In an incredible BBCiWonder series, you are taken on a timeline of the various actions that came together to form you.
How one out of 250 million of your father’s sperm cells got the treasured prize – your mother’s egg; whether you would be named Amina or Babatunde; to the first real test you had to pass – not for promotion to the next class! – but for your ultimate survival; the actions that determined your unique set of fingerprints; whether you will be teased for being a leftie; and the kind of people you would find attractive.
Want to take the journey to find out the path you traversed for the first 14 weeks after that magical meeting between Mr Sperm and Miss Ovum? Let’s go!
Day 6: Your First Test Passed
At six days old, when you were just a clump of cells, you faced a critical test.
Already transferred to your mother’s womb from the fallopian tubes, to continue to develop, you needed to implant yourself into your mother’s uterine lining. But mothers have high standards – an embryo must be healthy to be worth nourishing for the next nine months. Around two-thirds of embryos fail at this stage or soon after and are lost, often before their mothers know they existed.
But because you are special, in your case, your cells released the chemical signal that showed they were developing properly, and you were assigned a legitimate space in your mother’s womb, and you assumed your rightful place.
Week 4: Your Facial Features Formed
Over the next few weeks, your face blossomed into shape as 14 different structures came together to make several complex intricate layers of tissue. Human faces all share the same structures, but no two faces are exactly the same. Your face was the result of your genes, and the precise timing of when they were switched on during this critical process. Scientists think there could be hundreds of switches in your DNA that carefully and subtly choreograph the making of our features.
Week 11: Leftie or Rightie? Determined.
Your limbs had developed by 11 weeks and you began to move and flex them. You were beginning to favour one side over the other. You might have begun to stretch one arm more than the other, or go on to suck one particular thumb. Nine out of ten foetuses become right-handed, one out of ten choose the left, and fewer than 1% are ambidextrous – equally comfortable using both sides. The preference you developed is thought to be largely down to your genes.
Week 12: Your Own Unique Identity – One fingerprint in 7 billion
The layers of skin around your fingers began to wrinkle, pushing against the amniotic fluid surrounding them. This interaction with your environment helped mould a unique combination of arches, loops and whorls in your fingertips.
Even identical twins experience slightly different pressures from the amniotic fluid and develop subtly different patterns. By 17 weeks, you had a set of 10 fingerprints that would distinguish you from the seven billion other people in the world.
Week 14: Predicting Who You Might Find Appealing
As your body was taking shape, you were also developing a signature immune system inside your body.
By 14 weeks you were making human leukocyte antigen (HLA) proteins, which help your immune system recognise bacteria and viruses. There are thousands of possible combinations of HLAs – you inherited your set from your parents. One theory suggests that HLA proteins change our aroma to other adults, and that we choose a sexual partner with a very different HLA makeup, and therefore smell, to our own. So your immune system developed before birth may have some surprising effects later in life.
Watch this page for the concluding part of the series.
