I often think about how effortless my life would be if I was a mouse; running between cupboards, shagging all the time and doing tiny poos. I would respond instinctively to my environment and never question or analyse. I wouldn’t need horoscopes or psychology. If something is scary, run away; if something smells nice, have a bite. Unfortunately, tens of thousands of years ago, my ancestors developed a complex awareness and intelligence that made responsive simplicity impossible for me. And for you.*

Here is a rough timeline of where we come from:

I’ve taken the approximate dates above from people who seem to know what they’re talking about/have written books with good Amazon reviews. But there are elements about which experts disagree, not to mention people who have a fundamental religious belief.† My ex-boyfriend’s mum used to say that evolution was ‘all a bit far-fetched’ and I used to laugh and laugh, which is more enjoyable than arguing with someone. I haven’t spent my life studying fossils, all my knowledge is secondary. If you prefer a different explanation for how human beings came into existence then you’re welcome to read the following as a fable and we can still be friends.

Evidence for the gradual shaping and sudden mutations of human evolution comes from our own DNA structure and skeletons¶ found underground. Scientists use recovered bones to find out about our ape and Homo relatives that are no longer around, and to trace our species’s physiological development from tree-dwelling, plant-eating idiocy up to our bipedal, less hairy, super-brainy current state.

I’d like to give you a compliment now: YOU ARE SO CLEVER. So clever. No matter how you did in your GCSEs, no matter how often you’ve forgotten where you put your tea and knocked it over, you are exceptional. You have a HUGE brain. It’s too big. It’s embarrassingly large. It’s proportionally massive, roughly three times bigger than an orang-utan’s or chimpanzee’s, twice as big as a gorilla’s. And it’s not just insanely huge, it is brilliant at communicating with itself. It’s adaptive. If you became blind as a child, your brain can map the world using non-visual spatial awareness. If you’re deaf, your brain reorganises to comprehend language via visual stimuli. If you’re a black-cab driver you’ll have a phenomenal, muscular memory while if you’re an alcoholic you’ll suffer protective blackouts. Our brains change how they function in order to be as efficient as possible according to how we use them. This process is called neuroplasticity and it takes place continually throughout our lives.

Your large and elastic brain allows you to interpret the world in a way that your ancient ancestors couldn’t. It was developed over thousands of generations as a survival tool, for mapping landscapes and predicting behaviours. For hunting and pretending and cooking and protecting. It makes empathy possible as well as the ability to manipulate empathy in others. From the second you were born, your brain has been collecting information in order to make you stronger and more prepared for whatever you might find in the world. Your brain interprets and encodes everything that happens outside and inside of you into what we call ‘meaning’. It translates vibrations into music, reflected light into scenery, the movements and vocalisations of other Homo sapiens into friends and enemies; it literally creates your world, and you alone live there.

As strange as it sounds, some of our brain’s ‘thoughts’ are unconscious. We all have instinctual impulses and these are inherited because they enabled our survival. A good example is hunger. No one needed to teach you to want feeding; your body responds that way because for millions of years the mammals who were impelled to eat periodically were far more likely to successfully breed than those malnourished losers who felt no impetus. You have the genes of the hungry. It’s inbuilt inside you, you’re pre-programmed. The conscious part of the brain is the bit that gets you fed. That’s how your ancestors knew where to forage, or how to track an animal. It’s how you manage to ask directions to the nearest supermarket and select a baguette filling you think you’ll enjoy.

Perhaps your conscious mind is working away right now, thinking, ‘UM, excuse me lady but I don’t actually feel hunger. I never know when to eat, I’d starve to death if someone didn’t tell me to have a banana occasionally—’

Well okay then you: throughout this book I will be making sweeping, generalised statements that are true for the majority of the human race. Not for everyone. There will always be exceptions and abnormalities. We are a very varied species; every generation displays a wide range of possibility. If we were all exactly the same, certain environments or circumstances would’ve wiped us out in our uniform unsuitability. The outliers and the unusual are our species insurance: curiosities and anomalies have enabled us to survive. So you’re unique and unusual, well done, now pop off and eat your banana.

The desire for sex could be called instinctual, it’s a—

Please don’t speak with your mouth full. For the vast majority of adult people, the desire to have sex appears as an instinct. No one has to sit you down and encourage you: ‘Look at that guy over there, doesn’t he have lovely arms?’ But with sexual instinct, the interplay of desire and its satisfaction is more complicated than having a sandwich or reheating lasagne. It involves other people, both as objects of desire and as possible sex partners. I cannot have sex with everyone I want to. I cannot have sex every time I feel the urge. I have to hide the majority of my sexual feelings due to social expectation, cultural education and politeness. We all laugh when a dog humps someone’s leg; his life is free of rules and shame. He does not ask himself, ‘Does this leg fancy me back? Will it be insulted or offended? Is it a married leg? Or underage?’ No, he jumps on and grinds away as his body instructs him. The dog can’t get the leg pregnant, so we can just laugh – what an idiot – but the instinct he’s obeying will mean sometimes that leg is another dog and puppies will be made. So it works, it’s a great system. The dog’s urges result in more dogs for the world, HOORAY!

Unlike a dog, you’ll have been taught about sex, whether in detail or implicitly. From your parents, school videos, watching Dirty Dancing when you were eleven and not quite understanding it, you’ll have absorbed a trillion messages about what sex is and how you are meant to feel about it. And now, my friend, you’re a tug-of-war. Pulled one way by your unconscious desires, pulled back and restrained by the rules of behaviour that your society and upbringing have foisted on you. Instinct on one shoulder, expectation on the other. Add this to the false construction of female sexuality that’s flung at you from porn, TV and women’s magazines and you’re all set for difficulty orgasming confusion.

You’ll have heard phrases about humans being a ‘higher’ species, but interestingly only from other...