Can we learn to be happy? More and more children are coming forward for help with their mental health. Some say we need lessons in happiness.
NHS data exposes explosion of mental illness
Rich existence: People living in the indigenous Ibirama-La Klano area of Brazil be happier than those in wealthy cities. Glossary
Predators - Animals that prey on and eat other animals.
Stone Age - A prehistoric age in which stones were used as tools. It ended around 4,000BC, when metal began to be used instead.
Adapt - Change to fit a new situation.
Indigenous - Ethnic groups who are the original or earliest-known inhabitants of an area or country: for example, Native Americans in the USA.