Like a Virgin by Prasad, Aarathi (recommended reading txt) 📕

every cell type that exists in the adult, creating, over a series of cell divisions, a complete new individual – sometimes, in a matter of days. No other cell can match this feat.

A beautifully orchestrated concert ensues in an animal egg after fertilization occurs. Like a pool bursting with the elegant and energetic motions of a team of synchronized swimmers, molecules interact and cells cluster and move around to the very spot where they will be called upon to shape a new creature in early, miniature formation. Soon (in humans, about fifteen days later), the early embryo organizes itself from a simple ball of cells into an organism made up into what are called germ layers: the ectoderm (the ‘outer skin’ in Greek), the mesoderm (the ‘middle skin’), and the endoderm (the ‘inner skin’) in all vertebrates. These skins are literally the layers that build us, and are responsible for forming all the structures and organs present in a fully developed animal body. It is now that a recognizable body plan begins to be laid out.

The endoderm, the innermost of the three layers, forms a simple tube, which will eventually become the digestive tract, connecting the mouth to the anus. The tube will differentiate into parts as diverse as the pharynx, which helps us to speak; the oesophagus, the ‘entrance for eating’; the trachea, or windpipe; the salivary glands; the liver; the pancreas and certain glands of the pancreatic system; and even the lungs – the respiratory and digestive systems being intricately connected. The mesoderm gives rise to the muscular and fibrous tissues – the muscles, including the heart; connective tissues, cartilage, bones, bone marrow, blood, and the epithelia that line the blood vessels; the lymphatic vessels and lymphoid tissues; the reproductive organs and the urinary system; and the notochord, a column of tissue that bisects the embryo into left and right sides, and which later develops into the vertebral column. The ectoderm becomes the brain and spinal cord, via a process in which a part of the layer rolls up into a tube and pinches itself off from the rest. As it pinches off, some ectodermal cells escape into the mesoderm, where they form part of the nervous system as well as the pigment cells of the skin. The rest of the ectoderm envelops the embryo with what will become the epidermis – the outer layer of our skin – complete with sweat glands, hair, nails, and teeth.

An egg trying to make all this stuff on its own is up against a number of natural obstacles. For one, an egg has only one set of DNA, but its offspring requires at least two, to get that right number of chromosomes. Second, to start the process of separating, copying, and dividing up its chromosomes, the egg needs some centrioles – barrel-shaped cellular structures, provided by sperm, that help to move the chromosomes around during cell division. Third, at some point along the way to becoming an embryo, the egg will face the roadblock of metaphase II arrest. And for mammalian and marsupial eggs, there is a fourth challenge: evolution has locked some genes so they just won’t work for creating offspring. Still, some human eggs have gone solo – or perhaps it’s more precise to say that they have gone rogue.

The main evidence for the human egg’s capacity to develop on its own comes from teratomas – shocking, grotesque cell masses that appear to be an amalgamation of unfinished or discarded body parts. Mature teratomas are a rare form of benign tumour made up of varying combinations of ectoderm, mesoderm, and endoderm tissues. They have been documented in guinea pigs, dogs, cats, horses, marmosets, rhesus monkeys, baboons, and humans. Some teratomas are smooth, shiny balls of skin; others, a bloody fur ball of hair; yet others a lump of raw flesh spiked with perfectly formed teeth. Often, under their skins, they also contain organ systems and major body parts. It may not come as a surprise, then, that teratoma comes from the Greek for ‘monstrous tumour’.

Ovarian teratomas, which grow from egg cells, have been identified in girls as young as two and women as old as eighty-eight, but they mostly tend to develop in women in their twenties or thirties, or ‘late’ reproductive age. Studies of twins indicate that the propensity to develop ovarian teratomas may be inherited. These teratomas are quite distinct from the more highly developed growths known as fetus-in-fetu – malformed, parasitic twins that grow inside a living person’s body. Fetus-in-fetu are the product of normal conception, while ovarian teratomas come from eggs that have never had a whiff of a sperm cell. Essentially, they are unfertilized eggs that didn’t or couldn’t respond to the signals to stop and restart developing – the usual holding periods involved in readying an egg for reproduction.

The vast majority of ovarian teratomas recorded in humans have gone so far as to develop such features as skin, hair, and teeth. In twenty-four known cases, ovarian teratomas have contained a homunculus – a mini-human, or partial, foetus-like structure, something straight out of Paracelsus. The Latin term homunculus roughly translates as ‘a structure resembling a miniature human body’ and today is used by doctors to describe a growth of tissue that has the features of a human being but which was not produced by pregnancy.

In 2002, a twenty-three-year-old woman was admitted to the Korean University hospital with a huge lump in her pelvic area. It was soft to the touch, and it moved around when prodded. The patient had never been pregnant and had regular periods; her womb and her Fallopian tubes were normal. Doctors performed an ultrasound and found that, in fact, the woman had two lumps, one in each ovary. The masses were removed and dissected. Both had smooth, glistening surfaces and measured about fifteen