In the 1966 science-fiction movie One Million Years B. C., the movie characters had a time travel and arrived in an ancient landscape inhabited by dinosaurs and early humans. The movie was low on science and high on fiction: by then dinosaurs were long dead and modern humans were millions of years away.

A more accurate picture of Earth’s inhabitants at the time is now being revealed. In research published in Nature, a team of scientists led by Anders Gotherstrom at the University of Stockholm, and Love Dalen at the Centre for Palaeogenetics (古遗传学), also in Sweden, describe sequencing (测序) DNA samples from mammoths (猛犸象) that lived and died in north-eastern Siberia around a million years ago.

The team’s work represents a new record, for their mammoth DNA is, by some half a million years, the oldest ever successfully reconstructed. Extracted (提取) from horses, bears and even Neanderthals and Denisovans, two close cousins of modern humans, such ancient DNA has proved an invaluable tool for investigating the past. Although fossils preserve the basic physical features of extinct animals, they are silent about many crucial details that even an incomplete genome (基因组) can help to fill in.

The trouble with DNA is that it breaks down after death. The more broken down it is, the harder it is to sequence. Scientists think that, after about 6m years, all that would be left would be individual base pairs (碱基对), the equivalent of trying to reconstruct a book from several letters. Under the right conditions, however, such as the extreme cold of Arctic permafrost (冻土层) this decay can be slowed.

Dr. Dalen and his colleagues were interested in three mammoth molars (臼齿) extracted in the 1970s from Siberian geological layers that suggested great age. Samples from each were sent to Dr. Dalen’s laboratory in 2017. Having checked they had not been contaminated by bacteria or the shaking hands of Paleontologists, the DNA were extracted, sequenced, and dated. Whereas DNA samples from a living animal can run to several hundreds of thousands of letters, the ancient mammoth samples yielded merely dozens of letter long. This is close to the limit of what is scientifically usable, says a biologist named Ludovic Orlando.

We human beings need to stay in touch with nature-many studies show how much better people feel when in sight of trees. Yet even more importantly，nature itself needs us to stay in touch. Many politicians and scientists have told us that we can "conquer" nature，but in reality nature will always be beyond our control---we do have the power to destroy it. The fate of all the animals and their habitats depends largely on our attitude towards them. Whether or not we ourselves survive depends on how well we look after the rest. For our sake as well as theirs，we need to consider it seriously.

But how can we care at all if we spend our lives indoors？Born in South London at the end of the Second World War，at least I knew what a sparrow was（they're rare now）and you couldn't put a spade into our tiny garden without cutting a worm in half. We knew，too，that milk comes from cows and that old men can grow amazing carrots on poor land. Ultra-urban（极度城市化）as we may have been，at least we were in touch.

"Now we have a generation who frankly are not in touch. So how can they care if the countryside is sold off to the highest bidders，and used to park helicopters，and our crops come free from Monsanto and our livestock live in factories？They will know no other way.

But if we settle for the ultra-urban life，if we allow all wilderness to be compromised and hand our farming over to industrial chemists then，quite simply，the world will fall apart--as it has been doing already. We have to rethink what agriculture is really for，and why conservation matters to us，as well as to other creatures. Changes of strategies begin with attitude and attitude begins with awareness.

On a dark night, 11-year-old Joe was playing hide-and-seek with his friends in the backyard when he thought he saw Magellan—a huge housecat. However, when the cat suddenly jumped on his head, Joe found it turned out a young cougar. He backed away from the animal, then turned and ran inside the house.

Cougar encounters like this one are becoming increasingly common in the U.S. Most people assume that’s because cougar populations are growing, or because the big cats are coming into closer contact with the expanding web of human suburbs. But Professor Robert Wielgus at Washington State University argues that poorly designed hunting policies might be causing an increase in cougar-human conflicts.

Wielgus’s research teams have been fitting the big cats with radio collars and monitoring their movements. They find that the cougar population is actually declining rapidly and almost no male cougars are over four years of age. And a study shows that the heavily hunted area has five times as many cougar complaints as the lightly hunted area—even though the density of cougars is about the same in both areas.

Wielgus suspects that hunting policies, which allow older males to be killed to keep cougar populations in check, were the culprit and teenage cougars in the heavily hunted area may be responsible for most of the trouble. To test his theory, he adds two more groups of cougars to the tracking program—one in a heavily hunted area and another in a comparable but lightly hunted area. He concludes that heavy hunting indeed almost wipes out older males and the population structure in the heavily hunted area shifts toward younger animals.

With these findings, Wielgus believes without adults to keep them under control, the disorderly teens are more likely to come into conflict with humans, farm animals and pets.

Wielgus’s ideas don’t sit well with everyone. “Hunting definitely does cause lots of teenage males to flow in, but I don’t yet see solid proof that they are more likely to cause trouble than older cats,” says the University of Montana’s Robinson. “In many cases, the new arrivals have been squeezed out of remote wilderness habitat and forced into areas where they are more likely to encounter humans. I think humans are primarily responsible for all the interaction you see. We’re moving into these areas where cougars and deer are,” according to Alldredge, a researcher at the Colorado Division of Wildlife.

We may not understand what makes 18-year-old males more likely than 48-year-old men to do dangerous things, Wielgus says, but we know that the world would be a different place, if teenagers were in charge.