Human sexuality comes in many forms, from exclusively heterosexual to exclusively homosexual. But seeing as homosexuality creates apparent reproductive and evolutionary disadvantages, listener Ahmed from Oslo wants to know: why are some people gay?

CrowdScience presenter Caroline Steel examines what science can - and can't - tell us about the role of nature, nurture and evolution in human sexual attraction. She asks a geneticist what we know of the oft-debated 'gay gene', as well as looking into why homosexual men on average have more older brothers than heterosexual men.

Caroline looks into the role of nurture with a developmental psychologist to answer a question from a CrowdScience listener from Myanmar. He wonders if the distant relationship he has with his own father has impacted his own feelings of attraction.

She also learns about research into a group of people in Samoa who may shed light on the benefits of traditionally non-reproductive relationships for communities as a whole.

Presented by Caroline Steel

Contributors:

(Photo credit: Ahmed Umar)

There are over 30,000 species of fish – that’s more than all the species of amphibians, reptiles, birds and mammals combined. But despite the sheer diversity of life on Earth, we still tend to think of all fish in roughly the same way: with an oblong scaley body, a tail and pairs of fins. Why? And is that really the case?

Crowdscience listener and pet fish-owner Lauria asked us to dive into the depths of this aquatic world to investigate why fish are shaped the way they are. Do we just think that fish are all the same because we are land-dwelling?

Presenter Anand Jagatia makes a splash exploring the fascinating story of fish evolution, how they came to be such a different shape from mammals and even how some mammals have evolved to be more like fish.

Produced by Hannah Fisher and presented by Anand Jagatia for the BBC World Service.

Contributors:

Image: School of fish in shape of fish. Credit: Getty Images

CrowdScience listener Alix has a burning question - what’s actually happening inside the flames of a campfire to make it glow? And why do some materials burn easily, while others refuse to light at all?

To find out, Alex Lathbridge travels to the Fire Research Centre at the University of Edinburgh to (safely) set various things ablaze. He learns about the fundamentals of fire and why things react differently to heat. He then heads to archives of the Royal Institution of London, to see an invention from the 19th century that can stop a fireball in its tracks: the miner’s safety lamp, which saved countless lives. And he speaks to a chemist about the science of flame retardants, and how even though they can make products less flammable, they may also have unintended consequences.

Presenter: Alex Lathbridge

Contributors:

Laugh and the world laughs with you, or so you might think. But watch any good comedian on TV by yourself and chances are you’ll laugh a lot less than if you were sat in a lively comedy crowd watching the same comedian in the flesh.

But why is that? Do people from different cultures and corners of the world all laugh at the same things? These are questions raised by CrowdScience listener Samuel in Ghana who wonders why he’s always cracking up more easily than those around him. Presenter Caroline Steel digs into whether it’s our personality, the people around us, or the atmosphere of the room that determines how much we giggle, following neuroscience and psychology on a global trail in search of a good laugh.

Producer: Richard Walker

[Image: Two Women laughing. Credit: Getty Images]

Mathematics and our ability to describe the world in terms of number, shape and measurement may feel like a uniquely human ability. But is it really? Listener Mamadu from Sierra Leone wants to know: can animals count too?

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Sounds:

Presenter: Marnie Chesterton

When CrowdScience listener Eric spotted a few gnats flying around on a milder day in mid-winter it really surprised him - Eric had assumed they just died out with the colder weather. It got him wondering where the insects had come from, how they had survived the previous cold snap and what the implications of climate change might be for insect over-wintering behaviour? So he asked CrowdScience to do some bug investigation.

CrowdScience presenter Marnie Chesterton takes up the challenge and heads out into the British countryside – currently teeming with buzzes and eight legged tiny beasties - to learn about the quite amazing array of tactics these small creatures use to survive the arduous days of cold.

She hears how some insects change their chemical structure to enhance their frost resistance whist others hanker down in warmer microclimates or rely on their community and food stocks to keep them warm.

But cold isn’t the only climatic change insects have to endure, in the tropics the seasons tend to fluctuate more around wet and dry so what happens then? Marnie talks with a Kenyan aquatic insect expert who describes how mosquitoes utilise the rains and shares his worry climate change could have a big impact on insect populations.

Contributors:

Presenter: Marnie Chesterton

[Image: Butterfly in winter resting on snow covered branch. Credit: Getty Images]

Have you ever wondered why waterfalls appear white when still water is transparent? Why clouds, or snow, appear white when they too are essentially just water molecules in different states? What makes something white, opaque or transparent? These are the questions CrowdScience listener Gerardo has been pondering ever since taking in the beauty of fallen water on a hiking trail in his home of Cantabria, Northern Spain. Presenter Marnie Chesterton, sets off on a quest to find out the answers to all of those questions and more. What even is white? Is it a colour, the absence of colour or all the colours of the rainbow combined? Is black really the opposite of white? And what colours do we mix to make white or black paint?

Image: White paint in pots and a paintbrush. Credit: Getty Images

Imagine waking up to the smell of freshly baked bread. Doesn’t it make your mouth water? Now imagine the smell of a fish market on a warm day… still feeling hungry? CrowdScience listener Thanh from Vietnam is intrigued by the effects of smell on our appetite, and wants to know whether certain aromas can make us feel more full than others. Never averse to a food-based challenge, presenter Anand Jagatia takes us on a journey from the nose to the brain, where we find out what exactly happens when we get a whiff of various foods. He discovers how the digestive system prepares for a meal and the extent to which our stomach has a say in whether or not we want to eat, based on how appetizing the smells are around us. Anand also explores our cultural differences. In some parts of the world a stinky Limburger cheese is considered a delicacy, while in other places it could make people lose their lunch. We’ll find out why some of us get triggered in different ways than others.

From dumping raw sewage into rivers to littering the streets with our trash, humans don’t have a great track record when it comes to dealing with our waste. It’s something that CrowdScience listener and civil engineer Marc has noticed: he wonders if humans are particularly prone to messing up our surroundings, while other species are instinctively more hygienic and well-organised.

Are we, by nature, really less clean and tidy than other animals? Farming and technology have allowed us to live more densely and generate more rubbish - maybe our cleaning instincts just aren’t up to the vast quantities of waste we spew out? CrowdScience digs into the past to see if early human rubbish heaps can turn up any answers. We follow a sewer down to the River Thames to hear about The Great Stink of Victorian London; turn to ants for housekeeping inspiration; and find out how to raise hygiene standards by tapping into our feelings of disgust and our desire to follow rules.

Presented by Marnie Chesterton and produced by Cathy Edwards for the BBC World Service.

[Image: Man on beach with rubbish. Credit: Getty Images]

You have probably experienced an ‘earworm’ - a catchy bit of music that plays round and round in your head and won’t go away – at least for a short while. But why did it pop up in the first place and how did it get stuck?

CrowdScience listener Ryota in Japan wants us to dig into earworms, so presenter Datshiane Navanayagam bravely puts on her headphones to immerse herself in the world of sounds that stick. She meets with a composer of children’s songs as well as music psychologists to find out if there is a special formula to creating catchy songs and probes if this musical brain quirk serves any useful purpose. Datshiane then explores whether some people are more prone to catching earworms than others. Finally, for those who find this phenomenon disturbing - she asks is there a good way of getting rid of them?

Come join us down the audio wormhole - disclaimer - the BBC is not responsible for any annoying earworms caused by this broadcast.

Presented by Datshiane Navanayagam and produced by Melanie Brown

Interviewees:

[Image: Audio Cassette. Credit: Getty Images