Human beings aren’t the only animals that need sleep. Other mammals do too, and scientists have found that many animals, including even insects and worms—with no brain—regularly enter inactive states that look like sleep.

Neuroscientists have evidence that sleep plays a central role in the function of the brain. Sleep is involved in clearing metabolic (新陈代谢的) wastes from the brain, contributes to regulating the immune system, and is involved in the changes to the brain that happen during learning and the creation of memories. That’s why the discovery that animals without brains sleep too came as a surprise to researchers.

In 2017 a group based in the United States reported that jellyfish regularly enter a sleep-like state of inactivity, from which it is hard to arouse them. In 2020 another team, from Japan, reported a similar discovery in related animals called hydra (水螅). Hydra and jellyfish are both part of an animal group called cnidarians (刺细胞动物).

Cnidarians are simple animals whose bodies are controlled by a nerve network without a central brain. Though they lack a brain, the nerve cells of cnidarians are much like ours, and the hydra researchers found some important physiological similarities between hydra sleep and human sleep.

They showed that substances like melatonin (褪黑素), which promote sleep in humans, also do so in hydra. They also found that some of the genes involved in sleep regulation in humans perform similar jobs in hydra.

What this tells us is that sleep and probably some of its functions are important for all animals, even if they don’t have a brain. The basic molecular (分子的) mechanisms for sleep probably evolved long before brains and centralized nervous systems.

On Sunday a few of us decided to take advantage of the first sunny day we’d have for ages to take a trip down to the coast to visit the penguins again. Last time I went down there was a couple of months ago and it was a dull cold day. Sunday couldn’t have been   more different — clear skies and sunshine made it feel like summer, although it was still -25°C.

Six of us drove to the coast. It was the first time we’d been off the base on our own without our field assistant, so it had a slightly different feeling — more like a few friends going to the seaside than an

Antarctic field trip! When we reached Windy Creek, we luckily caught sight of quite a few small flying seabirds, which are seldom seen there. Once on the sea ice we found that some of the more curious penguins had wandered over from the main group to come and check us out. We’d been told that then they were nursing their chicks and they would be   more careful and nervous than last time, but that didn’t seem to be the case. We walked across to the main group which were stretched for a couple of miles along the coast. We sat down for some sandwiches and soon found ourselves surrounded by many curious observers. Without any attackers on

Before heading back, we spent a few hours on the sea ice watching the penguins and their chicks, which had grown dramatically since our last visit. It was such a nice day.

Young trees don’t just grow; they develop a personality and learn more about their environment and how they should best behave in it. They also help each other out whenever there’s trouble.

Personality, just as among people, varies among trees. Some are anxious, some bold. On the author’s land, there are three oak trees growing close together. One of the oak trees always starts to shed its leaves two weeks earlier than the others. Since they all experience the same temperature, the same soil and the same length of day, such variables can’t be the explanation. So what’s happening? Well, this tree is simply more careful than the others. Whoever holds on to their leaves longer can do more photosynthesis(光合作用) and store more nutrients. However, the longer a tree keeps its leaves, the higher the risk of injury.

Not only do trees make their own decisions, they also learn from their mistakes. A tree, for example, keeping its leaves too long during one year will never make this mistake again. This leads to several other conclusions:trees must notice the temperature and the length of the day and be able to save their experiences somewhere. Obviously, trees don’t have brains, but it is thought that in the sensitive tips of their roots they keep track of information and experiences.

But trees aren’t only clever when it comes to caring for themselves. They also support each other whenever there’s trouble by giving warnings and even taking care of sick and weak conspecifics with nutrients. For example, one time the author found a very old tree stump. Its insides had rotted a long time ago to topsoil. But the wood on the outside of the stump was still living. How was this possible? Well, the stump was nourished by its neighbors with nutrients from the root system, and had been for at least 400 years!

Why do trees do such a thing？It’s simple: it’s better together. Trees need the forest; it protects them from storms, provides the right microclimate and warns them of attacks.