Although we spend one-third of our lives in bed, we hardly ever think about beds. While we may consider them little more than a mattress(床垫), pillow and blanket, they in fact have a fascinating history.

The first beds were hollows(坑洼) dug in cave floors by our African ancestors around 77,000 years ago. The basic idea of the bed and its structure have remained the same for thousands of years. Malta and Egypt were using raised frames with mattresses 5,000 years ago, according to Brian Fagan, the author of What We did in Bed. Early Egyptian beds consisted of wooden frames with legs and a leather sleeping platform. The mattress was little more than a sack(袋子) with grass, straw and hay in it. In Mongolia and China, heated stone platforms called kang were used in inns as early as 5000 BC.

The basic idea of who slept in the bed, however, has changed a lot through the years. Many family members or friends sleeping together in a single bed used to be completely normal for much of human history. Travelers would not expect privacy at inns. In fact, they had to share a bed with complete strangers. The greatest example of this was the Great Bed of Ware, a huge bed built in 1590 for an English inn. “A total of 52 people—are said to have spent a night in the Great Bed in 1689,” according to Fagan.

Throughout the 19th century, beds gradually became a private space. Rapid urbanization during the Industrial Revolution sped up this process as compact row houses were built with small rooms, each for a different purpose, including sleeping. So the next time you head to bed, be thankful you have your own.

Zoos have been around for centuries — and they’ve changed a lot over the years. In the Middle Ages, wealthy people kept animals in their gardens. Public animal parks appeared in European cities in the late 1700s and early 1800s. The Philadelphia Zoo, the first in the United States, opened in 1874.

Until a few decades (十年) ago, most zoos were organized by creatures — monkeys in one area, cats in another, birds somewhere else, just like museum collections. In recent years, zoos have instead begun grouping animals that would normally interact (互相作用) in the wild. Moreover, instead of closing animals behind bars, designers are creating landscapes like the environments in which these creatures would naturally be found. Nearby signs provide information about the animals and their habitats in parts of the world where they normally live.

The Denver Zoo’s new Predator Ridge exhibit, for example, aims to teach visitors about Africa. Eight acres of land provide homes for 14 animal species, including lions, porcupines, cranes, and wild dogs. Plants from the region grow alongside African-like landform. Ten-foot-tall mounds (土墩) give lions a place from which to survey their surroundings, just as they would do in the wild.

Landscape design makes visitors to the Denver Zoo’s Predator Ridge exhibit feel like they’re really in Africa.

Animals in Predator Ridge can’t actually be mixed with one another, for safety reasons. But hidden deep channels and other smart features allow visitors to see all the animals at once. Different species can see each other too.

The first drawings on walls appeared in caves thousands of years ago. Later the Ancient Romans and Greeks wrote their names and other things on buildings. Modern graffiti (涂鸦) seems to have appeared in Philadelphia in the early 1960s, and by the late sixties it had reached New York. The new art form really took off in the 1970s, when people began writing their names on buildings all over the city. In the mid seventies it was sometimes hard to see out of a subway car window, because the trains were completely covered in paintings known as masterpieces.

Art galleries in New York began buying graffiti in the early seventies. But at the same time, John Lindsay, the then mayor (市长) of New York, declared (宣布) the first war on graffiti. By 1980s it became much harder to write on subway trains without being caught, and instead many of the graffiti artists began using roofs of buildings or cloth.

The debate over whether graffiti is art or vandalism (故意破坏公共财物罪) is still going on. Peter Vallone, New York city councilor (市议员), thinks that graffiti done with permission can be art, but if it is on someone else’s buildings it becomes a crime. On the other hand, Felix, a member of the Berlin-based group Reclaim Your City, says that artists are getting cities for the public back from advertisers, and that graffiti stands for freedom and makes cities livelier.

For years graffiti has help a few people gain international fame. Jean-Michel Basquiat began writing graffiti on the street in the 1970s before becoming a famous artist in the 1980s. Works by the British artist Banksy have been sold for over £100,000. Graffiti is now sometimes big business.