Science of Sex, Smell and Pheromones

Researchers in the US have found that bad or shocking news really can break your heart. They found that after a trauma like this, people can suffer days-long surges in adrenalin and other stress hormones which "stun" the heart. This can even be mistaken for a heart attack. The researchers examined patients who came into hospital complaining of symptoms similar to those of a heart attack - chest pains, fluid in the lungs, shortness of breath and heart failure. But on closer inspection, these people - who were mainly older women - had no other signs of a heart problem. But all the patients had experienced some kind of severe emotional shock just before they got ill. For example, half had just learned of the death of a partner or relative. One person had been the victim of an armed robbery, while another had been the victim of a surprise party. And when doctors investigated further, they found that the patients had very high levels of stress hormones, particularly adrenalin and noradrenalin, in their blood. This was even higher than levels of these hormones found in genuine heart attack patients. The researchers also found high levels of another heart hormone, confusingly called brain natriuretic peptide. It's these stress hormones that can be toxic to the heart, say the researchers, effectively stunning it. Luckily, these broken hearts can be mended - using MRI scanning and other techniques, the doctors found that the damage caused by stress is temporary, usually lasting just weeks. So there's no need to cancel that surprise party just yet.

Chris - Your research is orientated towards the sense of smell and olfaction. What is a smell?

Peter - A smell is a chemical. The chemicals float around in the air around us and can tell us what is nearby. We have special receptors in the nose that can pick up these chemicals. This causes a response, which is then transmitted to our brain.

Chris - What about when there are lots of smells mixed up in the air? Your nose must get bombarded. How does the brain work out what it is smelling?

Peter - Coffee, for example, has around one hundred different odour components to it. When these go up someone's nose, lots of cells are activated. It's the pattern of these activated cells that the brain recognises as coffee odour. A slightly different pattern will show the difference between a normal coffee and an elaborate one.

Kat - I've noticed that food doesn't taste right when I have a cold. Is that related?

Peter - Despite what you would think, a lot of the flavour of food comes in through the nose. When you chew, chemicals are released into your mouth and some go up the back of your throat into your nose. Your tongue is not as refined at telling flavours apart, so your nose is an important part of tasting. When you have a cold, your nose gets blocked up and the chemicals from the food can't get through. This is why food can taste bland or different.

Chris - Why do dogs have such an acute sense of smell?

Peter - There are two ways in which a sense of smell can be better. One way is that the dog can be more sensitive and pick up smaller concentrations of a chemical, such as in a scent trail. The second way is to have more of the different types of receptors. This gives them a finer-grained ability, so they can tell things smell differently even when we might think they are same.

Chris - If you look at the brain of a dog, over a third of it is dedicated to smelling. This is in contrast to humans, which have sight as our main sense. Dogs really do live in a olfactory world.

Peter - Yes, and this is the same with most animals. Our sense of smell has actually been decreasing over evolutionary time. We have remnants of genes coding for these different receptors, but they don't work anymore. For that reason, they are called pseudogenes. Humans now have about 350 types of receptors. Rats might have about 1000 receptors picking up smells, which indicates the different smell worlds we live in.

Kat - I love the smell of my boyfriend's t-shirts. Does that mean that he's the man for me?

Peter - It could do. It's well known that people have different body odours, and it's these odours that dogs pick up on when trying to follow someone. It has also been suggested that people unrelated to you have particularly attractive body odours. Alternatively, when you get to know someone really well, you could just get to like everything about him, including the way he smells.

Chris - When women live in the same house, such as with groups of students, they often find their menstrual cycles start to synchronise. Why is this?

Graeme - We don't know for sure, but it might be a chemical from under the arms that can influence menstrual cycles. An experiment was carried out where chemicals from a woman in the early stage of her cycle were put on the upper lips of other women. This caused the other women's cycles to shorten. When the same experiment was performed using chemicals from a woman late in her cycle, the cycles of the women in the experiment seemed to lengthen.

Chris - Why would it be advantageous for women to have their periods at the same time?

Graeme - That's a good question but no-one really knows. If females were all to come and be receptive at one time, then it would mean that males are more likely to pair up with individual females and there'd be less likelihood of males having more than one female partner. Alternatively, it could have something to do with the possible rearing of the offspring. This is very difficult to see in terms of human biology. No-one really knows.

Chris - Part of your work is on social structure in insects and how chemicals like pheromones can change how different insects behave. Ants are a classic example of this.

Graeme - Yes they are. When you look inside an ant colony, you can see the queen and the ant workers. The workers are divided into castes: you might have foragers that go out and find food and you might have nurse ants that stay at home and look after the young. One of the things we can do is distinguish between the queen and the different types of workers by their chemicals.

The chemicals themselves don't make ants do different jobs. The roles each ant performs in the colony seems to depend on how old you are. Those that go outside the colony are going to be mature individuals. As workers are expensive to make, you want to get as much work out of them as possible. When they are young, it's best to give them jobs inside the colony and keep them safe. Only when they are older and more dispensable does it make more sense to send them out.

Lots of work has been done on bees. In a social insect colony, it's basically just a lot of women living together. The queen produces a chemical that controls the reproduction of all the other individuals by turning off their ovaries.

Chris - Are there analogous genes in people?

Graeme - No. It's a totally different social structure. Social insects are very specialised.

Chris - When you find an ant in your house, do you kill it or study it?

Graeme - I tend to study it, although it's not good if you find ants in your house.

Kat - Can you get rid of ant trails altogether so they stop coming in your house?

Graeme - No, not really. When an ant finds some food, it leads a chemical trail back to the nest for others to follow. While there's food there, the ants will keep on reinforcing the trail. Therefore it's very hard to get rid of them once they're there. The trails remain.

If you took the back end of a few ants and made a trail to send them back outside, you might end up getting rid of them! The trails are just made in chemical glands in back of the ant. As it drags its bottom along the floor, the compounds are released. Sometimes have a sting which almost acts like a nib. Once on surface, the compounds start to evaporate into the air. The antennae can then pick up these signals. Antennae are like ant noses.

Chris - How do they know which way is home?

Graeme - It's all about the angles at which the trails are being laid. When you leave the colony, you probably walk for a bit and then split off into two directions. Whenever they split, they choose an angle, usually about 51 degrees. This means that when the ants are walking away from home, they always find angles at 51 degrees. When walking back the other way, the angle is completely different. This allows them to know which way they're going.

There are various ways in which you can lose sense of smell. For instance, people can lose their sense of smell if they are allergic to something. These people can often regain it if the object they are allergic to is removed. In other people, events such as car accidents can cause a person to lose certain connections in their brains and stop being able to smell. It can sometimes come back after long period of time, but this usually depends on the type of accident the person was involved in.

Part of it might have been that pheromones were useful in the past when we didn't wash every day. It isn't clear whether by washing, we remove all these chemical cues. One of the main pheromone interactions is between men and women. No-one knows whether women are turned on by male pheromones or repulsed! Females may be repulsed at certain times of the month but attracted when it is particularly good to mate. Some research suggests that now many women are on the pill, they might be responding in a different way to pheromones, or even be desensitised.