Rules of Attraction: The Science of Sex

16 February 2016

The Naked Scientists have turned the lights down low for a stimulating odyssey through the science of dating and romance, including; which chat-up lines are most likely to get you talking, what statistics can tell us about our sex lives and lessons in love from the animal kingdom.

In this episode

00:49 - Why have sex?

Why does it take "two to tango" when you need to make babies?

Why have sex?
with Professor Laurence Hurst, University of Bath

For most animals, many plants and some fungus, sex is vital if you want to Graffiti sperm reproduce. But why does it take two to tango? Wouldn't it just be easier, and more efficient, if you could reproduce on your own? This is something of a puzzler to biologists, as Professor of Evolutionary Genetics at the University of Bath, Laurence Hurst explained to Georgia Mills...

Laurence - If you ask the question "why should any organism have sex?" many people's first response is "well you need it to reproduce don't you?"  And that is true, but when you're thinking about natural selection you also have to think - well what would the alternative be.  And the alternative is what we call asexuality, in that what happens is a female reproduces without the aid of a male and just makes all female progeny. 

Georgia - Key to Darwin's theory of natural selection is survival of the fittest.  If you were slightly worse at doing something like reproducing, you're going to get outcompeted and booted from the evolutionary gene pool.  So when it comes to the two strategies for making babies (sexual and asexual) it seems a no brainer.  In asexual you can do it on your own as a strong independent organism and all of your offspring will be able to too.  For sexual reproduction, you need to actually go out and find a partner and, if you manage to, your offspring are going to be 50/50 male and female so, only half of them will be able to make their own babies.  If it's a game of numbers, sooner or later team asexual should win - right?

Laurence - This nicely captures the central dilemma of the problem of the evolution of sex which is, actually, at first sight it looks as though it's hugely disadvantageous.  So this isn't a small cost that sexual females are suffering, it is a massive cost the sexual females are suffering, but, in the longer term, we see there must be some massive advantage therefore to having sex because it must be able to overcome this immediate disadvantage that you have simply in terms of number of progeny.

Georgia - I was going to say -  do we have any idea of why we're wasting so much time with this?

Laurence - Yes well, as you can imagine, because at first sight this is such an incredible waste of time, at least for females, and so the ideas of largely being dominated by thoughts on two sides.  One is that sex might be a very good strategy to getting rid of bad mutations, and the other is that it's a really good strategy of enabling the spread of adaptive mutations, or advantageous mutations.  But, what both of these have in common is the idea that what is really good about sex is that it generates variety.

Georgia -   When asexual animal make babies, they are essentially clones so, if mummy's bad at maths, all her offspring are bad at maths.  When you reproduce sexually though, you jumble up your DNA with someone else's and this creates variation.  Your children are different from you, and from each other.  So, a couple might be bad at maths but a couple might be very good, especially if you partner was.  This variation is kind of like keeping your eggs in different baskets, and this is a very good idea, especially because we are constantly at war with our parasites.

Laurence - Whatever sort of organism you are, you're always going to have a problem with parasites, and parasites like aids virus, worms, etc; these parasites have a typically reproductive cycle that is faster than ours so they can evolve to us faster than we can evolve to them.  Under these sorts of context, then it actually pays to be sexual because you're trying to get a new set of resistance strategies.  So we think that one of the great advantages of being sexual is that, indeed, it provides some resilience of my progeny to infection.  And some recent work, for example, has shown that, rather nicely, some organisms adjust the amount of sex they have.  They adjust that dependent upon their parasite status; if they're loaded with parasites, if the bug thinks it's got a parasite it actually has more sex than if it thinks it hasn't got a parasite.

05:27 - Animal attraction

Find out how they do it on the discovery channel, with a journey through the dating habits of the animal kingdom.

Animal attraction
with Max Gray, University of Cambridge

If you look across the world, at the birds and the bees and the flowers and the Bugs sextrees, almost all of it is geared towards sex. And just as animals have evolved many ways of moving and finding food, there is also a huge amount of variation in the way animals mate. Zoologist Max Gray took Khalil Thirlaway through dating in the animal kingdom... 

Max - Mating is the single most important that any animal is going to do because it's all about passing on your genes to the next generation, making more of your species which is what life is all about.   So animals need to be very good at it and so there's a huge amount of pressure - evolutionary pressure - selection if you will towards how mating systems work, and there's a huge variety in any number of different species that you can think of.

Khalil - So are there any general rules of thumb?

Max - Yes, there are a few.  The main one is that the mating cost is different for males and females - for females, it's more expensive.  This ultimately comes from the fact that an egg is much bigger than a sperm and when you get into more complicated breeding systems - you know birds laying eggs - an egg costs physically and energetically costs more than creating sperm.  And if you think about mammalian pregnancy, the whole process of pregnancy is far more energetically demanding than creating and ejaculating some sperm.

Khalil - So it sounds like being female is a bit of a short straw in many ways?

Max - It can be in some cases but in other cases it's definitely better to be female than it is to be male. A favourite example for valentine's day - since St Valentine was the patron saint of beekeeping as well as love - is in honey bees, the queen goes out on her mating flights and mates with a number of males and then, once she's done, she goes back and breeds and forms a colony.  But all the males, after they breed with her as part of the mating process, when they leave, when they disentangle themselves from the queen, their phallus is ripped from them and then they die slowly afterwards.  So it's definitely better to be a female bee...

Khalil - Ouch...

Max - Another good example is the Australian redback spider where you have again, the male and female start mating, everything is going alright but then the male will do a somersault almost, will flip himself over the female into the female's mouth - she'll you know, think this is delicious and start having a nice snack.  Will eat the male's body but, what's left behind is that his genitalia is left behind and will continue doing its business on its own - so to speak.  By sacrificing himself in this manner the male is more likely to successfully father some offspring.

Khalil - That is some serious dedication.  It sounds like a bit of a freeforall?

Max - In some senses it is.  I mean, broadly speaking, there a huge number of examples in any different number of cases that you can imagine but, in any species or in a family of species, mating tends to work in roughly the same way, so you can categorise these types of mating systems. A very common one in many species is called polygeny, so this is where one male will have sexual interaction with many females.  The dominant male who is the highest quality male will attract numerous females that he will kind of monopolise in a harem.  So this is what happens with a pride of lions and with many other species as well, but even that's not that simple because there are some species where this happens, at least on the face of it.  An example of this is cuttlefish - so you have one dominant male cuttlefish that monopolises all his lady cuttlefish but the less dominant males, of whom there are many, will kind of think but they still want to breed, they will still attempt to breed.  And if they come in as males and they get chased off by the dominant male, and that doesn't work,  So what some of them do is, because they're a little bit smaller and they're cuttlefish and they can change their colour, they will pretend to be female - they will adopt the colouration of females and sneak in so they get to be close to all the other females because they look like one and the male won't notice and then, while he's looking the other way, they will sneakily mate and get away with it that way.

Khalil - On the subject of mating systems, what about monogamy? You often here, for example, swans mating for life?

Max - You do yes.  It's quite commonly said that a lot of birds mate for life.  Another example is penguins.  In penguins it's not actually as simple as that and what seems to be monogamous, broadly speaking is but only on for one season at a time.  You get this thing called" seasonal monogamy" where penguins will mate dedicatedly with one individual until that chick is reared and an adult in it's own right.  And I think the statistic is only something like 15% of partners then reunite the following year in that specific pair. Swans are another example, as you mentioned, that is often claimed to be monogamous and they do tend to stay together for more than one year at a time - so called life mating.  But even then, it's not truly monogamous because if you do some genetic testing on all the eggs or the chicks after they hatch, you find there's still quite a high percentage of those chicks that are fathered by males that are other than the one that their mother was paired with.  And this seems to happen in almost any species that people have done that analysis of, that people claim is monogamous.

11:34 - Top science dating tips

Top psychology dating tips on how to find the one, and how to try and make sure they like you back?

Top science dating tips
with Professor Viren Swami, Anglia Ruskin University

When you're dating, what exactly makes you attracted to people, and how do you make sure they like you back? There's a wealth of information from pickup artists out there, but the science often says something a little different. Viren Swami is a psychologist from Anglia Ruskin University, and he joined Georgia Mills to give her some top science dating tips, and to go through what actually makes us attracted to people...

Viren - I suppose the first thing is that, if you are physically attractive, you'll receive a sort of premium in terms of dating.  So attractive people tend to get asked out on dates more often, they also tend to have sex more often and, if you're female, you probably have more orgasms during sex.

Georgia - Ah, that's not fair!

Viren - Well the idea is that if you're with someone who is physically attractive, your partner is more likely to make an effort with you in bed.

Georgia - Wow!  Why is good looking so important then?

Viren - Why it is that seeing someone attractive is rewarding in some way.  It activates a part of the brain that is also activated when we get any kind of reward, like drugs or money.  So it's possible that seeing someone attractive is rewarding and, if that's the case, then we want to see them more often.  The other possibility is that most human beings have a stereotype about what attractive people are like.  We tend to think that attractive people are more popular, more sociable, healthier, and we have all kinds of weird thoughts about these attractive people.  So it probably makes sense that if these thoughts are at least partially based in reality then we want to be with attractive people.

Georgia - Is attractiveness just a bonus in your dating life?

Viren - No, it's a bonus in all kinds of spheres.  So, in occupational settings people who are attractive tend to get hired more often, they tend to get fired less often, they get a higher starting wage, they make more money over the course of their lifetime.  In other settings, university students get a higher grade if they're attractive - I could keep going.

Georgia - This is not cheering me up this Valentine's day but, I suppose, it's not that surprising.  So what other things have you found - what about personality?

Viren - Well, lots of surveys have been conducted where you simply ask people what they look for in a potential partner and there are three main categories.  So the three categories tend to be physical appearance, and secondly possibly things like status and reputation.  But usually, the most important criteria that most people are looking for are things to do with niceness.  We like nice people, we like people who are loyal, have a good sense of humour, who are faithful, and so on.  And this is true of both women and men so, both women and men say they would like a partner who has all these qualities.  One of the things people maybe don't think about very often is the effects of proximity.  We like people who are nearby, in general, and we we tend not to have too many relationships with people who are further away, but when you ask people about proximity, it maybe doesn't figure so much in their thoughts a potential partner.  We don't tend to think like I'm looking for someone who's nearby, but that's actually what tends to happen.

Georgia - What about 'playing hard to get' - is this a good idea?  I've heard a lot of people suggest this as a sort of tip for getting a man?

Viren - Well, the science suggests that it doesn't work, and it doesn't work because it contravenes the theory of reciprocity.  The theory of reciprocity simply predicts that we like people who like us, so showing someone that you like them, in theory, should result in them liking you in return.  Playing hard to get contravenes that; it shows that you dislike someone or you're too difficult to get.  The idea from science is that, actually, there is a separate thing you can do which is to play selectively hard to get.  And playing selectively hard to get simply gives the impression that to every possible suitor in the world you are hard to get but to that one special person that you like - you are very easy to get.

Georgia - So just be mean to everyone else except the one you want?

Viren - Exactly.

Georgia - Now speaking of dating tips.  We spoke a little bit yesterday about some good and bad chat up lines and you fed me some lines, which science says should be good or should be bad, and I went out to Cambridge Brew House, with some help, on a little social experiment to try some of these lines. So the first one you gave me is "if you could have any topping on a pizza what would it be?"  So let's hear how we got on...

Robbie - I've just got a question for you? If you could have any topping on a pizza right, anything you want, what would you have?  Anything on a pizza?

Girl - On a pizza - bacon.

Robbie - Bacon.  Why would you have bacon?

Girl - I don't know.  I like bacon for my pizza.

Robbie - You like bacon? I think I'll have mushrooms - I'm a mushroom kinda guy.

Georgia - That was willing participant Robbie Bennett you heard there trying your line, and it did work pretty well.  They ended up talking together for ages.  So what actually makes this a good line?

Viren - It goes back to the theory of reciprocity. Reciprocity simply predicts that when you ask an open-ended question, you're much more likely to get a reply from that person.  But that particular question also forces the other individual into a norm of conversation.  The kind of tendency is to ask the other person in return what they like - otherwise it just gets awkward.

Georgia - So human politeness if anything else will just force you to engage?

Viren - Exactly.

Georgia - Now you also fed me a bad line, and the bad line you fed me was "I like reading" which I gave it a go.  So let's hear how I got on...

Georgia - I really like reading

Boy - Okay, so do I.

Georgia - Yes?

Boy - Yes.

Georgia - Great.

Boy - Yes.

Georgia - Okay.

Boy - Yes.  That was a bad chat up line.

Georgia - It wouldn't have worked?

Boy - No.

Georgia - What would you say would have been a good chat up line?

Boy - Maybe - I like reading Joseph Conrad.

Georgia - Oh - Heart of darkness, right?

Boy - Heart of darkness - that would work.

Georgia - Okay for next time.

Girl - You like Joseph Conrad?

Boy - Uh oh...

Georgia - Obviously that went really terribly.  There was no interaction at all and what I enjoyed is that his suggestion actually went down really badly with the girl I think he was seeing.  So what made this a bad chat up line?

Viren - Well it's a bad chat up line because it's a closed question.  You are essentially just stating a fact rather than trying to force reciprocity.  I guess for his partner - I guess it raises questions about how similar they really are.

Georgia - And I suppose something else to consider if you're trying chat up lines - don't go over to a couple...

Viren - And also, I think, maybe the important point to emphasise is that these chat up lines aren't going to work in every single situation.  If you went up to someone in a library and asked them what their pizza topping or favourite pizza topping is - it probably wouldn't work.

Georgia - There was one line that you fed me which I was actually too cowardly to try which was "you're short but that's alright because I like short people."  And this is something called "negging."  So tell me something about negging?

Viren - So negging is something proposed by lots of pickup artists and it's simply a man - usually a man - going up to a woman and using either a backhanded compliment or an offensive statement.  And the idea from pickup artistry is that this is supposed to make the woman more attracted to you.  The problem with negging is that I think firstly, the science doesn't support it - the science suggest that, actually, negging doesn't work - it's not a good way of approaching someone.  I think the bigger problem with pickup artistry is that it's simply based on misogyny.  It's based on this idea that you can deprogramme or dehumanise women and that's a good way to get them into bed with you.  Even if you did think that that was a good way of going about the world, the idea that you can lie and trick someone into having a relationship with you is not a good start for a future relationship.

Georgia - So - no negging then.  Well, do you have a top tip of final science hack for anyone who might be looking for love?

Viren - I get asked this question a lot and I always say that dating is stressful.  It is stressful for everyone because there is so much anxiety involved.  In fact, there are studies suggesting that at the start of a relationship, particularly in the first few months, your levels of cortisol start to increase suggesting that it is stressful, and because it's stressful we sometimes behave in silly ways.  And my advice really would be to just be kind to everyone, everyone is - everyone who's dating at least - is in the same boat and they're all being stressed, and they're all finding it difficult and, if you're kind, not just to other people but  also to yourself, I think it goes much better.

19:53 - Dating: past, present and future

How has dating changed through time, and is technology having an impact?

Dating: past, present and future
with Graihagh Jackson, The Naked Scientists & Viren Swami, Anglia Ruskin University

Now we've just heard how to attract people, but how do we actually go about early datingmeeting them? Chatup lines in a bar clearly aren't a great idea, and these days it seems people are using tech more and more. Graihagh Jackson has been looking into our dating pasts and presents....

Pat - This might interest you.  In the Isle of Man there was a hotel and they had tables all round the ballroom and on every table was a telephone, and if you fancied somebody at the other side of the room, you could ring her up.  And she would answer the phone and you'd say "would you care to have a dance with me."

Graihagh - That's not how my grandmother met my grandfather though...

Pat - How I met Eric, your grandfather, was on on the tennis courts and it just so happened that the girl I was with, she knew the two lads on the adjoining court.  So she introduced us and that's how our friendship began.

Graihagh - Did you manage to give him a good thrashing when you played him at tennis then?

Pat - No I didn't really - we were pretty evenly matched.

Graihagh - My grandmother had never really dated anyone before then.  Things were very different back then.  Today though is rather different - you don't necessarily have to approach someone in a bar or at a tea dance.  You can just ping them a message via one of the many dating websites or apps.

David - Well, it strikes me that the internet's perfect in that context...

Graihagh - Meet my dad David.  We were just saying how difficult it is to meet people when you're out and about.

David - If you were to take the view that you have to meet, let's say 200 people, in order to meet one person that was compatible, then internet dating provides that volume that you would otherwise struggle to find if you were relying on face to face encounters.  And, I guess in terms of the way you might approach it - I mean if you were thinking of it as a job interview, looking in terms of looking for a partner, you might in terms of analogy, try and encourage as many candidates as possible to apply and, in that sense, you kind of interview them.  So you can reduce it all to a bit of a process - I mean it's clearly a matter of the heart in the end.

Graihagh - This is slightly weird because you're discussing it with your daughter about your dating life.  But something that strikes me about the world of dating today is that things are much more casual, if you have to meet say 200 people.

David - Well at the risk of, as you say, discussing it with my daughter, in my mind it's a mistake to commit to something which has no sort of definable end.  So the whole evening, so dinner for example, would be a commitment a bit too far, in my view, on the first meeting because you still haven't really established any clear rapour.  So a coffee, in that casual sense, is a nice easy thing to do in my limited experience I hasten to add.

Graihagh - Dating is definitely more casual - I can vouch for that, but I think it goes further than that.  But this was something I definitely did not want to probe with my dad.  At least among my peers relationships start with sleeping with someone and then, maybe, it develops into something more. It's all about going with the flow and hanging out but, as a result, the definition of what the relationship is or isn't gets completely blurred and, in my experience, you have no idea what's going on.  So I rang up my brother Scotty to discuss my dating woes...

Scotty - Yes, there's quite a few different types of relationship in my mind.  So you can be seeing someone or you can be going out with them or you could just be, you know, friends with benefits - that sort of thing.

Graihagh - This new way of dating - supercasual with no clear boundaries and a choice of seemingly endless possible mates.  Is it a good or a bad thing?  Either way, the hapless romantic in me has always taken great comfort in what my dad told me last year...

David - That was when we were talking about when you were saying you were comfortable being single and that you had no real plans to meet anybody..

Graihagh - Mmm...

David - And that's when I said "you may not have any plans but if you meet somebody, you meet somebody no matter what you were thinking previously - love takes over."

Khakhil - That was Graihagh Jackson speaking to her Nanny Pat, her father, David and her brother Scott Jackson. Graihagh's with us now -

Which dating method sounded best to you?

Graihagh - It's really hard to tell I think because, ultimately, in the modern way of dating - how you and I might date.  Actually, there's a lot of confusion - are you dating someone are you not - ultimately that could lead to someone getting hurt.  But having said that, that can also work in your advantage if you're not sure where you want the relationship to go.  It's less defined, it's more flexible.  So I don't know really - I think it's each to their own and you take each situation as you go.

Khalil - Nowadays, especially with our generation, technology seems to be playing a bigger and bigger role.  It used to be online dating websites but now it's moving more into the app arena.  What kind of an impact do you think this is having on modern dating?

Graihagh - Yes, it's really interesting you say that cause, you know, my grandmother was telephone across a room.  My dad uses online dating websites whereas, I can't speak for Scotty - it's not something we talk about regularly.  But certainly for me, it's much more about the apps and less about your online profiles.  I think it's having a huge impact on how we date.  As I said before, things are becoming much, much more casual. I think it's just because you have a limitless number of people you can choose from and, as a result, you want to invest less time so that you can see more people but also there's this FOMO thing, this fear of missing out out - perhaps there's someone better just around the corner.

Khalil - Viren - I'm going to bring you back in here.  Is this something you've looked at?  Would you say apPs and technology are changing how we find love?

Viren - They're changing two things; they're changing where we meet our potential partners.  So about 30 years ago very few people would have met online and the majority of people would have met in what we would call closed spaces.  So closed space is any place  where you have to have an affiliation to join like university or work places and by far the majority of people would have met in these closed places.  The latest data suggests that increasingly people are meeting online or through dating apps.  The other thing that's changing is the nature of relationships.  It's changing the nature of relationships in the sense that people are self-presenting in a way that they haven't been able to before.  If you're meeting someone offline, you have to kind of have a negotiation of that relationship very quickly and trying to work out what that other person is like, and trying to find out what their personalities are like, what their hobbies etc., and so on are like.  Online you can get a lot of that information very quickly, even before you've met that person, and that short circuits the relationship process because you get that information.  The thing you need to do to work out once you meet that person is whether that information actually matches what they've said online.  The curious thing though is that most people, apparently, don't seem to lie very much on their online profiles.  They may lie - add a centimetre here or take a few pounds of there but people don't tend to lie very much because, obviously, the point of online dating is eventually meet someone and if you add 6 inches, you are going to get found out.

Khalil - I guess no-one wants to get caught out...

Graihagh - I find that very hard to believe.  I'm sure people have lied about their height or...

Viren - Im just telling you what the science says. I think there is a certain type of person who does lie on online dates all the time.

Graihagh - Mind you, I've had some horror story dates.  Maybe I'm just tarnished forever more...

27:47 - Your brain in love

What happens to the chemistry in your brain when you fall in love?

Your brain in love
with Connie Orbach, The Naked Scientists

Love is often considered the core force behind keeping couples together, but whatFMRI_image_of_lovers is it? Is it simply some chemicals in your brain, or and how can we go about studying it? Naked Scientist Connie Orbach joined Khalil Thirlaway to explain what science can tell us about love...

Connie - It can tell us an awful lot and not much at all, all at the same time, it would seem.  There seems to be three stages; so we've got the lust stage which I think you've already been talking about on the show.  It's the stage of attraction where you may be quite promiscuous, there's really high testosterone levels in males as well as females.

So after that we have the attraction stage and that's when the real high kicks in.  It's kind of the honeymoon period and you see really high levels of what's called monoamines at that point, which are chemicals in the brain.  You've got serotonin, dopamine also noradrenaline - these are all the kinds of things which give you a massive high and just make that period just absolutely amazing.

And finally, we have the attachment stage which is the bit which makes you want to stay together.

Khalil - So at this point in a relationship, what's going on in the brain and body chemistry?

Connie - Okay.  So there's a few different things going on and it's interesting that we say - love, it's all about chemistry because, actually, a lot of the time it is.  We've got huge changes in the chemical balances in our brain that happen around this time.  There's a few different really important hormones involved; we've got oxytocin which you may have heard of before - it's often called cuddling chemical.  It's the kind of thing that makes social bonding and social cohesion work; without it we're not very good in social situations.  We've also got vasopressin which is actually controlling heart rate and things like that, but we've seen it's really important in monogamous animals.  And when we've studied this, we've actually used an animal to study it  - the Prairie vole, and they're really cute little voles and what we find is that they actually nest together.  They stay together for life once they've got a partner and they bring up their children together, so they're kind of one of the best analogies that we have for humans.  What's also really useful with them is that there's a different type of vole, the Montane vole, which is really closely related but not monogamous.  So when we're looking at differences in the brains, we can compare the two and get a better idea of what's going on.

Now with these voles, if we knock out their ability to respond to the hormone I just mentioned, vasopressin, they actually can't form a monogamous bond - they don't stay together.  But, there's also something else which I find really interesting which is that dopamine gets involved here.  Now dopamine you might have heard of specifically with drug addiction and there's a reward pathway in the brain which is activated with dopamine. Now what we found in the Prairie voles is that before sex and after sex, dopamine can have a really different action.  Before sex, it's causing these Prairie voles to go out and be really promiscuous and find mates, and you know get out and meet people like we're always needing to do, or meet tiny little voles, I guess.  And after sex, it's actually causing them to be aggressive to other animals that are the same sex to them.  They essentially become jealous, possessive, Prairie voles.  The kind of thing that is the epitome of that horrible thing that happens in a relationship to your other half.

Khalil - I guess this one bit of the animal kingdom we don't quite want to emulate?

Connie - Yes, definitely!

Khalil - This idea of mating affecting your dopamine levels and almost making these voles addicted to their mate - kind of sounds like a drug?

Connie - Yes, it does.  And, I mean, I'm sure there's loads of songs talking about love as a drug.  It's hard to say that it's addictive because there's lots and lots of different things that set off the dopamine reward system and not all of them are addictive.  We have so many different myths thrown around like, chocolate's addictive.  And they may activate that pathway but there's a few other things that need to happen for something to be addictive, but it definitely gives you that high that addictive substances give you.

32:07 - Mythconception: Kissing is universal

Is kissing really seen as romantic the world over? It's less common than you might think...

Mythconception: Kissing is universal
with Kat Arney, The Naked Scientists

Think kissing comes naturally to all of us? Kat Arney has been investigating for a Rodin's The Kissromantically-charged mythconception...

Kat -  Love is in the air, and what better way to pass the time with a bit of kissing and canoodling with an attractive human of your choice? From pecking on the lips to a full-on snogging session, kissing is associated with romantic desire in popular culture the world over - in art, films, books, music videos and everything else, it's something done by lovers with intimate designs on each other. Or is it?

In fact,
a study published in 2015 by American anthropologists showed that around the world, just under half of the 168 cultures investigated liked to lock lips in a romantic setting - and many of those who didn't thought that the behaviour was actually pretty gross. In their paper, sexily titled "Is the Romantic-Sexual Kiss a Near Human Universal?", the researchers showed that only 46% of cultures fancied a snog. For example, out of 10 cultures studied in Europe, only seven kissed in a romantic way on the lips. Across the pond it's even fewer, with 18 out of 22 North American cultures playing tonsil hockey, and just four out of 33 in South America swapping their spit. By contrast, all ten of the Middle Eastern cultures in the study enjoyed a smooch, and in general, more socially complex cultures went in for kissing more than less complex ones, while hunter-gatherer societies tended to find it disgusting.

The research poured cold water on previous work suggesting that kissing was a near-universal display of love. This idea was supported by observations from scientists who had spotted chimps and bonobos having a cheeky snog, suggesting it might be something that goes way back in our evolutionary history. But the discovery that half of all cultures don't kiss shows that the belief that snogging is universal to humans is probably the result of an excessive focus on a small range of Western cultures as being representative of the entire world. The joy of ethnocentrism...

So, given that kissing must be a cultural phenomenon rather than an innate behaviour, why do any of us kiss at all? For a start, the cultures that do kiss believe that it's a good way to judge whether a potential partner is up for taking things further, and if they're likely to be sexually compatible - and, perhaps, to test more subtle cues about their health (and halitosis).
A questionnaire-based study found that kissing seems to be more important for bonding in long-term relationships than as a turn-on in the heat of passion - although many respondents said that a first kiss was a good way of checking out a potential partner's... errr... potential.

Building on this, a
2014 paper showed that test participants - particularly women - judged descriptions of people to be more attractive if they were told they were good kissers.

And on a more basic biological level, a
2014 study revealed that a ten second kiss results in around 80 million bacteria being swapped between snoggers, which might potentially help to boost immunity between partners.

Something to think about if you're lucky enough to have a willing partner to give you a big snog on Valentine's day. Although don't think too hard about all those bacteria - I wouldn't want to be responsible for putting you off!

35:10 - Could the pill affect your marriage?

When women come off birth control there can be a drop in marital satisfaction, according to research...

Could the pill affect your marriage?
with Dr Michelle Russell, North Carolina State University

Love is a chemical reaction in the brain, and is often described as a kind of drug.An assortment of drugs But can other drugs impact how you feel about someone? There has been recent research showing a surprising association: when women come off the contraceptive pill there can be a change in marital satisfaction. This might be due to disruptions of natural hormonal shifts that occur in fertile women. Georgia Mills spoke to researcher Michelle Russell, from North Carolina State University, to find out what might be causing this..

Michelle - We know from previous research that women experience shifts in the kind of  traits and characteristics that they tend to prefer in their partners, and that these shifts are associated with the shifts in the hormones that occur across the ovulatory cycle.  So, for example, women who are normally ovulating during their fertile period show stronger preferences for men who have symmetrical faces, who are more masculine.  The thing is though is that hormonal contraceptives can disrupt these hormonal shifts and I was really interested in what the implications were for the use of hormonal contraceptives for women who are in established relationships.  So we know that the majority of women in industrialised nations do use hormonal contraceptives at some point during their lives.  So a lot of women are starting relationships while they are using contraceptives, so they're not experiencing these natural shifts and preference that we would see with women who aren't using them and then, when they're in their relationships, many of them stop using them.  So basically what does it mean for these women to begin relationships not experiencing these normal shifts and then, during the relationship, start experiencing these shifts again.

Georgia - How did you go about looking into this relationship?

Michelle - We had two longitudinal studies of newlywed couples.  We had them go back and just give us their history of their contraceptive use from the time they started the relationship with their partner all the way up until the current point in that study. We get reports of their marital satisfaction every few months and then we also rated each of their partners - we rated their attractiveness.  So we actually trained a team of coders to go through and rate the attractiveness for all of the husbands, and the wives as well in this sample.

Georgia - Sorry - you trained people to rate how attractive someone is...

Michelle - I know.  It sounds really really funny.  And you know people think - oh how objective can you be when it comes to rating attractiveness but, in general, we see -  and this is across cultures - that people are remarkably insistent when it comes to deciding what's attractive and what's not: bone structure, facial symmetries, skin clarity, so we had them looking for specific characteristics.  But I will say, it doesn't take very long to get people reliable when it comes to rating attractiveness.  We all had pretty consistent ratings, pretty quickly.

Georgia - Taking this data of the women on and off contraceptive pills alongside the husband's attractiveness.  What did you actually find out?

Michelle - So what we found was that among women who began their relationships while using hormonal contraceptives - they get into this relationship and once they stop using hormonal contraceptives, women who were married to men who were relatively more attractive actually had higher relationship satisfactions.  So they were happier with their relationship once they stopped using hormonal contraceptives if their husband was also relatively more attractive.  For the wives who were unfortunately married to the relatively less attractive husbands, we saw a decrease in their relationship satisfaction.  So they were actually less happy with their relationships once they stopped using hormonal contraceptives.

Georgia - Why should there be this difference?

Michelle - Well, what we think is going on is that, again like I said, so women are experiencing natural shifts in preferences across their ovulatory cycle, and what we think what may be going on is that when women are using hormonal contraceptives - so we've already seen from previous research that women actually choose different partners when they're using hormonal contraceptives than do women who aren't using them.  So they tend to choose partners who are slightly less masculine, slightly less attractive.  And we think what might be going on is that while they're using hormonal contraceptives, they might prioritise attractiveness a little bit less than women who aren't using them.  And then what happens is that when they stop taking hormonal contraceptives, they start experiencing these shifts again, so this might become something that becomes a little bit more important to them at this point.  So for those women who are married to a man who is relatively more attractive - well you know it works out then that their prioritising this a little bit more because their partner has that characteristic.  Whereas for those women who have the relatively less attractive partners, suddenly this partners not necessarily meeting all of those priorities that they might be experiencing now.

Georgia - And what you've discovered is a relationship.  So we haven't been able to set aside these things and say this is causing that.  But the relationship is very interesting and I'm surprised to think that something as small as a little pill can actually change how happy you are with your marriage...

Michelle - It is.  And so yes, as you said, it's not experimental so we absolutely have to be careful when we make any sort of causal explanations for this, and it is something... It's important to point out too that, you know, I've been studying relationships for many, many years now and the thing that you learn when you're studying relationships and what influences relationship satisfaction, is that there's so many different factors.  And that yes, this does have an effect on relationship satisfaction but it's not a huge effect - it's about the same effect size as we would see for other factors that predict relationship satisfaction.  And so, it's a small part of the puzzle but it's interesting because again, the prevalence of hormonal contraceptives, for women to use them as much as they do we really don't know... You know we know more about physiologically what they do to women but not necessarily what it means for their relationships and it's, you know, as a woman I would want to know.  I'd would want to make sure that I'm informed when I'm taking medication and everything so I think this is just one small piece of information that women might want to have, to consider.  Again, I don't think it's nearly enough to tell women to stop taking them or anything - that's absolutely not something we would ever, ever recommend.  But again, a small piece to the puzzle that women might want to consider.

41:52 - Undercover statistics

Do men really have more partners than women, and why are we having less sex than ever?

Undercover statistics
with Professor David Spiegelhalter, University of Cambridge

Sex and statistics may sound like unlikely bedfellows, but stats are one of the onlyPeeping Tom ways we can actually get an idea of what's going on behind closed doors and under the covers, and we can peek at how human behaviour is changing over time. So what do the numbers say, and can we really trust them? Professor David Spieglehalter is a statistican at Cambridge University, and he explained some of the surprising things we can learn from crunching the numbers to Khalil Thirlaway...

David - Statistics are the way we can actually find out what really is going on or, at least, as best we can.  So we don't just have to listen to people's stories, their anecdotes, their boasts maybe, we can actually try to do the numbers.  Now sometimes we can work out the numbers from official statistics, really good statistics - you know, we know how many babies are born.  It used to be an interesting statistic to correlate birth records with marriage records and find out, for example, what proportion of women were pregnant when they got married - it was usually about 30%, so sometimes we can get some very good numbers like that. Other times we really just have to ask people about their behaviour, what they get up to, but then there are good and bad ways of doing that.

Khalil - How reliable are these various methods of asking people about their experiences?

David - Well, there are some terrible methods. If you just put up a survey, an online survey or a little insert in a magazine, as there used to be and asked people to fill this in and send it in if they felt like it, you're going to learn nothing.  Even if you get a big response rate - you know thousands - ten thousand people might respond, it still only says something about those ten thousand people, which is okay, but you don't really learn anything about what's going on in the general population.  If you really want to have an idea about what's going on in the whole country, you have to try to get a representative sample to respond.  You can do random sampling techniques, you know using standard survey methods, the problem then is getting people to actually answer the questions and getting them to give reliable answers.  And there's all sorts of methods that people have gone about to try to do that.  The big UK survey is known as Natsal - it costs about £7 million each time.  They do it every ten years and that relies on face to face interviewers going into people's houses, gaining their trust - they get about £30 a moderate fee for taking part - but they build a little relationship, not a very personal relationship but, by assuring the person that this information is valuable, it's good for planning health services, it's a contribution to society, they get around a 66% response rate, which doesn't sound great but it's much better than most surveys.  And the other crucial thing is that when the questions are asked now, the interviewer doesn't hear the responses - it's all done on a computer.  So the person being interviewed enters their answers to the questions in and then the computer's locked down and the interviewer never know what's actually said.  So when you're asking what could be slightly embarrassing  questions or difficult questions about age of first sex, how many partners you've had, have you had concurrent relationships, as it's known, when you've got two or more sexual partners going on at the same time - people will answer those sorts of questions.

Khalil - Surely the responses to these surveys do depend on honesty on the parts of the participants?

David - Yes, and there's various checks built in within the interview to check the person isn't contradicting themselves from previous answers.  There's also checks amongst the whole survey to correlate with previous surveys.  Interestingly, if you asked 30 year olds in the year 2000 when they first had sex and you ask a random group of 40 year olds in the year 2010 when they first had sex, you should get roughly the same answer.  But there's one check the data absolutely always fails.  It's a mathematical fact that if you've got an equal number of men and women of the same age distribution and you ask them how many sexual partners have you had in your lifetime, then the average, that's the mean average (the total number of partners divided by the number of people), should be the same for both men and women because each partnership requires a man and a woman.  We're talking about opposite sex partnerships here.  But it always in surveys men claim to have had a larger number of sexual partners on average than women do.  Now, as we said, this is a mathematical impossibility but the gap is lower than it used to be.  It always used to be that men said they had twice as many as women did which is so wonderfully impossible, and the gap's gone down, but it's still there for the whole lifetime.  And this is a bit of problem, of course, for sexual searches and a lot of effort has gone into trying to identify why this might be the case.  It could be just be because men boast and women are very reticent and there's a suggestion that men tend to round up and women tend to round down.

Now there is some evidence that psychologists have got of what's called "social desirability bias," just the fact that women might be slight less willing to acknowledge multiple sexual partners, and there's this wonderful experiment that some American psychologists did where the randomly allocated students to three different ways of responding to a sex survey.  And one of them was very confidential, one of them had the threat of exposure that they knew that one of their friends, one of their other students would pick up the form and take it away and, in the third arm, they were actually wired up to a lie detector actually it wasn't a lie detector, it was a fake lie detector - the little pen going wiggly, wiggly and all this stuff, but they thought they were.  And they showed that for women, not so much for men, that if the people wired up to the lie detector acknowledged having a greater number of sexual partners and actually then matching the number that the men had said.  So not a big effect, but enough to suggest that that is also part of the reason.

Khalil - What do these data tell us about how our sex lives have changed over the years?

David - Yes, I think this is one of the most interesting things.  Now, for example, the big British survey's been done three times, so 1990, roughly 2000, 2010 you can start looking at the trends and even if there's some uncertainty about the numbers the trends, you think, are fairly reliable.  And there are some, you know I suppose, slightly surprising trends for example, the frequency of sex has gone down over the last twenty years - that's the one people often pick on as being interesting.   And that's even among couples who are together, couples 16-44 year old, opposite sex couples, on average in 1990 had sex five times every four weeks, then it went down to four and now it's three and so all sorts of reasons.  Of course, I'm a statistician, it's not my job to say why this happens but the people, the actual researchers who did the survey have, under considerable media pressure, come up with their sort of ideas of the theory of why this might happen in that they think that quite a lot of the responsibility is just, people's lives have changed so much.  Our interconnectivity, our smartphones or our ipads or whatever are there all the time right through the evening - even into bed maybe and so, this constant connection with the outside world, you know, they think that might have reduced that time of just personal intimacy.

Khalil - Not now darling - I'm playing angry birds...

David - Or I'm watching the latest box set or something or other.

49:21 - Did we evolve big brains to be sexy?

Are human big brains the equivalent of the peacock's tail?

Did we evolve big brains to be sexy?
with Professor Geoffrey Miller, University of New Mexico

If you look at the world around us, it's brimming with art, music and technology. ButChess painting, humour and music don't contribute to survival, so why did they evolve? In his book The Mating Mind, Professor Geoffrey Miller argues that a process called sexual selection, which causes "sexy" traits to remain in the gene pool, could be at the heart of many of humanity's unique features, as he explained to Georgia Mills...

Geoffrey - Bare in mind, every single one of your ancestors all the way back millions of years, succeeded not just in surviving and making a living but also attracting a mate, keeping them around long enough to raise kids together and, basically, being sexually and romantically successful.  All of our would-be ancestors who failed to attract a mate, no matter how good they were at surviving, did not pass on their genes and did not become our ancestors.

Georgia - This drive to reproduce means we have traits that make us sexy but that don't necessarily help us to survive.  Think about the Peacock's tail - it's probably not going to help them avoid being eaten - probably the opposite.  But the big feathers and bright colours show off the male's genetic quality, so females rather like them, and us humans have our own versions of the peacock's tail...

Geoffrey - I think in humans, we have physical equivalents.  Things like male beards, male upper body muscles, female breasts and buttocks.  Any traits that are elaborated beyond the requirements of surviving and parenting.  But beyond that, we have mentally attractive traits that are also romantically compelling - things like intelligence, creativity, sense of humour, artistic and musical abilities, and even moral virtues.

Georgia - You kind of just listed almost everything about people there in one go.  Why would someone find these traits attractive?

Geoffrey - I think these traits are all attractive because they testify that your brain works pretty well.  It's hard to produce these if you've got brain damage, or if you're the result of siblings, or cousins getting married and having genetic inbreeding problems, so it's a pretty good testament to your brain quality and, in turn, you genetic quality.  So I think that's why we pay a lot of attention to these, we're doing a sort of unconscious quality assessment. 

It's something Freud talked about a century ago.  And I'm by no means a fan of Freud but I think he was on to something that, if we were only motivated to survive to take care of our kids, an awful lot of human civilisational achievements would not have happened.  An awful lot of art and music and intellectual progress would not have happened if we hadn't had this drive to attract mates. No doubt, intelligence itself is useful in every possible domain of life.  But things like sense of humour are so bizarre because you can't scare away a sabre tooth cat by making a joke at it.  It doesn't really help you find nuts and berries in the wild, but it's very useful socially and it's particularly useful in sexual and romantic contexts.

Georgia - You mentioned music and I know when I think about guitar playing, people in bands - they're quite attractive.  And you argue that this is sort of a sign that your brain works well, there's positive things going on behind the scenes.  But then if you think of someone who's maybe a chess player doing really well, I can't see the same 'fandom' breaking out about it.  What's the difference there?

Geoffrey - Yes, there's a crucial difference between music and chess in that our ancestors were making music to attract each other for at least 30,000 years.  We have good evidence from bone flutes from Germany.   So we know music is ancient, and that means we could evolve, made preferences to be attracted to music.  Chess, on the other hand, is only about 1,000 years old so we haven't really had the instincts to find grand masters romantically compelling but, if we wait another 10,000 years, it might be that chess becomes as romantically compelling as music is now.  It's hard to predict those things but it's quite possible.

Georgia - You also mentioned kindness, morality, and I know that's something that has sort of natural selection a bit stumped because the whole idea is, you go after something that improves your own survival.  So how would sexual selection explain morality?

Geoffrey - If you're somebody, particularly as a potential long term partner, you really want to be able to trust them, communicate effectively with them, be confident that they have your best interests at heart.  So our ancestors would have favoured mates who have the moral virtues that predict being a good partner and a good parent and that, I think, is important on Valentine's day when you're basically doing signs of romantic commitment to say look, here are my moral virtues as they relate to my love for you.  Here's how I express them.  And then if that succeeds somebody goes 'ahh, they're a good person, good boy, good girl, I want them, I can trust them.'

Georgia - I mean the message there is kind of half sweet and half a bit depressing like they're being kind to you but it's just to keep you on side - it's all part of the long game...

Geoffrey - Yes.  I mean that's the funny thing about virtue signalling is that you're kind of showing off your innermost qualities in a somewhat ostentatious way.  And when it comes to people giving lots of money to ineffective charities, that's a bad form of virtue signalling because they're just burning money and saying, look look at me, I'm so generous.  But when it comes to romantic things like writing, you know, erotic poetry or skyping with your beloved when they are away at a conference, that's good stuff.  That actually does deliver real value to the other person and it testifies to your moral virtues so, I think, that stuff is great.

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