply that most wild animals have relict behaviors.

Supported. The ground squirrel’s anti-rattlesnake behavior, if it is a relict behavior, might disappear, as shown by the arctic ground squirrel’s inability to recognize the danger posed by a rattlesnake.

Not supported, because we don’t know that period reinforcement will make a relict behavior last forever (interminably). Although there’s evidence that absence of reinforcement can lead to the disappearance of the behavior, this doesn’t imply that the presence of reinforcement guarantees the behavior won’t disappear.

Not supported, the author doesn’t present evidence that anything “invariably” (always) occurs. In addition, the author doesn’t present any information concerning how long behaviors took to emerge. So we can’t support a comparison between how long behaviors take to emerge and how long they take to disappear.