Can we learn to be happy? Experts say we have entered a mental health crisis as record numbers of children are referred to psychological services. Some are calling for 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
Palaeolithic - An early part of the Stone Age, when humans used basic stone implements.
Evolutionary - Relating to evolution, a process of gradual change that takes place over many generations, during which species of animals, plants, or insects slowly change some of their physical characteristics.
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.
Modernity - The state of being modern.
Depression - Low mood that affects someone's daily life, and can last for weeks or months.
Abundance - Having lots of things or a particular thing.
Indigenous - Ethnic groups who are the original or earliest-known inhabitants of an area or country: for example, Native Americans in the USA.
Privilege - Advantages or opportunities that certain people have that others do not.