One of two passages I want to quote from Michael Mayne's Learning to Dance. This is from the chapter entitled June: The Dance of DNA. One of Mayne's other books, This Sunrise of Wonder, has been a book I've gone back to at least twice, and it's still a great book to dip into. Learning to Dance is proving to be just as good.
I've altered the paragraphing to make it more readable on here.
In mid-December 1928, my mother became pregnant. Here again the combination of law and chance took effect: the law dictates that male sperm fertilise female eggs, while chance allows just one sperm (out of 300 million or more) finally to each and invade the ovum, some 85,000 times its own size. Around each one of us hover the shades of a million other lives that were not destined to be born. By early January a distinct tube-like structure had been formed in my mother’s womb: it would become my heart, and it was already beating. By early February the early forms of all my internal organs were present, though the embryo that was potentially me was only a little more than an inch long and weighed less than one-fifth of an ounce.
Already my genetic make-up had been determined. The genome (that sequence of genes which carries instructions for the manufacture of proteins) was directing the two hundred or more types of cells of which we are composed to their various ultimate locations in order to generate the necessary systems (skeletal, muscular, circulatory, reproductive, digestive, urinary, respiratory): to my lymphatic system which would fight disease; to my immune system whose role would be to distinguish friend and foe, what belonged to my body and what did not; and to my autonomic nervous system, that widespread web of nerve-cells, circuitry and chemicals with the task of preserving within my body both equilibrium and constancy.
In a few more days tiny arms and legs could have been seen, the hands and feet still paddle-like, with web-like bits between the fingers and toes, and faintly detectable ears and eye sockets. ("In the absence of any other proof," said Sir Isaac Newton, "the thumb alone would convince me God’s existence.")
My central nervous system and muscles had formed sufficiently to respond to gentle stimuli. Ever movement and change was now being choreographed by the genetic code, various cell groups uniting to
‘migrate, twist, turn, glide, fold, bend, lengthen, branch, fuse, split, thicken, thin, dilate, constrict, hollow out, form pockets, pinch off, adhere, separate….Hundreds of millions of dancers appear and they all participate, forming themselves into the shapes of various tissues and organs.’ [Sherwin Nuland in How We Live]
I had become a foetus, and it was all systems go.
By the middle of March my head was still enormous in comparison with my body. Fingernails and eyelids had formed, plus lips and an enormous nose. My ribs and vertebrae had become cartilage. By the middle of April my body was catching up with my head: I was some nine inches long and my mother could begin to feel me kicking. By the end of May, with an ear to the womb you could have heard my heartbeat, and I was beginning to show signs of an individual personality, establishing patterns of sleep and wakefulness. I was even growing eyelashes.
By Midsummer Day my eyes were complete and I could both hear and cry. Finally, on 10 September I was born. And already there was enough information capacity in every single cell in my body to fill some dozen copies of the Encyclopaedia Britannica.