Why do humans kiss? You might think it is a universal trait, something that we all do. But when European explorers travelled the world, they met tribes that didn’t kiss. So is it a learnt response after all? It can be used as a greeting, a sign of reverence or supplication, but we will be talking about the romantic kiss: Face to face, lips to lips. We examine the biochemistry, psychology, anthropology and history of kissing. Where does it come from? Image: Two women kissing at a festival (Credit: AFP/Getty Images)

When many people struggle to maintain one relationship, why do some people enter into multiple simultaneous marriages? Lucy Ash speaks to polygamists around the world to find out why they were drawn to these complex arrangements and how they manage them. Lucy hears about rotas, hierarchies and curfews from the stars of a popular South African reality TV show about a businessman, his four wives and their ten children. The creator of a dating website in Gaza explains why many of his clients are looking for second or third wives. A woman who left her Mormon plural marriage in the American state of Utah tells how having to share her husband with a sister wife had a devastating impact on her mental health. What about polyandry – one woman marrying multiple men? Anthropologist Katie Starkweather explains why some societies have favoured it. (Photo: Models on wedding cake, Photo credit: Shutterstock)

Why do foreign migrants yearn to go home and what happens when they do? Some have had no choice, but others are influenced by nostalgia for their early lives. Or sometimes by disillusionment with their adopted country. When they go back, can the old country live up to their hopes and dreams? Shivaani hears emotional tales from those returning to Jamaica, Sierra Leone, India and Ghana.(Image: Empire Windrush, Credit: Getty Images)

Exams around the world: their significance in determining future prospects, their impact on mental health, and the debate surrounding their effectiveness. Experts discuss alternative assessment methods and the potential obsolescence of traditional exams. The influence of a gene on exam performance and the exploration of future assessment models are also covered.

We all experience negative emotions and find different ways to cope – maybe by exercising or by listening to music. But some people deliberately inflict pain on themselves as a way of managing how they feel. Why? Experts believe 15% of adolescents self-injure at least once, with some children as young as 9 using self-injury as a coping mechanism, albeit an unhealthy one. The behaviour can lead to feelings of guilt and distress; family and friends often don’t know how to help. Catherine Carr explores the impact self-harming has on those who do it and those close to them. She speaks to Matthew Nock, Professor of Psychology at Harvard University who explains the type of person most at risk of engaging in self-injury and the reasons why they use it to regulate their emotions.News reporter, Aidan Radnedge, describes why he began self-harming at university; and how his family and friends have given unstinting support throughout his road to recovery.Writer and editor, Janelle Harris, explains what it was like to discover that her daughter, Skylar, was self-harming aged 11. Now 18 and having graduated from high school, Skylar is no longer injuring herself and is looking forward to going to college next year. Dr Hayley van Zwanenberg, child and adolescent psychiatrist at the Priory Group of mental health hospitals and clinics in the UK, offers advice for parents on how to react if their children are self-harming – and offers alternative coping strategies for those struggling to deal with their feelings. If you’ve been affected by the issues in this programme, please visit the following websites for support and advice: Befrienders Worldwide: http://www.befrienders.org/about-self-harm Samaritans: http://www.samaritans.org/how-we-can-help-you/what-speak-us-about/signs-you-may-be-struggling-cope/helping-you-through-self LifeSIGNS: http://www.lifesigns.org.uk/ Talk Life: https://talklife.co/Presenter: Catherine Carr Producer: Sally Abrahams(Image: Sad beautiful girl, Credit: Wayhome studio/Shutterstock)

We all do it – sometimes. It can be embarrassing or just the way we organise our thoughts, a tool for remembering what is important. Sarah Outen, who spent four and a half years rowing, cycling and kayaking around the planet, says talking to herself, out loud, may have saved her life on more than one occasion. The actor, Steve Delaney, has created an alternate persona, Count Arthur Strong, whose most vivid character trait is talking to himself. We all have more wisdom than we dare to think we’ve got, according the psychotherapist Philippa Perry, it’s just a matter of speaking it. In this edition of the Why Factor, Matthew Sweet asks who are we talking to when we talk to ourselves.(Photo: A man talks to himself in the mirror. Credit to Getty Images)

Why take on a role where lots of people hate you for doing it? Dotun Adebayo talks to people whose daily life can include verbal and even physical abuse. They include an 18 year old referee in Manchester who has been head-butted and spat upon. He hears about electricity workers in Lagos in Nigeria who are regularly beaten up as they disconnect disgruntled customers. And the plus side of doing a thankless job from a debt collector in Jamaica and death row lawyers in Trinidad and Tobago and Guyana.(Photo: Man at top of pole fixing electric cables. Credit: Umar Shehu Elleman, BBC journalist)

Some people are numbers people – and some are not. One meltdown moment in the classroom is often all it takes to put people off maths for life. But, when you lose the ability to interrogate numbers, it makes it easier to be fooled by fancy figures. In this edition of The Why Factor, Timandra Harkness asks why people are intimidated by numbers. (Image: Frightened looking man surrounded by numbers. Credit: Wavebreakmedia/Shutterstock)

Why would anyone be a goth? What is the appeal of this dark and spooky subculture that embraces death, pain and sadness? Goths have been attacked, abused and are often misunderstood, but still choose to stand out – dramatically - from the crowd. Catherine Carr talks to goths about their music, their dress and their love of the darker side of life. Why has this scene that began in the UK in the late 1970s and has spread worldwide, adapted and endured? She hears from gothic vlogger, Black Friday, about how others react to her striking style and that of her goth husband, Matthius; she learns from Dr Catherine Spooner of Lancaster University about the role and influence of gothic literature in the goth scene and finds out from Professor Isabella Van Elferen of Kingston University, London about the transcendental power of goth music. Catherine talks to gothic blogger, La Carmina, about the extraordinary and extreme goth scene in Japan that includes body modifications; Dr Paul Hodkinson of Surrey University explains the enduring appeal of the subculture and why once a goth, you’re always a goth. And she meets Sylvia Lancaster, whose daughter Sophie, a goth, was murdered because of the way she looked. Presenter: Catherine Carr Producer: Sally Abrahams(Photo: Black Friday and husband Matthius. Credit: BBC Copyright)

How do you start your day? It’s a more complicated question than you think – and that’s because you don’t think about it very much. Quite a lot of what we do, we do every day. We create order by forming habits. From the way we brush our teeth to how we drive a car, ride a bike, or even tie our shoelaces – these are things we do every day without thinking. And it is a good thing we do because if we had to make multiple choices for every single simple activity our brains would just clog up. But there are good habits and bad habits. Ones that help us through the day and ones we cannot control. Shiulie Ghosh explains the difference between these behaviours and why, one way or another, we are all creatures of habit.(Photo: New Habits v Old Habits Credit: Shutterstock)