"Warm-bloodedness is one of the key factors that have enabled mammals to conquer the Earth, and to develop the most complex bodies in the animal kingdom. In this series, we will travel the world to discover just how varied and how astonishing mammals are."

“Midwinter, and the countryside is so still, it seems almost lifeless. But these trees and bushes and grasses around me are living organisms just like animals. And they have to face very much the same sort of problems as animals face throughout their lives if they're to survive. They have to fight one another, they have to compete for mates, they have to invade new territories. But the reason that we're seldom aware of these dramas is that plants of course live on a different time-scale.”

“For most people the idea of someone else telling them how many children they should have is simply unacceptable so when governments attempt to do just that it always causes controversy. In 1979 the Chinese government introduced its infamous one-child policy, changing family life in China forever. Families were encouraged to have fewer children. Those that didn't were fined. The policy was a direct response to the preceding decades of famine and starvation. It's still in place today. According to official figures, without the one-child policy, there'd be four hundred million more people in China, that's more than the entire population of the USA. Its unlikely that other governments could undertake such an extreme path without major civil opposition. In the 1970s the Indian government also sought to bring down its birthrate. To start with it took a less aggressive path, setting up festivals around the country where vasectomies were carried out for small incentives. m31s56”

“Birds were flying from continent to continent long before we were. They reached the coldest place on Earth, Antarctica, long before we did. They can survive in the hottest of deserts. Some can remain on the wing for years at a time. They can girdle the globe. Now, we have taken over the earth and the sea and the sky, but with skill and care and knowledge, we can ensure that there is still a place on Earth for birds in all their beauty and variety – if we want to … and surely, we should.”

“I support a group called the Optimum Population Trust which campaigns to reduce birth rates because I think, if we keep on growing, we're not only going to damage nature but we're likely to see even more inequality and human suffering. m4s08-m4s43”

“We have overfished 30% of fish stocks to critical levels. We cut down over 15 billion trees each year. By damming, polluting, and over-extracting rivers and lakes, we've reduced the size of freshwater populations by over 80%.”

“We must change our diet. The planet can’t support billions of meat-eaters.”