This is for you. I love you.
Love is the quintessential romantic, irrational, human experience. It is in the first place the domain of its clients,
although readily owned by the poets. As for others. The philosophers
are permitted access, thought they often regress into poets too; describing love as sacred, profound,
and utterly existential. In the penultimate place in the line for
love, in front only of the lawyers whose focus is appallingly
materialistic, are the scientists. But the scientists too are accused
of materialism, of soulless reductionism, mistaking passion for a
am here as a scientist, though you would do well to remember that
behind the label stands another human being, and the scars I bear you
may recognize too. I am here to answer that trite question, “What
can science ever know of love?” That question is too broad for my
mind, and I write with a more particular view in mind. Thus, ladies
and gentlemen, lovers and scorned alike, I present to you, a great
and amazing production, written using the quills of Cupid's arrows,
and inspired by the musings of the great bard himself. I give you:
Molecular Neurobiology of Pair Bonding
scene is familiar. You were there. And so was I. Cocooned in
sunlight. Starry heavens. Watching. Holding. Kissing. Wanting.
Having. Do you remember the shape of the moon as I held you by the
side of the silent road. I remember the rhythm of your breath. You
were asleep when I told you this is perfect. I write this now, tired,
sick, alone, remembering. And you?
put, love is the phenomenological correlate of a behavioural tendency
which favours pair bonding, and that is an evolutionary selected
strategy benefiting offspring survival in particular species. In
other words, love induces an obsession with a potential mate,
eliciting a preference for monogamy, and this effect naturally
overlaps with a period of time sufficient for the conception and
protection of maturing progeny.
might as well note here that, scientifically speaking, it is unclear
whether humans are biologically monogamous (cf. culturally), nor what
is the length of time of human monogamy (cf. culturally).
step right up, five pence to the bearded woman if you don't mind, and
I promise entertainment, education, and if you're good, a baring of
my very heart and soul.
shall explain the following. Most prominently, I describe the
molecular components known to be involved in pair bonding (you say
love I say potata). There shall be talk of the avenues of the brain
in which these molecules are to be found. And all is topped by a
conclusion in the form of a philosophical coda, a musing on the music
of the cells.
seems likely that the pair bonding instinct evolved from other
behaviours, like the care of a mother for her offspring. Not only are
the two behaviours similar, as well as both being called “love”,
they also share molecular mechanisms. Oxytocin. It's a molecule.
Important for forming a bond between a child and their mother,
enhanced by behaviours like grooming and breast feeding, it is also
important for birthing, when a giant surge can precipitate labour.
is famous as the “trust molecule”, as dosing enhances our
tendency to trust those around us. A less well known fact is that it
can enhance our mistrust of strangers; yin-yang. Thus it can be seen
boyfriend/girlfriend love is a capacity that evolved out of the more
primordial maternal love, which itself is a subset of an even more
general tendency to stick together with those you know and away from
those you don't.
oxytocin operates its less famous cousin, vasopressin, which in
itself is better known for regulating fluids (sexy!) It
synergizes oxytocin's effects and its presence is at least necessary
for strong pair-bonding.
make me happy
Obviously not just anywhere in the brain. But basically, the reason
you're stupidly happily in love is because of some errant dopamine
flinging itself about in a rather unbecoming manner. Dopamine is the
neurotransmitter the media loves to talk about. It makes for a good,
simple story - “the reward molecule”, a fact only in part.
dopamine is involved in such horrors as addiction and experiences of
euphoria. It's also linked to the formation
of relationships, as well as forni-fucking (for want of a
word). So far, it makes perfect, simple, sense; love is predicated on
a reward-mechanism. But that's too simplistic, and as I hope you'll
find clear before long, dopamine is involved also in inhibiting
pair-bonding, and molecules in the body don't have jobs like
“happiness”, and “love”.
then what are these molecules doing?
if there's no love molecule, what's the significance of all these
molecules? Without getting into the nitty gritty of brains and neurons and neurotransmitters and receptors and action potentials and long term potentiation and Bayesian statistics, I can say the
brain is a jumble of tendencies. These tendencies can cause you to
commit a behaviour, but they can also be affected by what you do or
experience. For instance, if you were to engage in nurturing
behaviour then parts of your brain will respond by sending oxytocin
into the parts of your brain that trust your friends and encourage
that tendency. That happens by making that part of the brain more
receptive to future oxytocin, as well as more likely to send signals
to other parts of the brain.
gets tricky when we start thinking about the molecules which are
actually affected. Oxytocin and dopamine can react with different
receptor molecules, which leads to some counter intuitive effects.
For instance, although the “D2” dopamine receptor is vital for
post-coital pair-bonding, the D1 dopamine receptor inhibits
pair-bonding. This is the case because the particulars of D1's
location is such so as to prevent one from falling in love with
everyone you meet after sex (well, only the nice people are an
of words but what's happening
is an incomplete story, but it's a nice one, and will hopefully give
some impression of some of what happens.
one, Alex and Alice flirt and maybe a back rub is involved, but most
certainly they mix their private parts. They later spend a lot of
time together, and fall in love.
what happened to poor Alice. The flirting and grooming behaviours
engaged her oxytocin pumps, sending them into two important systems:
one is involved in the sense of reward (nucleus accumbens, part of
the mesolimbic pathway), and the other is more generally social
(ventral pallidum, where it meets vasopressin). Thus Alice already
feels trust for Alex. But it gets worse. The pre-existing oxytocin
combines with dopamine and even more oxytocin during and after sex.
This has a couple of effects. One is a longer term bias towards
monogamy with Alex, and away from others. The other establishes even
greater potential for affection for Alex. The dopamine plus oxytocin
combo enhances the ongoing production of oxytocin's receptor (in the
nucleus accumbens, this is achieved via histone deacteylation so as
to enhance transcription of the receptor's gene, and consequent,
parallel translation). The effect of higher amounts of receptors
means that Alice is more vulnerable to the effects of future
oxytocin, so that Alex's advances are all but certain to succeed.
This is all, of course, a viscous cycle, engaging a positive feedback
loop that is enhanced by sex and happiness. Ugh.
cool, I think I get it
Well, I don't, but never mind. Let's change track and focus on how
complicated it can get. After acknowledging that the above was an
incomplete picture, let's zoom into one detail. The oxytocin's
receptor's gene is called OXTR.
OXTR gene can have various “point mutations”, this is when some
of the atoms in the gene are different from the average. Genes are
made up of molecules that can easily be thought of as letters. The
OXTR gene has over 19,000 letters. Most point mutations have not been
studied, and of those that have been recorded, most have no effect,
and of course, some have a lethal effect. In between those extremes
are single letter changes that are associated with a range of
behavioural abnormalities. These include not only autistic
tendencies, but also differences to threat-associated-prosocial
behaviours, sensitivity of parenting (including capacity for hearing
infants' cries), the stress-protective-effects-of-socializing, and
of these changes must be due to developmental effects, that is,
relating to the role of oxytocin in the formation of the brain, a
topic well outside the current perusal. But some of these changes are
due to a more interesting subtle effect. Perhaps a slight change in
the way oxytocin interacts with the receptor, or in the way the
receptor interacts with other receptors, or in the locations in the
cell that the receptor preferentially positions itself, or in its
capacity to dock associated molecules in the cell, or in its tendency
to be made (i.e. transcribed or translated) or trafficked (e.g.
through the endoplasmic reticulum and Golgi), or in its effects on
DNA topology, or in any of a huge number of other possibilities, or,
almost certainly, in some combination thereof. Love is all so very complicated.
love is just a chemical reaction and we're all robots doomed to our
I see it like this. Without questioning whether our lives are predestined and whether we have free-will (pro-tip: yes and yes), we can ask what it means to value a particular set of experiences when we know that their entire process is a series of molecular mechanisms interacting on a neurological scale. Or does it mean nothing?
My answer: Just like staring into the abyss, it is inevitable that the study of one's own mechanical nature will disabuse one of particular notions. But it can also be empowering. Instead of striding blindly forward into society's absurdly condoned strange madness, aka love, one can grasp it with both hands and choose to manipulate oneself accordingly.
Do you want to fall in love with her. Then do this. And if you don't, well, you'd better stop what you're doing. Biology as a key to the Socratic imperative.
Which is all a very long way of saying: I choose to love you.