A good case can be made for our non-existence as entities.
LEWIS THOMAS
There’s someone in my head and it’s not me.
PINK FLOYD
I think I am me. But I am not. I am a galaxy. In fact, I am a thousand galaxies. There are more cells in my body than there are stars in a thousand Milky Ways. And, of all those myriad cells, not a single one knows who I am or cares.I am not even writing this. The thought was actually a bunch of brain cells – neurons – sending electrical signals down my spinal cord to another bunch of cells in the muscles of my hand.1
Everything I do is the result of the coordinated action of untold trillions upon trillions of cells. ‘I like to think my cells work inmy interest, that each breath they draw forme, but perhaps it isthey who walk through a park in the early morning, sensing my senses, listening to my music, thinking my thoughts,’ wrote American biologist Lewis Thomas.2
The first step on the road to discovering that each and every one of us is a super-colony of cells was the discovery of the cell itself. Credit for this goes to Dutch linen merchant Antonie van Leeuwenhoek. Aided by a tiny magnifying glass he had adapted from one used to check the fibre density of fabrics, he became the first person in history tosee a living cell. In a letter published in April 1673 in thePhilosophical Transactions of the Royal Society of London, van Leeuwenhoek wrote, ‘I have observ’d taking some blood out of my hand that it consists of small round globuls.’
The term ‘cell’ had actually been coined two decades earlier by the English scientist Robert Hooke. In 1655, he had examined plant tissue and noticed dead compartments stacked together. However, neither he nor van Leeuwenhoek realised that cells are the Lego bricks of life. But that is what they are. A cell is the ‘biological atom’. There is no life – as far as we know –except cellular life.
Prokaryotes: a protected micro-universe
The first evidence of cells comes from fossils about 3.5 billion years old. But there is more tentative evidence, from about 3.8 billion years ago, in the shape of telltale chemical imbalances in rocks that are characteristic of living things. The first cells, known as prokaryotes, were essentially just tiny transparent bags of gloop less than a thousandth of a millimetre across. The bag, by concentrating stuff inside, speeded up key chemical reactions such as those that generate energy. It also protected proteins and other fragile products of those reactions from toxic substances such as acids and salt in the environment. The bag of gloop was an island haven in an ocean of disorder and chaos, a protected micro-universe where order and complexity might safely grow.
The complexity of such cells was in large part due to the proteins – megamolecules assembled from amino-acid building blocks and made of millions of atoms. Depending on their shape and chemical properties, these Swiss-army-knife molecules can carry out a myriad tasks, from speeding up chemical reactions to acting as cellular scaffolding to flexing like coiled springs to power the movement of cells. Even a simple bacterium possesses about four thousand different proteins, though some proteins, such as those needed for reproduction, are assembled, or expressed, only intermittently. The structure of these proteins is encoded by deoxyribonucleic acid, or DNA, a double-helical molecule floating freely as a loop in the chemical soup, or cytoplasm, inside a cell.
Cellular structure is beautifully intricate. First, there is the bag, or membrane. This is made of fatty acids, molecules that are characterised by having a water-loving end and a water-hating end. When such lipids come together in large numbers – typically a billion – they spontaneously self-assemble i
