Do animals have feelings?

People often assign feelings to animals. That zoo polar bear’s vacant stare must mean he’s sad. The uh-oh expression a dog flashes after knocking over the garbage indicates shame. But scientists haven’t determined whether these human-like expressions really mean anything. After all, it’s very difficult to read a dog’s mind.

Scientists believe that certain brain cells in humans called spindle cells (棱形细胞) are responsible for human social behavior and the interplay between thoughts and feelings. Studies have revealed that chimpanzee, dolphin and whale brains also possess spindle cells. 【小题1】

Even animals that don’t have spindle cells, such as dogs, have shown behaviors that can suggest a human-like social sense. 【小题2】 Scientists report that this shows dogs are sensitive to human social cues and are able to correctly interpret them. Still, this only proves that dogs know how to find food, not that they have feelings.

Observations of apes have also revealed behavior that appears to represent various human-like desires. In some tests, chimpanzees demonstrate what looks like altruism (利他主义) helping their own kind and even other species without the expectation of a reward.

【小题3】 In a recent study, a Barnard College researcher tested dogs to see if their guilty looks were linked to actual bad behavior. Dogs were tempted with a treat and told by their owners not to eat it. The dog’s owners weren’t allowed to see whether their pets had eaten the treat or not, but were told either that they did or that they didn’t, and were then instructed to scold the dogs that disobeyed. The experimenters noted that scolded dogs showed a guilty look whether or not they had actually done wrong.

【小题4】 A guilty look suggests a feeling of guilt in a human but not necessarily in a dog, according to the Barnard research. Similarly, even apparent empathy (共情) behavior might not actually mean these feelings are present in the brains of animals.

A new study has found that animals play dead for long periods of time in order to escape capture from their predators. How long they are motionless depends on the circumstances, but they can wait out their predators for quite a long time when their lives are in danger.

Animals stay still to avoid capture for different lengths of time. "Most interestingly, Charles Darwin recorded a beetle that remained motionless for 23 minutes. Antlions, our favorite study creature in this regard, set a record of 61 minutes," says lead author Nigel R. Franks from the University of Bristol.

Antlions are members of a large group of insects. Antlion larvae（幼虫）dig pits in loose soil and then aggressively attack ants and other small insects that fall into the sandy pits. In another study, researchers dug sandpits to understand the physics of how antlion larvae build their pits. As part of their research, they needed to weigh the individual larvae. When they put them onto the microbalance scale to weigh them, they noticed that the larvae remained motionless for long periods of time. "This made it 'a piece of cake' to weigh them but it aroused researchers' curiosity, 'What on earth were they playing at?'" Franks says.

The researchers found that the amount of time the antlions remained stationary after being disturbed was unpredictable and was often quite lengthy. In researching other animals, they found that how long they wait to move again can depend on factors such as hunger and temperature, but it always varies.

This unpredictability is absolutely crucial for their survival, Franks says. For example, if a bird visits these antlion pits and the larvae "play dead", the birds will fly around the antlions to see if they move. "Imagine if antlions always remained immobile for 5 minutes. In such a case, the predator could look for alternate prey（猎物）and then return to its original one when the time is up," he says. "If that happened, it would be a short life for the predictable antlion." But because the time is unpredictable, the birds leave and go find something else to eat. The predators turn their attention from the unmoving prey that no longer catches their eye to something nearby that is a better alternative.