According to the United Nations Food and Agriculture Organisation, 800 million people are going to bed hungry every night, but 2 billion people in the world are malnourished. Farmers across the globe produce enough food to feed 10 billion people, yet there are only 7.6 billion of us.

We know there is enough food to go around, but filling tummies is only the start – we also need a varied diet. CrowdScience visits Nairobi during GGIAR Science Week, a hub for agricultural scientists. They are meeting to discuss the changes needed to get the right crops into the soil and the right food on the plates of those who need it.

Presenters Anand Jagatia and Alex Lathbridge are joined by a live audience and a panel of experts Lindiwe Sibanda, Sieglinde Snapp and Alex Awiti. Together they explore questions from our listeners in Kenya and around the world: whether we can restore natural habitats whilst promoting food security; why human waste isn’t used more commonly as a fertiliser; and what impact empowering women in agriculture will have on our ability to feed the world.

Recorded at CGIAR Science Week at the UN headquarters in Nairobi.

Image: Drone view of tractor ploughing a field

CrowdScience listener Sid is running late, and he’s turning to science to find an excuse. He and his partner Steffi in Singapore have very different attitudes to timekeeping. They wonder if this is down to their different cultural upbringings, or if they just had very different brains to start with.

Presenter Chhavi Sachdev puts her own time perception skills to the test to try to understand how subjective our sense of time can be. And we discover how the language we grow up speaking can influence the way we think about punctuality.

Presenter: Chhavi Sachdev

What would you discover inside the stomach of a sea lion? CrowdScience listener Robyn found out first-hand when she volunteered at her local museum in Adelaide, Australia. The team dissecting the specimen removed around 30 rocks from the animal’s stomach, and Robyn wants the Crowdscience team to find out how and why they got there.

Presenter Anand Jagatia uncovers a whole world of rock-munching creatures, from ostriches to ichthyosaurs. In search of answers we investigate Canadian sea lion research, and rummage through the vaults at the Natural History Museum in Bamberg, Germany.

Presented by Anand Jagatia

Image: Australian Sea Lion (Neophoca cinerea), Hopkins Island, South Australia

On the banks of the St Lawrence River in Quebec stands a 100-year-old lighthouse. While initially built to help boats navigate one of Canada’s most difficult waterways, the Point-de-Père site now also holds a different responsibility: it is a key reference for measuring sea levels around the entire North America continent.

But this is all set to change. With the development of new satellite technology, the tricky task of measuring sea levels is being updated - which could mean mountains around North America get brand new official heights.

In this episode we revisit a question from CrowdScience listener Beth, who wondered about the elevation signs she saw scattered along a mountainous road, indicating how high above sea level she was. As sea levels rise, will all the elevation signs need repainting? And how do you measure sea level, anyway?

The height of an enormous pile of rock like Ben Nevis, or Mount Everest feels unchangeable. But we measure them relative to the nearest patch of sea, which is where our story becomes complicated. Unlike water in a bath, sea level is not equal around the world. In fact, nothing on earth - not the sea, the shore or the mountains - is stable or constant, so the question of what you measure from and to becomes incredibly tricky. But that hasn’t stopped scientists risking life and fingers to use an ever-evolving array of technologies to find answers.

Join host Marnie Chesterton as she dives into the mechanics of the latest sea level technology, and how it could make a big difference to understanding our unpredictable world.

Presenter: Marnie Chesterton

(Image: Elevation Sign Post, Rocky Mountain National Park. Credit: Stephanie Beverungen via Getty Images.)

Host Anand Jagatia tackles gravity - a fundamental force of the universe yet also an everyday mystery that has baffled several listeners. Can you outrun it? Or at least use it to get fitter? If it varies, does that mean that you weigh less, depending on where on earth you stand? And if it’s the force of attraction between any objects with mass, are you technically more attractive after eating a massive cake?

Professor Claudia de Rham from Imperial College London explains the basics of gravity, while we discover the best place on earth to weight ourselves, with Professor Paddy Regan from Surrey University and NPL Fellow in Nuclear and Radiation Science and Metrology.

Anand takes a very fast spin on a special chair to experience extra gravity, thanks to Professor Floris Wuyts from the University of Antwerp, Kings College London and Minister of Science of Asgardia.

And finally, we talk to an expert lined up at the other end of a hypothetical hole through the earth: Professor Richard Easther from the University of Auckland, New Zealand. What would happen if we fell straight through the earth?

CrowdScience finds gravity a force to be reckoned with.

Presenter: Anand Jagatia

Are food allergies higher in the West than the East? UK-based listener Jude wants to know the answer. Her daughter-in-law Min didn’t know anyone with food allergies when she was growing up in South Korea and thinks that they’re not so common there.

Host Alex Lathbridge investigates. Along the way, he finds out what makes us sensitive to food allergies and how much that depends on our environment. He volunteers to have an allergy test, learns what triggers food allergies and tries to discover what lies behind their increase around the world.

Alex talks to some of the leading experts on food allergies in search for an answer to our listener’s question: Paul Turner breaks down what happens in our bodies when we have an allergic reaction; Jennifer Koplin explains why Australia tops the league table for food allergies and Michael Levin reveals what he found out in his ground-breaking research in South Africa comparing urban and rural populations. We also hear from Hana Ayoob, who grew up in Singapore and the UK, who describes what it’s like to suffer from multiple food allergies and describes the difference in cultural attitudes. Finally, we turn to Sooyoung Lee in South Korea to see if our listeners are right about the difference in rates for food allergies between East and West.

Presenter: Alex Lathbridge

(Image: Young Asian father with cute little daughter grocery shopping for dairy products in supermarket Credit: d3sign via Getty Images)

CrowdScience listener Alina is in a relationship with a polyamorous partner and is very happy with this arrangement, which got her thinking – why is monogamy so often the norm in human societies?

Presenter Caroline Steel goes on an anthropological odyssey to figure out where this drive to find a single partner - and stick with them - comes from.

What can science tell us about how human relationships developed, and whether having one or many partners is more 'natural'?

Evolutionary biologist Kit Opie of the University of Bristol joins us at London Zoo to help us understand the mating systems of our closest primate relatives.

To find out how polygamy developed in some parts of the world we speak to anthropologist Katie Starkweather of the University of Illinois Chicago.

And we learn about the chemistry of bonding from Sarah Blumenthal at Emory University, who explains how the brains of prairie voles may give us clue about the neurochemicals which shape human relationships.

Presenter: Caroline Steel

(Image: Dancing wedding cake figurines Credit: Peter Dazeley via Getty Images)

The wetness of water seems blindingly obvious - but dive into the science and things aren’t so clear.

CrowdScience listeners Rachel and Callum were washing their hands one day and it got them thinking about wetness. Why does water feel the way it does? And what makes a liquid wet?

To find out, presenter Anand Jagatia takes a closer look at the behaviour of liquids with materials scientist Mark Miodownik, and finds out why they might not be as wet as we think.

We learn what’s really behind the sensation of feeling something wet on your skin, with the help of physiologist Davide Filingeri and PhD student Jade Ward.

And we turn to a philosopher, Vanessa Seifert, and a chemist, Tim Neudecker, to puzzle out exactly how many water molecules you need before the property of wetness emerges.

Presenter: Anand Jagatia

(Image: A photo of a droplet falling into a body of water Credit: Flaviu Cernea / 500pxvia Getty Images)

It’s citrus season in the northern hemisphere, and fruit trees are bursting with oranges and lemons. But CrowdScience listener Jonathan wants to know what happened to the tangerines he ate as a child in the 1960s? He remembers a fruit that was juicy, sweet and full of pips, found each Christmas at the bottom of his stocking. Tangerines today, he thinks, just don't compare.

Crowdscience tries to track down this elusive fruit. Presenter Anand Jagatia traces the tangerine's origins back to Ancient China, as botanist David Mabberley explains that the name ‘tangerine’ comes from a fruit that made its way from Asia, to Africa and the Moroccan port of Tangier, before arriving in the US in the early 1800s. Professor Tracy Kahn from UC Riverside tells us about the hybridisation process that goes into breeding modern tangerines, but says that while the season for these fruits has been dramatically extended, there’s a cost in terms of diversity and flavour.

Who better to help us track down this missing mandarin than a fruit detective? Well, that’s one of pomologist David Karp’s other job titles, and he reveals exactly which cultivar we might be looking for: the Dancy. So where can we find one? Over on Friend’s Ranches in Ojai, California, Emily Ayala shows us two trees planted by her late grandfather, and explains that nothing grown since really matches its unique flavour.

So what will listener Jonathan think when we send him a box?

Presenter: Anand Jagatia

(Image: Citrus oranges grow on tree, Hong Kong Credit: CHUNYIP WONG via Getty Images)

Vermillion red, vibrant orange, golden yellows, even violet – we're enchanted by the colours that make up a stunning sunset or sunrise. CrowdScience listener Paulina, a lighting designer from Chile, often uses the sunsets she sees from her balcony as inspiration for her designs. And during the day and night, the sky can be all sorts of shades of blue. But Paulina wonders why, in the colour palette of the sky, she never sees any green.

CrowdScience gazes skywards to investigate. Presenter Caroline Steel travels to the Arctic Circle to meet atmospheric physicist Katie Herlingshaw. Katie explains why we usually see the sky as blue, and what makes it transform into fiery reds and oranges at sunrise and sunset. We also peer into the science of perception, as neuroscientist Bevil Conway tells us what’s going on in our eyes (and brains) to make the colours we see in the sky.

But there are some rare occasions when the sky can appear to be green, such as in a rainbow or a green flash at sunset. And then there is the spellbinding green glow of the aurora - the Northern and Southern Lights. We visit the northernmost aurora observatory in the world to try to understand this phenomenon. Are green skies more common than we think?

Presenter: Caroline Steel

(Photo: View of sunset in Santiago, Chile. Photo montage courtesy of Paulina Villalobos)