It’s a popular belief that a fish’s memory lasts for only seven seconds. It may seem sad to think that they don’t remember what they’ve eaten or where they’ve been, and they don’t identify you or any of their friends -- every moment in their life would be like seeing the world for the first time.

But don’t be so quick to feel sorry for them. A new study has found that fish have a much better memory than we used to think. In fact, certain kinds of fish can even remember events from as long as 12 days ago. In the study, researchers from Mac Ewan University in Canada trained a kind of fish called African cichlids to go to a certain area of their tank to get food. They then waited for 12 days before putting them back in the tank again. Researchers used computer software to monitor the fish’s movements. They found that after such a long break the fish still went to the same place where they first got food. This suggested that they could remember their past experiences.

In fact, scientists had been thinking for a long time that African cichlids might have a good memory. An earlier study showed that they behaved aggressively (挑衅地)in front of certain fish, perhaps because they remembered their past “fights”. But until the latest findings, there was no clear evidence.

Just as a good memory can make our lives easier, it also plays an important part when a fish is trying to survive in the wild. “If fish are able to remember that a certain area contains safe food, they will be able to go back to that area without putting their lives at risks,” lead researcher Trevor Hamilton told Live Science.

For a long time, fish were placed far below chimpanzees, dolphins and mice on the list of smart animals. But this study has given scientists a new understanding of their intelligence.

It is not always easy to understand animal behavior, especially when it’s related to other species. For decades, researchers have observed orcas (虎鲸) attacking and even killing porpoises (鼠海豚) in the Pacific Northwest. But it confuses people that these expert hunters don’t eat them. So what’s going on here?

Southern Resident orcas are a different population of orcas that live in the Pacific Northwest. The lives of these orcas are closely tied to those of the salmon. So if the salmon disappear, so too will the orca. But despite their preference for the salmon, these whales are known to attack and kill other smaller marine mammals (海洋哺乳 动物) without eating them.

To better understand this unusual behavior, an international team of researchers did a research and examined more than 60 years of recorded interactions between Southern Resident orcas and porpoises in the Salish Sea.

“Why don’t the Southern Residents just eat porpoises instead?” Deborah Giles of Wild Orca said. “It’s because fish-eating killer whales have a completely different ecology and culture from orcas that eat marine mammals. So we must conclude that their interactions with porpoises serve a different purpose, but this purpose has only been a guess until now. ”

According to Giles and her colleagues’ work, the orca may be attacking the porpoise as a form of social play. It is possible these large animals may be attacking the smaller mammals as a way to build up social cohesion (凝聚力). Similarly, the behavior could represent hunting practice, by which the orcas are practising their teamwork and cooperation skills for hunting salmons. Finally, the behavior could be a way of “mismothering” where the orca see the smaller porpoises as weaker or ill and so in need of care.

This work highlights the need for the protection of salmon populations in the area as well as the orcas’ entire hunting range. The threat to the salmon’s future is not just a threat to a single species, but an entire ecosystem.

The first apes evolved 20 million years ago in the forests where they would go up a tree to get their food, and then come back down to move on to the next tree. Getting out of a tree presents all kinds of new challenges. Big apes can’t afford to fall because it could kill or badly injure them. Natural selection would have favored those with body structures that allowed them to descend safely.

Dartmouth researchers report in the journal Royal Society Open Science that apes probably evolved free-moving shoulders and flexible elbows to slow their descent from trees as gravity pulled on their heavier bodies. These flexible body parts passed on from ancestral apes would have allowed early humans to climb trees at night for safety and comedown in the daylight unhurt. When early humans transitioned from forests to open savannas (热带稀树草原), flexible shoulders and elbows were crucial for gathering food and using tools for hunting and defense.

The researchers used sports analysis and statistical software to study how primates(灵长目动物) like chimpanzees and small monkeys called mangabeys climbed in the wild. They found that chimps and mangabeys scaled(攀爬) trees similarly, with shoulders and elbows mostly bent close to the body. When descending, however, chimpanzees extended their arms above their heads to hold on to branches, much like a person using a ladder, to counteract(抵消) their heavier weight pulling them downward.

Luke Fannin, the lead author of the study, emphasized that their findings highlight the importance of “down climbing” in the evolution of apes and early humans. He explained, “Our research introduces the idea that down climbing played a significant role in shaping the structural differences between monkeys and apes, which eventually manifested in humans.”

“Our field has thought about apes climbing up trees for a long time, but we’ve been ignoring the second half of this behavior,” said Professor Jeremy DeSilva, “The findings are among the first to identify the significance of “down climbing” in the evolution of apes and early humans.