The Making of You. Katharina Vestre

      

       CONTENTS

       Preface

       The Race

       The Hidden Universe

       The Recipe for a Human

       The Invasion

       Natural Clones and Unknown Twins

       The Contours of a Body

       Cell Language for Beginners

       The Art of Building a Fruit Fly

       An Heirloom from the Ocean

       Fleshing Out the Plan

       Sex and Sea Worms

       Secret Preparations

       The Brain’s Inner Wanderings

       The Senses

       A Hairy Past

       From Water to Air

       The End – or The Beginning

       References

PREFACE

      WHEN I WAS six years old I collected hotel soaps, played with Barbie dolls and wore flashing sneakers. My taste in movies was exceptionally unoriginal and can be summed up as ‘anything with princesses’. But my favourite book? Pregnancy and Birth: A Practical Handbook for All Future Parents. My sister and I would take it down from the bookshelf, skim past all the dietary advice and stop when we reached page 70: The foetus as it grows. Fascinated, we would follow the illustrations of this tiny creature as it increased in size, thinking of our own brother-to-be curled up inside our mother’s tummy. We learned how he was transforming from a strange, primitive little animal with a tail into a chubby baby with arms and legs, confined in a space barely large enough to accommodate him. How was this possible?

      Seventeen years passed before I returned to this question. I was completing a bachelor’s degree in biochemistry at the University of Oslo, and sitting up late in the library one night, reading about cell biology. In my textbook was a series of images showing how a hand is formed in the uterus. At first it resembles a duck’s foot, and then the fingers gradually appear. In the caption I read that this transformation was due to mass cell suicide. Many years ago, all the cells that linked my fingers together died, on command from their neighbours, and left me with the hands I’m writing with now.

      This detail, I realised, was not included on page 70: The foetus as it grows. The pictures I’d seen as a six-year-old told only a small part of the story. How does this tiny creation actually come about? What happens in the cells, and in the DNA molecules? How does a hand know that it’s going to be a hand and not a foot or an ear, for example?

      In search of answers, I began digging through syllabus books and research articles. It wasn’t long before I became completely immersed. Prior to the summer vacation in 2015, I borrowed three huge embryology books from the library at Oslo University Hospital and took them with me on holiday to Italy. My internet search history filled up with egg cells and foetuses. Google drew its own conclusions and began showing adverts for baby creams (I don’t like to think what their algorithms made of my searches for fruit flies, fish kidneys and the gender development of sea worms).

      The result of all this was the book you now hold in your hands. It is a story about distant relatives, unknown twins, dangerous placentas and strange insects. And I can say right now – without giving too much away – that it is all about you. Let me tell you about the beginning of your life.

       Before we begin: a few words about time and size

      WHILE WORKING ON this book, I discovered that trying to state the age of a foetus is fraught with difficulty. There are various chronological calculations involved, and it’s not unusual for them to get mixed up. Doctors and midwives commonly use the week of pregnancy, which is calculated from the last menstruation. However, conception usually occurs about two weeks after this, so it’s not until a woman begins her third ‘week of pregnancy’ that she’s actually pregnant. In other words, the foetus is two weeks younger than the week of pregnancy: at the end of the twelfth week of pregnancy, the foetus is ten weeks old; at the end of the fourteenth week it’s twelve weeks old, and so on.

      I’ve chosen to use the conception as my starting point, so that all the time references I give reflect the real age of the foetus. Next, what is meant by a ‘month’? I have counted each month as a four-week period rather than a calendar month. Thus the first month comprises weeks one to four, the second weeks five to eight and so on.

      When I state the length of a foetus I mean the measurement from its crown to its rump. (You will sometimes hear this referred to as CRL, crown-rump length.) This measurement is preferred because the legs of a foetus are often bent upwards, making it difficult to establish its length from head to toe.

      Finally, please keep in mind that all time and size references are based on average values, and that every foetus develops at a slightly different rate. So, with that said, I think we’re ready to begin.

THE RACE

      IN THE HOURS preceding conception, a race begins that is almost impossible to win. A sperm cell starts out on an intense swimming trip. It looks like a little tadpole, battling wildly upstream against the current and in unknown terrain. It has several hundred million competitors. And it must swim a distance more than one thousand times its own body length. The rules are simple: reach the finishing line first, or die.

      The landscape around the sperm is confusing and inhospitable, an overgrown forest full of chaotic thickets and blind alleys. It risks being either swallowed up by immune cells or destroyed by acid on the way. It could also end up trapped in one of the deep crevices in the cervical wall. Before long, such hazards have eliminated most of the field, but our competitor is luckier: the woman’s muscle contractions help to push it upwards and it manages to enter the uterus.

      It is still a long way from victory. To have any chance of winning, it must first choose where to go next: right or left? The uterus is connected to two narrow channels – the fallopian tubes – and the finish line is at the end of one of them. The walls of each tube are lined with hairs that sweep fluid down to the uterus, but the sperm cell refuses to give up. It struggles on against the flow. Somewhere up there, hidden among the deep valleys and high peaks of the mucous membrane, a round egg is about to meet its champion.

      The egg cell has waited a long time for this moment. When the woman was a tiny foetus herself she’d already made the forerunners of her egg cells. Later on she began transforming them into mature egg cells. The cell now floating down her fallopian tube was one of the lucky ones. Each month, several egg cells start maturing inside every fertile female, but only one of them gets the chance to escape. The others face certain death.

      To create a mature egg cell, the forerunners divide so that the chromosome pairs containing the genes from the new foetus’s grandmother and grandfather are separated. At the end, each mature egg cell has half a set of chromosomes, some from Grandma and others from Grandpa, ready to find itself a new