YOUR QUESTIONS ANSWERED

1. Why do sweaty feet smell of cheese?

The same bacteria that is used to ripen many cheeses, including Munster, Limburger and Port-du-Salut, also lives on our skin and eats dead skin cells. It’s called 'Brevibacterium'; as it digests it gives off S-methyl thioesters, which smell cheesy. Another skin-munching bacterium is 'Staphylococcus epidermidis', which produces the cheesy, vinegary-smelling isovaleric acid. The final ingredient in this ‘socktail’ is 'Propionibacterium', which converts sweat into the sour-smelling propanoic acid. LV

2. How do aquatic snails breathe?

Most species of aquatic snail have a comb-like gill. The oldest groups have two gills but the majority have lost one, to make room inside their spiral shell. As snails moved to the land, they swapped gills for a primitive lung, called the pallial cavity. Some snail groups moved back to freshwater and a few reevolved external gills.

Others stay close to the surface and use a snorkel tube to gulp air now and again. Pond snails mostly breathe air but can flood their pallial cavity and use it as a basic gill when their pond freezes over. LV

3. Why did humans evolve a sense of humour?

A recent theory holds that humour evolved because it encourages us to perform the arduous task of fact-checking our assumptions about other people’s intentions and perspectives. By this account, mirth is the reward we get when we debunk one of our presumptions and see things suddenly in a new light – jokes are ‘super-normal stimuli’ that exploit this system. Once it evolved, humour became a social signal – we assume funny people are intelligent and friendly, and men and women alike prefer witty partners. On average, however, men tend to be more concerned that would-be partners will find their jokes funny, whereas women are more attracted to people who make them laugh. CJ

4. Why do dogs bury bones?

Wolves bury food that they can’t eat immediately. This keeps it safe from scavengers like crows and the cold ground helps to preserve it. Birds don’t have a good sense of smell so they find it harder to locate these buried caches than wolves do. Dogs retain this behaviour and will bury toys or bones – either because they are saving their leftovers, or just because they are bored.LV

5. Why do both fission and fusion release energy?

Nuclear fission involves splitting atomic nuclei, and is the process used in nuclear power stations. Fusion, as its name suggests, involves fusing nuclei and is the power source of the stars. While both fission and fusion release energy, the process and amount is very different. Fission exploits the instability of nuclei of heavy elements like uranium, which can be split using neutrons, producing fragments with a lower total mass. The difference appears as energy – courtesy of E=mc² – which is carried away by fast-moving neutrons. In contrast, fusion involves ramming together nuclei of light elements like hydrogen so violently they fuse together, producing fresh nuclei plus neutrons. Again, the lower mass of the fusion products is turned into energy via Einstein’s famous equation, but over 10 times the amount produced by fission for each gram of ‘fuel’. RM

6. Does sunshine really make us happier?

When it’s sunny, it seems like people are happier – we fill the parks and beaches, and radio stations start blasting out upbeat tunes. And yet, research has repeatedly failed to find any evidence that people who live in sunnier places enjoy more positive moods. A new, massive study published this year even brought into question the idea that a lack of sunshine can lead to seasonal affective disorder (SAD). Nearly 35,000 US adults completed a mood survey at different times of year and there was no evidence of more depression symptoms among those who completed the survey in winter. CJ

7. Do identical twins have identical genes?

They start with identical genes, because each is formed from a single fertilised egg that splits into two embryos. But from that moment onwards, their DNA begins diverging. The DNA replication mechanism introduces about one new mutation for every 100 million base pairs copied, per generation. There are around three billion base pairs in the human genome, so you would expect between 10 and 100 new mutations per person that occur early enough in embryonic development to be present in most cells in the body. Ordinary DNA tests won’t normally detect this because they only examine a short section of the DNA, in a region known to be highly variable between individuals. But if the entire genome were sequenced, these differences would show up. In France a case of multiple rape, in which identical twin brothers were both suspects, was solved in this way in 2012.

Your DNA also gets modified by epigenetic mechanisms such as DNA methylation. This changes the chemical structure of the DNA and affects how active certain genes are, based on diet and other lifestyle differences. So identical twins that have lived different lifestyles could also be genetically distinguished in this way. LV

8. Why does cold water take your breath away?

It’s called the cold shock response. When the cold receptors in your skin are all suddenly stimulated they cause an involuntary gasp and, for about a minute after that, hyperventilation. If you fall into chilly water, the cold shock response will kill you long before hypothermia does. Either that first gasping breath will fill your lungs with water (drowning you instantly), or the hyperventilation will make swimming almost impossible. In the UK, 67 per cent of drowning victims are strong swimmers, and over half of those are within 3m of the shore or the side of their boat when they drown. LV

9. Why are there two sexes?

Biologically speaking, the most important difference between the sexes is that females produce eggs that are much larger than the sperm of the male. Large eggs are an advantage because they provide more resources for the developing zygote. But making your eggs large means that you can’t produce so many of them, so another valid evolutionary strategy is to make lots of small, cheap sperm. Both of these strategies seem to be more effective than the compromise of producing a moderate number of middle-sized gametes, so evolution has gradually driven eggs and sperm in different directions. Once they’ve evolved to have different gametes, the sexes are also driven to evolve other differences. For males to be promiscuous, and females to be choosy, for example. LV

10. Could Earth capture an asteroid?

It is certainly possible but highly unlikely. Typically, asteroids are travelling far too fast for Earth’s gravity to make much of an impact on their trajectories. They normally have more than enough energy to escape Earth’s influence even if they approach very close. However, if they are of the right mass, are travelling at just the right speed, and manage to miss our planet by just the right amount, they could end up in a stable orbit around Earth. This capture process was probably how Mars got its two small moons, Phobos and Deimos. AG

11. Who really invented the light bulb?

The basic idea of using electricity to create light was first investigated over 200 years ago by the English chemist Humphrey Davy. He showed that when electric current flowed through wires, their resistance caused them to heat up to the point where they gave out light. But he also identified the key problem to creating the first practical ‘incandescent light’: finding a cheap material that both burned brightly, and lasted for many hours.

US inventor Thomas Edison is often credited with creating the solution in 1879: the carbon filament light bulb. Yet the British chemist Warren de La Rue had solved the scientific challenges nearly 40 years earlier. He used thin – and thus high-resistance – filaments to achieve the brightness, and delayed burnout by making them from high-melting-point metal sealed in a vacuum. His choice of pricey platinum for the filament and the difficulties of achieving a good vacuum made the result uneconomic, however. In 1878, another British chemist, Joseph Swan publicly demonstrated the first light based on commerciallyable carbon, but his use of relatively thick filaments still led to burnout. Edison's combination of thin carbon filament design with better vaccums made him the first to solve both the cientific and commercial challenges of light bulb design.

12. Are there any vegetarian spiders?

Just one. Out of around 40,000 spider species, 'Bagheera kiplingi' is the only spider known to have a herbivorous diet. It lives in Mexico and Costa Rica, and feeds mostly on protein nodules of the acacia tree. But even this spider sometimes eats ant larvae, so perhaps it is closer to the sort of vegetarian that doesn’t count prawns! LV

13. Why doesn’t Europa have any impact craters?

Europa is one of the smoothest objects in the Solar System. Although there are many surface features, including craters, these are few and far between. It is believed that Europa’s surface is a series of brittle tectonic ice plates moving on top of a warmer layer of convecting ice. Beneath that is probably a subterranean ocean of water. Recent observations have shown these icy tectonic plates moving about, creating ice plumes and ‘cryolavas’ in a mechanism akin to volcanism on Earth. This constant recycling of the surface material means that craters and other features don’t survive for very long. AG

14. If humans had wings, what would their wingspan be?

The extinct bird 'Argentavis magnificens' weighed about as much as an adult human and it had a wingspan of 7m – four times the average human arm span. This bird had lots of other adaptations to allow it to fly though, including the muscles to support these wings and flap them. Hang gliders, which allow humans to ‘fly’, are 9-10m across. LV

15. What causes recurring nightmares?

Approximately 2 to 5 per cent of the population suffers from recurring nightmares, and often the reason is that they have survived some kind of life-threatening situation, such as a car accident or a violent attack. Indeed, one study estimated that between 50 to 70 per cent of patients with post-traumatic stress disorder (PTSD) experience chronic nightmares. Other psychiatric conditions associated with an increased risk of experiencing frequent nightmares include schizophrenia, anxiety, and alcohol and drug abuse. Among people without a psychiatric diagnosis, a dream diary study from 2003 found that nightmares were experienced more often at times of stress. CJ

16. Why does heat have a shadow?

Thermal energy – the physicist’s term for heat – comes in various forms, including infrared radiation, which is part of the electromagnetic spectrum, like visible light. As such, this form of heat can be blocked by objects, creating a shadow. But the other forms of heat can still get to us via, for example, the motion of warm air known as convection. RM

17. Why doesn’t Earth’s atmosphere vanish into the vacuum of space?

While we can’t see them, the gas and vapour molecules making up the atmosphere all have mass, and as such all feel the gravitational pull of the Earth. They could still escape if they had enough energy – for example, if the Earth was closer to the Sun, and thus hotter. Fortunately, however, our planet has just the right mass and distance from the Sun to avoid that. RM

18. What is the bug bounty programme?

Some hackers love to break into computer systems to see what’s ‘under the hood’. It’s a big problem, so security has to constantly be improved to prevent intrusion. Several years ago, one company called Netscape Communications had a smart idea. They invited the hackers to try to break into the early versions of their software, and paid them if any issues or vulnerabilities were found. This became known as the bug bounty programme, and it is used by many software companies today to help improve their products. PB

19. If I dug down at 1m/s, what would kill me first?

EXHAUSTION
Let’s say you dig a 1x1m hole, which gives you enough room to wield a shovel. For each metre that you dig down, you have to remove a cubic metre of earth, weighing 1.6 tonnes. Even if you have some kind of bucket elevator so that you don’t need to lift the soil to the surface, you’re still shovelling almost 100 tonnes a minute.

HEAT
Maybe instead of manual shovelling, all the digging is taken care of by an automatic drilling machine that you stand on. But for every 40m that you descend, the temperature will rise by 1ºC. After 33 minutes you are 2km deep, and you die of heatstroke in the 50ºC air.

SUFFOCATION
Even if you have some kind of amazing cooling system, you are still in an ever-deepening hole with almost no fresh oxygen diffusing in through the narrow opening at the top. After a couple of hours of effectively rebreathing the same air, you’ll die of CO² poisoning at a depth of 7km. Or whenever your bottled air runs out.

20. What are supercomputers used for?

The best supercomputers fill rooms, cost millions, and are thousands of times faster than your computer at home. They are usually used for complex scientific problems involving lots of maths. They are used to predict the weather, model brains, or help predict the result of a nuclear explosion, for example. Some are used to test the strength of encryption (computer security) methods. They have been used to model the spread of swine flu, to predict climate change, and even to understand the Big Bang at the beginning of the Universe. But technology moves  A top-end desktop computer today calculates at the same speed as a supercomputer 10 years ago. PB

Written by Luis Villazon (LV), Christian Jarrett (CJ), Robert Matthews (RM), Alastair Gunn (AG) and Peter J Bentley (PB) in "BBC Focus", UK, edited by Emma Bayley, June 2016, excerpts pp. 83-93. Digitized, adapted and illustrated to be posted by Leopoldo Costa.