In agrarian(农业的), pre-industrial Europe,“you'd want to wake up early, start working with the sunrise, have a break to have the largest meal, and then you'd go back to work,”says Ken Albala, a professor of history at the University of the Pacific.“Later, at 5 or 6, you'd have a smaller supper.”

    This comfortable cycle, in which the rhythms of the day helped shape the rhythms of the meals, gave rise to the custom of the large midday meal, eaten with the extended family.“Meals are the foundation of the family,”says Carole Couniban, a professor at Millersville University in Pennsylvania, “so there was a very important interconnection between eating together and strengthening family ties.”

    Since industrialization, maintaining such a slow cultural metabolism has been much harder, with the long midday meal shrinking to whatever could be stuffed into a lunch bucket or bought at a food stand. Certainly, there were benefits. Modern techniques for producing and shipping food led to greater variety and quantity, including a tremendous increase in the amount of animal protein and dairy products available, making us more energetic than our ancestors.

    Yet plenty has been lost too, even in cultures that still live to eat. Take Italy. It's no secret that the Mediterranean diet is healthy, but it was also a joy to prepare and eat. Italians, says Counihan, traditionally began the day with a small meal. The big meal came at around 1 p.m. In between the midday meal and a late, smaller dinner came a small snack. Today, when time zones have less and less meaning, there is little tolerance for offices' closing for lunch, and worsening traffic in cities means workers can't make it home and back fast enough anyway. So the formerly small supper after sundown becomes the big meal of the day, the only one at which the family has a chance to get together.“The evening meal carries the full burden that used to be spread over two meals,”says Counihan.

Welcome to the Kids' Science Challenge!

    Do you like science projects and winning some awesome gifts? This is the challenge for you. What's even better is that you don't have to build anything--simply come up with an original idea or design that relates to one of three topics given below.

Wonderful Sounds

    Ready for Wonderful Sounds? Click on Science Secrets to meet our sound specialist. And be sure to download fun activities with crazy new sounds and musical instruments in the Dig In section! Now what kind of new musical instrument can you invent?

Super Material for Sports

    Ready for Super Material for Sports? You'll discover the amazing world of Materials Science, where scientists and engineers develop new materials for everyday functions--like sports! Click on Science Secrets for information about our scientist. And don't forget to download the fun activities in the Dig In section! Now can you come up with a new sports material that would help you play your favorite sport?

Magical Microbes

    Ready to discover Magical Microbes, the tiniest living things on earth? Click on Science Secrets for information about our scientists. And be sure to download all the fun activities in the Dig In section! Now can you think of a brand new way that microbes can help people?

    Here is a record of the discussion about AI (artificial intelligence) conducted by several scientists:

    Scientist A: I would say that we are quite a long way off developing the AI, though I do think it will happen within the next thirty or forty years. We will probably remain in control of technology and it will help us solve many of the world's problems. However, no one really knows what will happen if machines become more intelligent than humans. They may help us, ignore us or destroy us. I tend to believe AI will have a positive influence on our future lives, but whether that is true will be partly up to us.

    Scientist B: I have to admit that the potential consequences of creating something that can match or go beyond human intelligence frighten me. Even now, scientists are teaching computers how to learn on their own. At some point in the near future, their intelligence may well take off and develop at an ever-increasing speed. Human beings evolve biologically very slowly and we would be quickly substituted. In the short term, there is the danger that robots will take over millions of human jobs, creating a large underclass of unemployed people. This could mean large-scale poverty and social unrest. In the long term machines might decide the world would be better without humans.

    Scientist C: I'm a member of the Campaign to Stop Killer Robots. Forget the movie image of a terrifying Terminator stamping on human skulls and think of what's happening right now: military machines like drones, gun turrets and sentry robots are already being used to kill with very little human input. The next step will be autonomous “murderbots” following orders but finally deciding who to kill on their own. It seems clear to me that this would be extremely dangerous for humans. We need to be very cautious indeed about what we ask machines to do.

    Our cities have never been denser, taller, or busier than they are now, and with that, comes the constant battle for land. But if we look at aerial images of any city center, we can quickly spot plenty of unused space — the rooftops.

    So what can we use this precious resource for? In a growing number of high-density cities, some of it is dedicated to recreation — everything from bars and pools, to soccer pitches and running tracks can now be found atop skyscrapers. But when a rooftop offers access to sunlight, there are two more obvious candidates for its use - agriculture and solar power.

    Green roofs have been growing in popularity for more than a decade, and in some cases, growing in scale too. Green roofs can provide a habitat for birds and insects in an otherwise hostile environment.

    Cities can be several degrees warmer than the surrounding countryside. Green roofs come with the added benefit of mitigating the dreaded urban heat island effect. Trees and green spaces can absorb shortwave radiation, and use it to evaporate water from their leaves — a kind of 'double cooling' effect.

    With food security and urban nutrition ever-higher on the agenda for the United Nations, there's also a worldwide movement of using green roofs for hyper-local food production. In regions with suitable climates, hundreds of different vegetables, fruits, and salad leaves can be grown on rooftops.

    But what about solar power? With so many cities now stopping using fossil fuels, and the costs of solar panels dropping dramatically, PV systems have become the 'go to' option for generating distributed power in built-up areas. And, even with standard commercial panels, the energy gains are dramatic. It is estimated that rooftop PV systems could generate almost 40% of electricity demands nationwide.

    There's no doubt that in both cases, a network of 'productive rooftops' could benefit the local community by supplying a portion of a necessary resource — either food or electricity — while also reducing their environmental burden. But is one better than the other?

    This was the question posed by researchers from MIT and the University of Lisbon in a recent paper in the journal Cities. Focusing on the rooftops of a mixed-use neighborhood in Lisbon, they carried out a Cost-Benefit Analysis. Starting with existing data on everything from installation costs and resources used, to carbon footprint and yield, they modelled the impact that each installation would have on the local community over a period of 50 years.

    And by looking at it that way, they concluded that for Lisbon, the use of rooftops for food production could yield significantly higher local value than solar PV energy generation. Of course, this is very site-specific. There is no one-size-fits-all solution to make cities more sustainable, and anyone who tells you otherwise is massively over-simplifying a complex issue. Now, all I hope is that some of those decision makers start using it.

    There is an English saying that says, "Let Sleeping Dogs Lie." It means not bringing up an old problem. Researchers in Hungary have found another reason to let dogs keep on sleeping. It seems the animals are learning while they sleep.

    The Hungarian researchers placed tools on the dogs' heads to know about electrical activity in the brain. The brain activity, called sleep spindles(梭状波), takes place in human begins, and has been connected with learning. The researchers hope to understand how the dogs' ability to learn and remember changes as they get older. The study may help them understand how human brains change as we age.

    The researchers found differences between male and female dogs. Iotchey, a researcher, says the females appeared much better at learning new things. Female dogs have about twice as many spindles per minute as male dogs, they also happen to be the better learners, and they memorize the task much better. But it was harder for all the older dogs to remember things, especially when several things were happening at the same time.

    DoraSzabo also studies sleep spindles. Szabo is a neuroscientist in a university in Budapest. She says the older dogs have fewer spindles and are easily cheated. "If you first hide the reward into one bowl, then in another and in another, they get lost after a while. So their performance is going down, and they are getting poor in solving new problems."

    Researchers hope the study will not only help understanding of learning ability and memory changes in dogs, but also the aging of humans. Senior Researcher EnikoKubinyi adds that the aging dogs suffer from the same problems as humans who are aging. “Among very old dogs, up to two thirds of them show signs of dementia(痴呆), and this dementia is really very similar to that of humans, so we could use dog as a natural model of human aging."

    Plants are boring. They just sit there photosynthesizing (光合作用) while animals have all the fun. Right? Not so much. A new study has found that there is a long history of interactions between ants and plants. The ant and plant co-evolution (协同进化) started with ants feeding on plants and plants evolving ant-friendly features.

    Plants make a number of different structures that are specific for ant use. Some plants have evolved features that persuade ants into defending them from attack from other insects and even mаmmаlѕ. Тhеѕе іnсludе hollow thorns that аntѕ will live іnѕіdе, or ехtra nесtаr (琼浆) оn lеаvеѕ or stems for the ants to eat. Some ants will just cheat and take the nectar and run, but some will stick around and attack anything that tries to hurt the plant. Other plants get ants to help them move their seeds around, by providing them with rich food packets attached to the seeds. The ant will pick up the seed and carry it away, eat the food packet, and leave the seed—often in a nutrient-rich area where it'll grow better, and since it's farther away from its parent, they won't have to compete for resources.

    But scientists weren't sure how the evolutionary relationship between ants and plants got started. If evolution is an arms race between species developing ways to make use of their neighbors, then scientists wanted to know whether plants or ants fired the first shot. It was a chicken-and-egg question, whether things started with ants developing behaviors to take advantage of plants, or plants evolving structures to take advantage of ants.

    The history of ants and plants evolving together goes back to the time of the dinosaurs, and it's not easy to tell from fossils who fired the first shot. However, it is a question of little significance. Scientists say their study maters because it provides a look at how these widespread and complex interactions evolved.