The hurtle towards biological inevitability begins with attraction and lust. So what pulls us towards another person’s sweaty drunken body in the first place?

A huge range of things, as it turns out. Looks are one thing, especially for heterosexual men, but it really starts to get interesting when hormones become involved. The higher the levels of testosterone in both men and women, the more keen they are to get together, and what many people don’t know is that it can be transferred from the male to the female via the act of kissing. So, the more a female partner kisses, the more likely she is to want to have sex.

The nose also plays an important role in our sexual preferences. The reason you may like, or even love, someone, yet just can’t put your finger on why, can be down to their pheromones, which are odorless but recognized inside the nasal passages. This is because of the Major Histocompatibility Complex (MHC) found in pheromones, which confers your immunological status to the rest of the world.

Whether we like it or not, through our bodies’ natural instincts we are all looking (subconsciously) for mates with a different MHC to our own. This ensures that our offspring are immune to as wide a variety of pathogens as possible. In the small population of yesteryear, this instinct would have been vital to decreasing the chance of incest. If an individual’s MHC is too similar to their potential mate’s then attraction is diminished, reducing the chance of consanguine sex and genetic malformation.

Following lust is the Honeymoon Phase. This is regulated by neurotransmitters, which are chemical compounds that alter and modulate the signals in your brain. They are produced in the Caudus Nucleus region of your brain, to which blood flow increases when you first fall in love, in turn increasing neurotransmitter production. Mimicking the feelings you get from nicotine and cocaine, part of this process includes the release of dopamine. As an integral part of our bodies’ “reward” system, this neurotransmitter  is just so good that it is believed to play a significant role in addiction: hence all the clingy texts you get from your new beau.

If you are spending sleepless nights thinking about your love, then that is the adrenaline. It makes your heart race, causing insomnia and sweaty palms, which also explains the clamminess the first time you hold hands.

Upon falling for someone, an individual’s serotonin levels drop, sometimes to the levels of someone with OCD. Known as the neurotransmitter for pleasure, this may seem odd, but it accounts for the increase in anxiety and, depending on how well you can control it, the obsessive, never-ending texts.

The increased bloodflow to the caudus nucleus also affects the nearby prefrontal cortex, which is used for planning and preparation. These two areas of the brain work together to channel the passion from the dopamine affecting the caudus nucleus with the determination of the prefrontal cortex to obtain your goal: the love of your new partner.

After all of this we finally are able to reach attachment, and fully commit ourselves to love of both the body and mind. Oxytocin levels increase, cementing the relationship. (It is also released at orgasm, which is why it’s scientifically proven that  physical and emotional attachment are in proportion to one another.

It’s easy to forget that we are animals, and our emotions and feelings have become honed over millennia to make us feel the way we do for the benefit of us as a species. Sure, you have no control over your primal urges; but don’t panic – neither does anyone else.