A look at the man-made environment: the city. Over half of the world's population now lives in the urban jungle. The city is built to keep untamed nature out - but nature can't be pushed away. From bed bugs sucking blood at night to rats in our restaurants, many animals have adapted to a life in man's creation.

A look at the man-made environment: the city. Over half of the world's population now lives in the urban jungle. The city is built to keep untamed nature out - but nature can't be pushed away. From bed bugs sucking blood at night to rats in our restaurants, many animals have adapted to a life in man's creation.

Rivers provide the essentials of life: fresh food and fresh water. They act as natural highways and enable humans to live in just about every environment on Earth. Rivers are not to be taken for granted, however, as they freeze, flood, and sometimes dry up - disappearing entirely!

Rivers provide the essentials of life: fresh food and fresh water. They act as natural highways and enable humans to live in just about every environment on Earth. Rivers are not to be taken for granted, however, as they freeze, flood, and sometimes dry up - disappearing entirely!

Grasslands feed the world. Over thousands of years, humans have learned to grow grains on the grasslands and domesticate the creatures that live there, propelling our population to almost seven billion people in the process.

Grasslands feed the world. Over thousands of years, humans have learned to grow grains on the grasslands and domesticate the creatures that live there, propelling our population to almost seven billion people in the process.

From lush cloud forests to bare summits, many people make their homes in the extreme altitudes of the world's mountain ranges. Explore the extraordinary ways life is sustained in this world of thin air and few resources.

From lush cloud forests to bare summits, many people make their homes in the extreme altitudes of the world's mountain ranges. Explore the extraordinary ways life is sustained in this world of thin air and few resources.

The rainforest is home to more species of plants and animals than any other habitat on the planet. For the humans who call this environment home, life requires skill, ingenuity, and sheer bravery.

The rainforest is home to more species of plants and animals than any other habitat on the planet. For the humans who call this environment home, life requires skill, ingenuity, and sheer bravery.

Welcome to the Arctic: months of darkness, frigid temperatures, little food to be found or grown. Despite this, four million people live their lives in this environment. Meet them and witness their remarkable tales of survival in the world's harshest climate.

Welcome to the Arctic: months of darkness, frigid temperatures, little food to be found or grown. Despite this, four million people live their lives in this environment. Meet them and witness their remarkable tales of survival in the world's harshest climate.

While man can survive for weeks without food, he can survive mere days without water. Despite this, millions of people live in parched desert environments around the world. Discover the enormous challenges presented to man in the driest corners of the earth, and marvel at the ingenious solutions he has come up with to make life sustainable.

While man can survive for weeks without food, he can survive mere days without water. Despite this, millions of people live in parched desert environments around the world. Discover the enormous challenges presented to man in the driest corners of the earth, and marvel at the ingenious solutions he has come up with to make life sustainable.

As an air-breathing animal, man is ill-suited to living in watery environments. Nonetheless, people in certain cultures have found ways to live an almost aquatic life in order to exploit the vast riches of the sea.

As an air-breathing animal, man is ill-suited to living in watery environments. Nonetheless, people in certain cultures have found ways to live an almost aquatic life in order to exploit the vast riches of the sea.