It’s curious how we can create a fate map, know what cells will form what limbs, nerves, brain and gut, when the ball of cells is only a few days old – so young its age is still counted in hours post-fertilization. That you can go “these cells here, they’re going to form the skin, and these here are going to form the brain” when all you have is a disc just three cells thick. You spend hours reading of dissections, scientists removing first this bit and then that, to see how the cells change their development – “if we remove this bit here, then turn it around and stick it back in, does it make any difference?” – and yet the first time you do it yourself, cut into an egg to remove the chicken embryo, you’re surprised how human it looks. Birds and humans and dogs and crocodiles all look the same at that stage, until the skeleton develops beyond the faintest suggestion of differentiating cells, the brain is more than one end of a darker line that traces the length of the notochord, the cells that aren’t nerves or muscles or even a mix of the two but just cells, parasites off another body and incapable of feeling.
The first time you remove an embryo from its egg, it’s a little blob. The next, you can define a head, here, and eyes – horribly out of proportion – and the faintest suggestion of a limb, not much more than a bump in the rounded comma that exsanguinates under your scalpel. You tell yourself that it can’t feel – it’s dead anyway, if it were to develop any more it would have horrific deformities; indeed the embryo in the next egg is slightly more developed, and if you look closely you can see the start of encephaly. But a tiny part of you twinges with guilt – that in order to learn how to save lives, you must first learn to end lives that never began, study their development under a microscope, dissect limb – with the first growths of bones faintly visible – from body to grow on in artificial fluids. Connect what you see to the pictures in the textbook of the adult dog – connect it to the cadaver in front of you leaking formalin into a bucket. Connect it to the hands in front of you, the bones arranged in an almost identical pattern; carpals to metacarpals to phalanges, no longer humanized but merely another anatomical study. Flex your wrist as you read, already correcting yourself to call it the metacarpal joint, trying to observe the sliding of tendon and muscle under skin, naming deep digital flexor and interossus muscle, knowing that the arrangement of the forearm in front of you is not so different from the dissected forelimb of a few hours ago.
And people wonder why I have such a sick sense of humour.