5.Why Do Birds Migrate?
5.为何鸟儿会迁徙？
We know that birds migrate over really long distances every year to lay eggs or to escape harsh winters. What we don't know is how they do it at all. The migration of birds remains one of the most mysterious animal behaviors known to science, and even though they've been trying hard to solve it for a long time, answers haven't been easy to come by.
鸟儿每年都会迁徙至很远的城市繁殖、过冬，没有人可以解释它们这样做的原因。鸟儿的迁徙至今仍为科学界未解之谜，即便多年来人们想尽办法去研究这个问题，答案仍未揭晓。

Consider this: Cuckoos migrate and lay their eggs in other birds' nests, then just fly away to their own business. When the young ones grow up, they make their way to their ancestral lands without any help whatsoever. Scientists do believe that they are able to use a variety of compasses based on the stars and the Earth's magnetic field, but a compass can only guide you—it can't tell you the coordinates of a location you should have no idea about. Clearly, cuckoos are one species you don't want to mess with.
试想一下，布谷鸟迁徙，将蛋产于别种鸟的巢中，便过着自由自在的日子。而布谷鸟的幼子长大后，却可以在没有父母的指引下，飞回它们祖先栖息的土地。科学家相信布谷鸟可以借助星星的位置或者地球磁场来辨别南北方向，但指南针只可以引导方向而不能带领你去一个你根本不知道的地方。显然，布谷鸟会是一个你并不想惹的物种。

4.What Causes Gravity?
4.引力是如何产生的？

Newton pioneered the study of gravity over 350 years ago, and you'd think that we'd have it all figured out by now. But the more we've progressed in our knowledge of the world, the more baffling gravity has become for researchers. For starters, we know the causing particle for each of the four fundamental forces of the universe—except gravity. A graviton is believed to be that particle, but we're pretty far from actually finding it.
牛顿在350年前开创了力学研究，你可能会认为人类已研究清楚所有关于力学的问题。但当人类对世界了解得更多，令人疑惑的力学问题也随之增多。一开始，人类甚至不知道四大基本力（万有引力，电磁相互作用力，弱相互作用力，强相互作用力）中的万有引力。很多人认为万有引力是微粒，但人类所掌握的知识远远未能证明此设想。
Another thing about gravity is that it is the weakest of all the other fundamental forces, yet if we look around the world, that doesn't seem to be the case at all. Gravity keeps galaxies together, and it is about 1040 times weaker than the electromagnetic force. The fact that it's so weak makes it all the more difficult to study it in the lab.
另一个有关引力的说法是：引力在四大基本力中最弱。当我们仔细观察这个世界时，这一说法似乎不可信。引力使星系聚集，但引力却比电磁相互作用力弱1040倍，亦因为引力微弱，在实验室难以研究。

3.How Do We Store And Retrieve Memories?
3.人类如何储存与检索大脑中的信息？

Science has come a long way toward understanding how our bodies work, but memories are still one of the most perplexing problems of the human anatomy. We just have no idea exactly what parts of the brain are involved in the storage of our memories, though we do know that a lot of areas of the brain are involved in the process. Even more confusing than memory storage is memory retrieval. Scientists have been looking into how our brains trace a particular memory from our memory bank since at least the '20s, but it's still not clear how we do it.
科学研究人类身体机能运作已取得很大进展，但大脑记忆仍是人体解剖学中最复杂的问题。即便我们已经知道大脑很多区域都参与记忆，大脑哪一部位与记忆有直接关系则仍未知晓。相比之下，记忆检索比记忆储存更令人费解。科学家在20世纪前已开始研究脑部如何检索特定记忆，至今仍无结论。
What we do know for sure is that it has something to do with neurons and the connections between them. When we see something that triggers a memory to be traced, many parts of the brain interact with each other simultaneously to make us remember it. Beyond that, though, the whole thing is a mystery.
可以确定的是，记忆检索与神经元和两者之间的联系有关。当我们看见触发记忆的事物，在大脑各领域的相互作用下，大脑做出记忆。除此之外，一切都只是一个谜。

2.Why Do Women Go Through Menopause?
2.为何女性有更年期？

Menopause defies all the rules of evolution. The ability to reproduce in the animal kingdom ensures that the species are able to pass on their superior genes, but in humans, something weird happens. Women decisively lose their ability to pass on their lineage at the age of about 45–50, and science just doesn't have any idea why. From an evolutionary perspective, it is always harmful for a species to completely give up their ability to reproduce, as survival by natural selection ceases to take place once that happens.
更年期不符合演变规律。在动物王国中，再生功能使物种传递优异基因。但奇怪的事情发生了，人类女性在45～50岁时失去了传递基因的能力。从进化论的观点来看，放弃生育能力对于任何一个物种来说都是有害的。一旦这种情况发生，自然选择不再有效。
One explanation is the grandmother hypothesis, which says that after a point, women should spend more time caring for their grandchildren than their children, but the benefits of that are far inferior to the benefits of giving birth to your own children. It's also not abundantly found in the animal kingdom. Apart from humans, only two species of whale completely stop breeding at a certain age and go on to live for a significant amount of time. Other animals that experience deteriorating sexual abilities, however, often die out soon after.
一种解释是祖母假说：当女性到了一定年龄时，应花费更多的时间去照顾孙辈而不是儿女，但这样做并没有比生育自己的孩子得到更多的好处。“祖母假说”也很少出现在动物世界当中。除了人类，只有两类鲸会在在特定年龄完全失去生育能力，并能生存很长一段时间，而其他动物性功能衰退后很快就会死去。

1.What Are Dreams?
1.梦是什么？

Dreaming is one thing that's common to us all. It might differ in the way it happens for some of us, but it's definitely a resident feature of all of our brains. You'd think that science would be able to figure out why our brains decide to go in LSD mode every night, but sadly, there are no definite answers as to what exactly dreams are. Some people believe that they're just random images which serve no purpose, while others believe that they carry a deeper meaning, though we're all pretty much guessing here.
梦对于所有人来说都不陌生。对于我们的大脑来说，梦是一个固有特征，不同的只是梦的内容。也许你认为科学可以解释大脑为何每晚都大屏幕播放图像，不幸的是，科学也无法给出梦的定义。一些人相信，梦只是一些没有意义的随机影像，而有人则认为梦有更深的含义，但大家的猜想并无根据。
Some theories suggest that dreams are a manifestation of things we'd rather not think about during the day, like sexual fantasies, though many modern scientists don't agree with that. What they do agree with, however, is that dreams are most likely symbolic of something deep in our psyche, though no one can decisively say what. The jury is divided on whether they serve any purpose at all, and it looks like it's going to take a long time for us to come to a universally accepted answer.
有理论提出梦展现了我们在白天不会想的事情，例如性幻想。但许多近代科学家并不认同此理论。大部分人则认为梦是人类灵魂深处的象征，但没有人可以准确说出是什么。人们对梦是否有意义的看法仍有分歧，普遍接受的理论出现还需要一段时间。

翻译：陈夏瑾 来源：前十网