The Science of Sex

The MRI Machine of Love (via Google)

Reproduction, biologically speaking, is the motivation for us all. As Shakespeare said, “all the world is controlled by the propagation of our genes and all the men and women merely players”. Or, something like that, right?

Anyway, from an evolutionary point of view, on this lovely planet we call home, the be-all and end-all of all life is to procreate. It’s what drives large mammals to tiny protozoa.

We all are just a slave to the ambition for immortal transcendence that only our genetic material can give us.

But, as in all of life, we humans like to think we are superior to the mindless drone of existence. We create art, we feel things. It’s an overwhelming ache –one that can be compared to that which Marburg victims feel when their intestinal epithelium sloughs off.


I have just finished reading The Hot Zone and have gotten a little carried away. (Pick up a copy, you will not be disappointed.)

In short, we human beings, with all our complexity and diversity, do not obey by the laws of nature.

We laugh in the face of them.

And perhaps we do.

More and more women forgo having children in the age of IUDs and autonomy over our bodies. More and more individuals on this planet are engaging in non-traditional relationships where the transfer of genetic information (to the end result of viable mini-humans) is not a reality — at least in the organic sense of the word.

But does that mean that the lonely cry from our DNA is not still echoing in the dank chamber of our cells?

Or, in the end, is it that elusive sexual gratification is our master and not this depth of our biological nature?

Are we in it for the momentary fleeting orgasm and not that lasting genetic immortality?

(Are you an aspiring science writer when you default type “organism” instead of “orgasm”? Yes, the answer is yes)

So, if we take a look at the sex drive of our species– away from the existential nature of continuing our lineage– what makes us hot under the collar? (Not lame sentences like that, that’s for sure.)

Let’s tip toe away from evolutionary factors by taking a look at the structures in our brain that create our reality.

The Four Fs and Dirty Dopamine

Brain Structures of Importance (Image via Google)

The Hypothalamus, the Thalamus’s smaller naïve brother, is a brain structure that is known for the oldest joke in biology, psychology and neuroscience a like.

It controls the Four “F’s” of evolution (stop me if you have heard this before) – Fighting, Fleeing, Feasting and Fu…Sexual intercourse.

The hypothalamus is part of our diencephalon – one of those fancy neuroscience words that describes our forebrain. This is a hop, skip and a jump away from our “Reptilian brain” or the seat of our basic autonomic functions – the brainstem. The hypothalamus, the wizard behind the curtain of our sexual desires, sits above the master of hormone secretion, the pituitary gland. (The pituitary gland happens to be the doppelganger of another hormone secreting organ that hangs much lower on the bodies of select individuals).

Now that we have oriented ourselves to this area of the brain – let’s turn our attention to an adjacent region – the basal ganglion. In the front seat of our basal ganglion we have the ventral striatum which houses the nucleus accumbens

All you are seeing are words and no meaning, right? I will break it down for you, don’t fret.

This whole area, of the Russian nesting doll that is our brain, is responsible for making up our so-called reward system. This area is often implicated in addictions and the neurobiological basis behind what makes people strive for another fix of their drug of choice.

Although, it is not all about outside substances. Certain stimuli can lead to a release of a cascade of chemicals in our brain. For example, that pleasure or reward system lights up like Christmas trees in December when one views porn inside an MRI machine. Yeah, you read that correctly.

A lot of that light show has to do with an endogenous chemical – a little neurotransmitter called Dopamine.

Dopamine is an excitatory neurotransmitter—meaning he likes to get the neurons aroused. Once excited, these neurons rain down action potentials, which are (to quote a neuroscience prof of mine) “the only currency we have.” Action potentials are what help us make sense of the world inside the sealed darkness that is our skull.

Dopamine is merely the messenger and he is responsible for a lot of other things beyond our reward system — like movement. A less than adequate amount of dopamine is responsible for movement disorders like Parkinson’s diseases and Parkinsonian like symptoms. (Perhaps dopamine’s greatest claim to fame is through L-DOPA and the lovely Oliver Sacks in the book and film Awakenings).

However, I am betting we are all familiar with dopamine’s dirty reputation in our reward system.

I like to refer to it as “The Dopamine Hit”.

That lovely, warm and satisfied feeling you get when excess dopamine is released inside your squishy friend. This often occurs when you have a positive encounter with someone you are attracted to. There is that one person (or perhaps multiple people) that really lend you a helping hand in that dopamine release. It is a tough animal to pin down, as that rewarding release can come in many forms: A dark glance from behind fluttering eyelashes or an unexpected touch – that brief fleeting moment of skin to skin contact. It could be something small, like a smile from across the room. Watching the smooth movement of their body as they walk away or hearing their voice at the other end of a line can get your dopamine buzzing.  Hell, even a response to a message that draws a smile to your lips – it does not take much to secure your fix.

Dopamine is insidious; his release can happen anywhere…even if we aren’t expecting it.

But it isn’t Dopamine’s fault – he has a job to do and that is it. The rest is our interpretation of his chemoelectrical Morse code. You perverts.

Love in the Shape of an Almond

Amygdala, our lovely “Almond” (Image via Google)

Now that we have explored the curves and cavasses of the reward pathway, lets touch on the limbic system– where we meet our friend the almond once more. ( I have spoken about him HERE)

The amygdala is a key player in the strange tingling feelings that we often try to ignore. Our emotional almond plays a role in associating emotional responses to key stimuli, along with stimulating some specific organs involved in arousal.

Ahem, is that your cell phone in your pocket or is your amygdala just happy to seem me? (I am so sorry. I could not help myself)

Back to porn and MRI machines. Studies have found that men respond more heartily to sexually explicit visual stimuli (the porn industry had the keys to that golden information for decades now) and that little almond may be the reason behind that.

The bigger the better it seems — even in terms of our brain structures. The amygdala has been found to be much larger inside the brains of males. It has also been noted that, when viewing sexually stimulating images, the activity measured by both the amygdala and our friend the hypothalamus was significantly greater in men than in women.

Much brighter fireworks went off inside the MRI machine of love.

Now, that we have a rough grasp of the structures and chemicals that play a role in our sexual responses, it appears that we are of more a slave to our neurotransmitters and grey matter than anything else.

It seems that we are compelled to seek out the attention of those people that provide us with that dopamine dump but what makes us attracted to these certain individuals in the first place?

It just might be microbes and compatible immune systems. Sexy, right?

Microbes and Immunocomplexes – Oh My.

Attraction is a funny thing.  We tend to be attracted to other people in a response to specific attributes they possess – so called “types.” This can be based upon visual and physical attributes or more esoteric traits like humour or intelligence. Sociology and Psychology has packaged attraction into neat little boxes and labels for us to consume.

You can be an sapiosexual and find intelligence overwhelmingly sexy. Perhaps you dig brunettes or people with a taller stature.

You could be heterosexual, homosexual, bisexual – sexual orientation we are all familiar with – but you could also be into mesophilia, or the attraction to middle-aged individuals.

As Lana Del Rey elegantly puts it in her masterpiece of musical composition, Cola, “I gots a taste for men who are older, it’s always been so it’s no surprise”

Lana Del Rey prefers the company of older men (Via Google)

But, is there any biological or scientific explanations for our sexual preferences? Well, it might all go back to our desire to find the perfect vessel to secure the continuation of our genetic lineage – in the case of heterosexual attraction, at least. (I tired so hard to get away from evolution, but he keeps pulling me back in).

In one study, woman expressed attraction to men that possess broad shoulders and muscular torsos, as apposed to more feminine looking male bodies. It was noted that even huskier individuals were marked higher on the attraction ladder. It came down to woman finding the illusion of strength an attractive quality. You can read that study, full of scientific rigour and bursting with robust quantitative data (so kidding) HERE.

Now let’s leave strong, masculine torsos behind for a minute and take a look at the cellular level.

There is another theory behind women’s attraction to a male mate – the immune system.

Remember the woman who can smell Parkinson’s? (HERE for your viewing pleasure) Well, in the same nostril as that idea, can we unconsciously pick up on immunochemical signals?

Seems a little out there, I must say, but let’s take a look at the literature.

Our Mate Compatibility Complex? (Via google)

Major histocompatibility complex, MHC, is a genetic component of the immune system across many species. The animal kingdom prefers mates with differing make up than their own. It’s all about that “securing the best possible progeny” thing I keep mentioning.

Variety is the spice of life and key to the successful continuation of your kind.

Animals pick up these kinds of things through olfactory cues and there is evidence that human’s can too.

In humans the MHC is referred to as the HLA (for human leucocyte antigen) and the jury is out on whether it is an aspect of our sexual behaviour. Women are the key players in the HLA game and appear to be more sensitive to picking up HLA related peptide ligands (fancy word for “molecules that bind to things”). Even though we humans lack the vomeronasal organ that other animals use to pick up on pheromones, it appears our olfactory cells are able to pick up on the subtle hints of the HLA. Like a fine wine.

In one study, the authors found that partners who had few similar HLA markers reported a more satisfied sex life than partners who had many HLA markers in common.

OK… So, those HLA related peptide ligands are what’s really responsible for that tachycardia I get when I see a man I am attracted to.

Some weird fetishes you have there Biology, but who am I to judge?

And lastly, we have fruit flies and microbes. Oh humble Drosophila, what wisdom can you bestow on us today?

Apparently, the microbes inside the fruit fly influence their sexual preference and can be manipulated through food. Flies given molasses diets prefer other molasses flies and this preference could be further manipulated with antibiotics. Once the flies’ bacteria were destroyed by the antibiotic treatment their sexual penchants disappeared and they became more promiscuous – choosing to mate with flies outside of their former food circle. This all came down to smell once more. The theory is that the presence of a specific bacteria altered sex pheromone production in the flies, creating their sexual quirks.

Remember the torsos? Well, that might not have been the out-of-place quirky anecdote it appeared to be. The illusion of strength tends to go hand-in-hand with higher testosterone levels in men. The higher the testosterone the theoretically more attractive the male. This, despite the fact that high testosterone levels can lead to some interesting traits — like anti-social behaviour and a higher rate of divorce.

The heart wants what the heart wants. And it appears to want, as my friend Vanessa so appropriately describes, “a vision of masculinity.”

Now, lets tie it all together – high testosterone levels in men are supposedly linked to stronger immune systems. The stronger the immune system, and the more diverse the HLA complex, the better the offspring.

We have come full circle and our hearts have been crushed by evolution once more.

Birds Do it, Bees do it, Even Blind, Bisexual, Polyamorous Geese Do it

But what about orgasms, you ask? Ok, well maybe you didn’t..but I sure did. The ever so sought after orgasm… truly this must be the reason we engage in the limb tangling activities we actively seek? Well, if you do a literature search on orgasms (please do) there is an exhaustive list of studies done involving its evolution.

Yeah, evolution again. Sorry.

The male orgasm plays an obvious role in this evolutionary affair, but the female orgasm is a little more esoteric. Theories range from mate selection to vestigial left-overs of our evolutionary journey.

Perhaps, we have all been tricked by our genes. As THIS ARTICLE so aptly put it:

 “What possible incentive could you offer your host to bring about that union? Try a somatic blitzkrieg of ecstasy, courtesy of the limbic system, the pleasure (as well as the pain) center of the brain. That’s orgasm.”

“Blitzkrieg of ecstasy” is the only way I am referring to orgasms from now on.

But what about love? We fall in love with people and this feeling can endure regardless of the expectation of our genes transcending through space and time. Right?

While you may be strongly attracted to someone, and possibly engage in physical fantasies when that dopamine hits your brain, chances are the appeal of that person extends beyond that. Perhaps you like what they have to say or how they think and just want to be around them.

Their presence makes you feel warm and tingly – and not in the way we have explored earlier.

As I said, we are humans.

We feel things.

We engage in partnerships for many different reasons, with many different kinds of people, because sometimes you just like being near them.

We will end with the story of Thomas, a blind goose, who fell in love with Henry a male swan. The couple lived together for nearly two decades before Henry partnered up with Henrietta, a female swan. But that did not discourage Thomas, who entered into a polyamorous relationship with the two swans. After another decade or so together Henry the swan died and Thomas was left alone. He went on to forge a relationship with a female goose and procreated. Thomas’ sham marriage to the female goose feel apart and his goslings were adopted by another male goose. Thomas was left to face the world alone again before succumbing to his increasing age (and perhaps a broken heart). You can read about Thomas HERE


Love is a hell of a drug.


This is your brain on porn
Ventral Striatum Activity
Where does Sex live in the Brain
Neurobiology of Desire. K. NeuroQuantology | June 2013 | Volume 11 | Issue 2 |
Sex differences in the Amygdala
Fruit flies
Gut Bacteria changes sexual preference in fruit flies
Influence of HLA on human sexual satisfaction
How Microbes Influence Your Love Life
Evolution of Orgasm

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