Bananas and apples continue to ripen after being picked. Cherries and grapes do not. The difference between climacteric (后熟的) and non-climacteric fruits matters to fruit growers and greengrocers, who must ensures their products are in excellent condition when arriving at the marketplace. But how those differences originally came about remains unclear.

In a paper in Biology Letters, Fukano Yuya and Tachiki Yuuya of the University of Tokyo offer a suggestion. Fruits, they observe, exist to solve a problem faced by all plants - how best to spread their progeny around. Wrapping their seeds in a sugary flesh, to provide a tasty meal, serves as a way to got animals to do this for them. They do, however, need to ensure their fruits favour the animals most likely to do the distributing. They propose that climacterism or non-climacterism is a way to achieve this. If ground-living animals are the main distributors, then the continuing ripening of fallen fruit is beneficial. If, by contrast, those distributors are tree-living or flying animals, which can feed on unfallen fruit, then non-climacteric fruits will do well.

To test their idea, the two researchers combed through 276 papers about 80 sorts of fruits. They discovered 35 of these fruits were eaten by both groups of animals. But of those where one group or the other were the dominant consumers, 15 of the 19 eaten mainly by ground-living animals were climacteric.

Their assumption is strengthened by other evidence. They point out non-climacteric fruits tend to have vivid colors which may help them stand out amid the leaves, advertising their presence. Climacteric fruits are generally better hidden, making them harder to spot until they have fallen to the ground.

When I was a child, the new year's activity for my family is dumpling-making, but it's been years since I've last experienced the uniquely carefree comfort and connection I felt during moments. My family has changed a lot, and gatherings like these simply don't come together with the same ease as they once did.

This year, I came home in the evening to a dark house with pieces missing. I noticed things that I wouldn't have before, like how my family slept earlier and got up later and how my dog had more trouble jumping up on my bed. After all, it's easier to become blind to its subtle changes when you occupy it virtually every day of the year, and much harder when you must be exposed to months of accumulated change all at once.

Personally, the most precious childhood privilege is not the free extra snacks from flight attendants, but the privilege of thinking of the people and relationships around you with a sense of permanence. I mean this in the sense that it escaped my eight-year-old brain to think about how my parents were aging as I did or about the sacrifices they made for me until suddenly, I was an adult as they were.

I turn 20 in a couple months, so I've been seized with a feeling of adulthood, which feels far stronger than the transition into legal adulthood at 18 ever felt. It seems as if the "teen" part of"19"keeps me attached to the same category as the one my newly 13-year-old self occupied, carrying with it a certain comfort in the social allowances made for the immaturity inherent (固有的) to youth. But marching into 20 is different.

I'd so desperately wanted to move away and get a taste of independence upon starting college, but now I know that such freedom comes with loss and responsibility. Now I start to understand the governance of a circularity (循环) inherent to our lives and have a newfound appreciation for the things that remain the same.

Recently I bought a book about signposts.  Signposts aren't very interesting, you're thinking. Well, that, of course, depends on whether you happen to be lost! Ancient travelers would have been grateful for these when settlements were smaller and further apart. In winter, the ability to reach shelter for the night could be the difference between life and death. 

One of the very earliest waymarks discovered is in Cumbria. Dating from Roman times, it had lain fallen until 1836, when a farmer ploughing his fields came across a sandstone shaft(碑文). There are other stone posts that have stood by roadsides for centuries. It wasn'tuntil 1697 that an act was passed declaring that guide-stones must be built. 

This applied to remote parts of the country where there might be confusion as to which path led to the nearest market town. Later, with the appearance of the Royal Mail, the number rose still further. Nowadays many of these early road signs are designated(指定)as Listed Monuments. 

"How times change!" Lucy, an enthusiastic walker, to whom I loaned the book,exclaimed. 

"I suppose now we all rely far more upon mobile phones to guide us. "

"Yet they aren'tperfect. Whenever I go out, I prefer a map. I never have to worry about running out of battery. " "T'm always grateful to whoever is placing way-markers along the route," she added,"I suppose that however sure we are, a little outside confirmation is always welcome. "

Lucy is quite right there. Life itself can offer us a great many choices of path, and sometimes it isn't easy to know if we've chosen the best one. 

Perhaps when it comes to gratitude, we should also include thanks for those people who appear in our lives when we most need them—either giving us gentle warning that we might be heading in the wrong direction, or reassurance that we are on the right track. After all, we'd be lost without them!