by Sara Pascoe
If two birds collaborate to warm and feed, the chicks will hatch and then they’ll need more than one pair of wings at their beak and call. The demands of rearing chicks create pair bonds between adult birds who reproduce. Birds are monogamous because their young require the input of two parents. This isn’t romance, it’s evolutionary necessity.
We should also clarify what biologists mean when they call a species ‘monogamous’. It might not be what you mean by monogamy, and a bird could really break your heart. For biologists, ‘monogamous’ means that a pair share a nest/home, raise their young together and have selective (not exclusive) mating.
Should I emphasise the ‘not exclusive’?
Being powerfully pair bonded, shared care of a brood – these things don’t necessitate fidelity. Some amount of copulation outside of the pair bond may be of benefit to both sexes. THIS IS NOT ‘CHEATING’, it increases the chance of reproductive success – it is winning. No human lover will accept this excuse, by the way, and I. Have. Tried.
Only around 5 per cent of mammals are monogamous, it’s much rarer than in birds. That’s because, as you may have noticed, we don’t lay eggs. We lay our young without shells. They gestate internally and are fed by lactation during early life. Most female mammals can do all this by themselves, they don’t need no man, and yet you don’t see them wiggling round and bragging about it like Destiny’s Child. The only mammals who form pair bonds are those who need two parents for survival. And that’s the story of how humans grew big brains and got dads.
* Being more compact means the body can stay warm using fewer calories. It’s why people who have evolved in harsher climates like the Arctic are shorter and squatter, while people on the equator are lither and leggier.
† Fun fact: my editor Laura is heavily pregnant and having to read and reread horrible sentences like this, and I won’t lie, that’s spurring me on.
‡ Not you, Laura.
§ Not you, audio book.
¶ Feel free to cut and paste this into any ‘Congratulations, you’re pregnant!’ cards.
|| It is worth noting that loving people often has an aggressive opposite. The more we love, the more we seek to protect, defend. Love has potential violence built in.
Chemical Romance
It’s believed humans’ ancestors lived in groups co-operating socially for around thirty-five million years before they coupled up to care for their increasingly dependent babies. Millions of years of freedom, ruined. Obviously, the adaptation to dual parenting was very gradual, not one awful morning when men suddenly found themselves accountable for sexual consequences.* And before you blame this on nagging bitches, no one was telling men to babysit and wipe bums. Children who received the resources and protection of a male were more likely to survive and the genes of fatherly men were replicated in greater numbers. Over hundreds of generations males became more nurturing and increasingly bonded in two directions – towards their offspring and towards their partner. Over thousands of generations what we refer to as ‘the nuclear family’ was created within our social tribes.
So how does a behaviour trait evolve? In this case, genes responsible for the chemicals that bond people were selected for. As weird as it is to think about, what we call love isn’t a magic, unknowable force but a very scientific assortment of neurotransmitters and hormones. That’s all emotions are. What you feel is often controlled by tiny amounts of amino acids. The most important chemical associated with all kinds of human attachment is oxytocin.
A bit of background: oxytocin was discovered in 1906 by Henry Dale, a pharmacologist, Nobel prize-winner and Gemini. Oxytocin can be a manual labourer, responsible for muscly jobs like the lactation process and contracting the womb for menstruation and childbirth. The hormone also has non-physical roles, emotional admin stuff. It makes you feel relaxed, soothed, connected.
Studies suggest that oxytocin initially motivated group living and was later hijacked for one-on-one bonding. It’s so fascinating to think of a hormone working that way, initially creating bonds between family members and local friends, then over thousands of generations becoming the reason we fall in love with the people we sleep with. Sorry, I mean sometimes fall in love with the people we sleep with.
Oxytocin influences what we consider to be our ‘rational’, ‘conscious’ behaviour. A study conducted in 2007 found that people who sniffed an oxytocin spray were 80 per cent more generous in sharing money with a stranger than people who’d sniffed a placebo spray – you know what perfume to wear before meeting your bank manager. Make sure you give them a nice tight hug as well. Bodily contact will get their oxytocin flowing before you’re thrown out of the building. Many studies have shown the link between oxytocin and empathy; in 2009 neuroeconomists Jorge Barraza and Paul Zak showed how watching an emotional video raised the oxytocin in people’s blood by 47 per cent, and intranasal sprays have been shown to increase people’s ability to read facial expressions – literally enabling better understanding of others. All this is so integral to how we live as a social species. When we feel ‘connected’ and ‘in tribe’ we are kinder, more respectful, more thoughtful. If you’ve ever sung with a group or played team games you’ll have felt the surges of in-ness. Playing with a team requires co-operation, perceptiveness – oxytocin. Scientists have proved that the more bonded a team feel to each other, the better they play.
Oxytocin is also why your mum likes you, playing a vital part in mother–infant attachment. Maternal bonding is thought to have developed first and subsequently those neural and molecular mechanisms were co-opted into partner bonds. ISN’T THAT CRAZY? Mum and baby became dating and romance. This means my boyfriend is like a son I have sex with!
I’m going to be sick.
He didn’t like that analogy either.
While we’re on the topic, sex increases the level of oxytocin in our bodies, with a huge spike when we orgasm. This creates a feeling of intimacy and closeness. I get overwhelmed with it sometimes, I feel so much love in my body it completely changes my mood, how I feel about the world.
More generous with your money?
Do not try to wank the bank manager.
Oxytocin also acts as a tranquilliser, making us sleepy and relaxed, because it counteracts the stress hormone cortisol. But the hormonal cocktail released while orgasming is different in male and female bodies. Males have a higher level of testosterone, which is thought to cancel out some of the intimate effect of oxytocin.
That’s why chicks wanna cuddle after sex but men don’t?
That is a cliché and an unhealthy case of gender stereotyping but also, yeah. It’s something to bear in mind if your post-orgasmic mood is unlike your partner’s. It can be very different from body to body, from day to day, and influenced by many things.
It’s interesting to consider how powerfully chemicals can affect us. Emotions we attribute to our personality or a response to events are actually chemical compounds bobbing around in our bloodstream. Let’s explore another one.
* ‘Sexual consequences’ is the best way to refer to your friends’ children.
V Is for Vole
And vasopressin, which seems to produce the long-term attachment needed for raising children. At least it does in prairie voles.
I don’t like animal experiments – partly for ethical reasons, but also because the findings are not directly applicable to us. But it’s difficult to do lots of tests on people because of political correctness gone mad human rights. Every time I thought I’d found an interesting study about the effects of vasopressin on the human male, the third page would reveal this male lived on a prairie and enjoyed a diet of bulbs and tubers.
Some hot facts for you: vasopressin is made in the brain by the hypothalamus and along with your kidneys works as an antidiuretic to regulate the amount of water in your blood. The hormone is present in both sexes, but males produce more than females – at least in voles.
Voles have earned this focus because there are two kinds, genetica
lly almost identical, but with very different mating strategies. Prairie voles are super devoted to each other and mate for life, cuddling and nestling and raising their pups together. If their partner dies, over 80 per cent never celebrate by marrying someone younger create a new pair bond. Montane voles, who look and behave the same in every other way, are not monogamous. The females raise offspring by themselves and the pups feed themselves by two weeks of age. Dad’s nowhere to be seen.
It appears the voles’ mating strategies have evolved in response to their environments. The prairie vole encounters a much harsher habitat with a meagre food supply, which results in a low vole population density. There aren’t many mates around and so these voles can’t be fussy. If a male vole were to remain free, single and playing the prairie, he would risk never finding a fertile female. Natural selection has favoured the males who ‘settle down’ with the right vole first female they find.
In biological terms, this is a trade-off. The prairie voles have evolved in a difficult environment to have ‘high-quality, low-quantity offspring’. The vole parents have fewer pups and do more for them to increase their chances of surviving the godawful prairie. The montane voles, who enjoy a lusher landscape and plentiful food supply, can afford to be laissez-faire. They practise a ‘low-quality, high-quantity’ strategy, popping out pups and letting them fend for themselves because the environment is easier to survive in.
What is so interesting about human beings is that we deploy both strategies, sometimes dependent on economics or resources and sometimes in complete disregard of those factors. Our species demonstrates a flexibility, a sign of how well equipped we are for responding to environmental signals. If we were voles, all rich people would be swingers with hundreds of children and all struggling families would have deeply devoted parents and only one or two kids. Both my parents came from poor backgrounds, yet my dad is one of nine and my mum one of seven. Sometimes having many children can be a response to high infant mortality: having more children can increase the chance of some surviving even if resources are reduced. Also humans respond to our culture as well as the environment. Some religions encourage having many children, and both of my grandmothers were rabbits Catholic.
Another component to coupling up that’s found in humans and voles alike – in all animals actually – is mate value. Taken straight from Darwin’s theories, every potential mate can be assessed by what they are offering. Many factors may be taken into subconscious consideration, but mainly age, health and behaviour. Voles’ compatibility will be decided by pheromones and fertility, with the prairie vole’s only selective criterion being ‘Were you there first?’ This demonstrates what is called ‘relative mate value’. The more partners an animal has to choose from, the more selective they’re able to be. They can reject the sick and injured; they can opt for the fellow with the prettiest hair or the better nest.
In the majority of animals it’s females who choose, while males must compete to impress them. Male peacocks have evolved beautiful plumage, bower birds build intricate nests, gorillas display size, strength and dominance. In fewer species, and only where the male has been lumbered with the larger parental investment, the females must compete to impress males. Seahorses are a good example, and poison arrow frogs. The dating game is always predicated on who gets stuck with the offspring.
And we know that this is not so simple with humans. With two parents each potentially investing a great deal of time, effort and resources into any young, both males and females must work to impress others with their mate value. However, it’s worth remembering that what heterosexual humans are trying to demonstrate to each other is not the same. Women are not preoccupied with appearing strong and able to protect and provide. Men are not overly concerned with looking younger than they are while maintaining a small waist and curvy bottom. Judging mate value in humans is beautifully complex, and, as we’ll be exploring later, very different for the sexes.
Research undertaken on voles has indicated the importance of oxytocin and vasopressin in creating their monogamy. In some outrageously cruel/informative experiments scientists gave male prairie voles a vasopressin blocker before they mated, which prevented them developing a partner preference. They then did the opposite – infused the males with vasopressin during a brief introduction to a female – and found they bonded even without sex. With female prairie voles, they found that administering oxytocin-blocking drugs stopped them developing a partner preference. It’s a lab-based Midsummer Night’s Dream, the scientists injecting potions and the voles waking up in or out of love … except all the characters are in cages and have their brains cut open at the end.
But guess what? In 2001, further studies found that some populations of prairie voles are NOT MONOGAMOUS, gasp. It seems they can be pretty flexible; if food becomes more plentiful and populations rise, mate value decreases and they don’t need each other any more. Mr Vole can pack his stuff and get the hell out. This proves that nothing is ever as simple as genes or hormones and their receptors – these things are always working in concert with environmental factors. Animal species that rigidly refuse to respond to environmental changes die out – I’m looking at you, pandas.
Fish just need to learn to breathe plastic bottles and straws.
Exactly. With humans, the reason we are the most successful species of all time is because we are so responsive and adaptive. We’re variable, flexible and sexy. It’s worth repeating that nothing discovered about voles can be directly applied to humans, of course. We must look to human experiments for that. There’s one that tested the blood levels of oxytocin and vasopressin in human men as they masturbated, and found that these hormones rose several-fold as orgasm approached. This supports the theory that human pair bonding has a chemical basis. And if the feelings of affection and closeness that facilitate monogamy are increased with sexual contact, this would at least partly explain why we have SO MUCH SEX.
Another unique trait in the sex lives of humans is the seeming pointlessness of much of it. The vast majority of creatures only mate when reproduction is possible. This is usually dictated by the female: her body signals that she’s fertile, either through pheromones or physical changes; this arouses the male; they do it; baby animals are made. With our beloved prairie voles the female has her ovulation induced by the smell of male urine. It’s a sure sign there’s a male nearby and so her body gets ready for mating. The exact opposite of a human female getting a whiff of urinals in a nightclub and her vagina falling off in disgust.
An important thing for us to consider is that unlike most mammals, human females have evolved ‘concealed ovulation’. Our bodies do not signal whether or not we are fertile in any reliable way. Males have no way of ascertaining if a female they copulate with will conceive or not. This has HUGE ramifications in our sexual behaviour, which we’ll investigate further in the chapter ‘Constant Sexual Signalling’. First, we must meet another of the chemicals underlying our sexuality, dopamine.
Addicted to Love
In order to get stuff, an animal has to want it. Animals need quite a lot of things to stay alive, so wanting stuff is pretty integral. Much of this wanting is created by dopamine, a neurotransmitter in the brain which sends signals between brain cells. These chemical communications are referred to as ‘dopamine pathways’ and are relevant to ‘reward-motivated behaviour’, which is a complicated way of saying, ‘When we want things, we do things.’
Dopamine is released in amounts which affect how much we want something and how motivated we’ll feel to get it. If we think of ‘rewards’ as the resources an animal needs to be evolutionarily successful, like food or sex, then the animal’s desire should correspond to how beneficial the reward would be. People talk about ‘dangling a carrot’ as an incentive, which is stupid because no one wants a bloody carrot. I’ve got friends who give their children vegetables as treats and I judge those friends terribly. Humans need energy to fuel themselves and carrots only have a little bit of energy. We might eat t
hem if they’re right there on the plate but we’re not going to run down to the shops especially. Doughnuts, though, doughnuts contain thousands of calories and lots of lovely fat and so we really want them. Think how long the energy in a doughnut would power you and it’s obvious why they’re far more appetising than carrots. If you’re craving one now, that’s dopamine, and if someone gave some to your kids, that was me.
It’s important to clarify that dopamine is not released when a goal is achieved, but beforehand. The brain assesses how something might help our survival and gives us a little hit of dopamine in expectation. It’s the anticipation of a goal being reached that stimulates the release of dopamine, hence the motivation. Dopamine acts as a subconscious incentive to human actions and behaviour because it makes us feel very nice indeed. It’s referred to as the ‘feel-good hormone’ in pop science books and is available in large quantities via drugs like cocaine from the kids your mum won’t let you play with. Dopamine can create bliss and euphoria at its best and a deep contentedness when being pro-social or altruistic. It also has a major function in romance.
When it comes to human pair bonding or ‘falling in love’, the deep longing and lust is created by reward circuitry in the brain called the mesolimbic pathway. Dopamine is made by the hypothalamus and then passes to the ventral tegmental area of the midbrain and the ventral striatum of basal ganglia in the forebrain. This is how the brain inspires reward-seeking behaviours: the more dopamine that is released into the circuit, the more motivated an animal is to achieve a reward.
