Profitable Wonders
James Le Fanu
The mouse is seemingly the most inconsequential of creatures. Small and weak, the defenceless victim of a host of sharp-clawed predators, a synonym for the dull and unprepossessing, and the personification of timidity (are you a man or a mouse?).
And yet rarely has a reputation been so ill-deserved. After man, the mouse and its confrères are the most successful group of mammals on the face of the Earth, while revealing, in recent years, the profoundest insight into the mysteries of genetic inheritance.
Their diminutive size is actually their greatest asset. It allows Mus domesticus to make its home warm, secure and protected from the elements beneath the floorboards of our homes; moving freely through the narrowest of apertures as it forages for food behind the stove and within seemingly tightly closed kitchen drawers.
The mouse’s foraging skills are further enhanced by three most useful adaptations: first, a pair of manipulative, five-fingered forefeet, the most versatile in the animal kingdom, with which to pick up minuscule items of food; two self-sharpening, chisel-like incisors capable of biting through the hardest shell or husk; and, thirdly, an ironclad digestive system.
Mus domesticus is a true omnivore which will eat anything, not just the obvious (bread, biscuits, fruit, rice and chocolate) but also moths, old bones, candles, soap and plaster.
And she is famously, notoriously, fertile, producing up to ten litters a year of, on average, half a dozen offspring. She can conceive again within a day of giving birth and, in feeding her blind, naked pups, can reputedly produce sixteen times more milk every day, relative to her body weight, than a cow.
And mice are, in their way, intelligent, inquisitively exploring and colonising new territories, avoiding the traps laid for them and eluding, Tom and Jerrystyle, the attentions of the house cat.
So much then for the ‘wee, sleekit, cow’rin’, tim’rous beastie’ that, despite its humble status, frustrates all efforts to permanently dislodge its unwanted presence from our homes.
But there is more. For Mus domesticus also, and fascinatingly, illuminates with great clarity how little we truly comprehend of the most fundamental aspects of biology.
The combination of its small size and prodigious fecundity has over the past hundred years elevated the role of the mouse in human affairs to become the undisputed superstar of medical and biological research.
It is the ideal ‘model organism’, essential for the tens of millions of experiments conducted every year; assessing the efficacy and safety of drugs, investigating the mechanisms of diseases, and, most recently, deciphering how the genes strung out along the double helix ensure all forms of life replicate themselves with such fidelity from one generation to the next.
The genomes (or full complement of genes) of man and mouse, around 20,000 in all, turn out to be almost identical – differing by just one per cent. This might seem a bit surprising, but then we share, along with all other ‘higher’ organisms, the same basic machinery, the same cell types, the same hormones, proteins and enzymes that drive the cycle of life.
The profound differences between man and mouse must thus lie in the remaining one per cent, the ‘regulatory genes’ that control how everything is put together. Their function, it was hoped, would be elucidated by ingenious ‘transgenic’ experiments, introducing a regulatory gene from another organism into the mouse embryo and seeing what the effect would be.
The results are baffling. The same gene that orchestrates the formation of the mouse’s legs also, it turns out, instructs for the limbs of crustaceans, centipedes and chickens. The same gene that orchestrates the formation of the mouse’s camera-type eye gives rise to the fly’s very different compound eye. And so on.
There is, in short, nothing in the genomes of mouse and man to account for why the mouse should have four legs, elegant whiskers and a pea-sized brain; and why we should have two arms, two legs and a mind capable of speculating about the origins of the universe.
The genetic instructions must be there, of course, but we have moved, in the light of these extraordinary findings, from supposing those genetic instructions are at least knowable in principle, to recognising that we have no conception of what they might be.
‘The gap in our knowledge is not merely unbridged, but in principle unbridgeable’, observed professor of genetics Philip Gell, ‘and our ignorance will remain ineluctable.’