Dr. Armand Leroi, of Imperial College London, examines what makes us human and looks at a rare disorder that leads to not-quite-humans:
Travel the Grand Trunk Road between Lahore and Islamabad, and you come to the city of Gujrat. Awash in the smog and sewage produced by its million-odd inhabitants, it is an unlovely place best known for the manufacture of electrical fans. It is also the location of a shrine to a 17th-century Sufi Saint by the name of Shua Dulah. For at least 100 years, but perhaps for centuries, it has been, though is no longer, a depository for children with microcephaly.The word “microcephaly” comes from the Greek, “small head”. But in Pakistan, such children are known as chuas or “rat people”. The name is uncharitable but apt, for their sloping foreheads and narrow faces do, indeed, have a rodent quality. When I visited the shrine earlier this year, I found only one chua, a 30-year-old woman called Nazia. Mentally disabled — I would judge her intelligence to be about that of a one- or two-year-old child — her nominal function is to guard the shoes that worshippers leave at its entrance, but that work seems to be mostly done by her companion, a charming hypopituitary dwarf called Nazir.
These days, most chuas are intinerant beggars. Travelling up and down the Grand Trunk Road, following a seasonal calender of religious festivals. Each chua is owned, or perhaps leased, by a minder, often a raffish, gypsy-like figure. The Chua-master looks after, and profits from, his chua rather as a peasant might a donkey; together, they may earn as much as 400 rupees per day, about £4. Most people I asked supposed that there are about 1,000 chuas in the Punjab, but no one really knows.
Where do they come from?
There is, inevitably, a local myth to account for origins of the chuas. Infertile women, the story runs, come to the shrine to ask the saint to intercede on their behalf, to give them children. This he does, but only at a price: the first-born child would be a chua. That child has to be given back to the shrine where it would be raised, and live, as an acolyte. Should she fail to do so, all future children will be born chuas as well.
What is the real cause?
Disorders caused by recessive mutations are normally rather rare. But not in Lahore; nor in Leeds [which has a large Pakistani immigrant population]. That’s because of the Pakistani way of marriage. Most of us marry people quite distantly related to ourselves and, as we travel ever further, our mates become ever more genetically remote.In Pakistan, however, some 60 per cent of marriages are between first cousins; the frequency in Bradford and Leeds is thought to be comparable. The result is that clinical genetics units serving the British Pakistani community see a range and frequency of genetic disorders unknown elsewhere in the country.
Why is this more than a curiosity?
The discovery of genes that control the growth of the brain immediately suggested that these genes might also have changed in the last six million years since we last shared an ancestor with chimps. And so it proved: of the four microcephaly genes that have been found, three bear the hallmarks of rapid evolution. To be sure, chimps have versions of these genes, but the human version is different. So different, in fact, that their evolution must have been driven by natural selection.It is hard to understate the beauty of this result. Ever since Aristotle, philosophers have wondered: what makes us different from the beasts? What makes us human? The answers that they have supplied: that man is a political animal, a thinking animal, a naked animal, a tool-making, tool-using animal — answers that, for all the aphoristic pleasure they provide, are essentially meaningless if not blatantly false, can now be discarded.
Now, when we ask: “What makes us human?” we can answer: this gene and that one … and that one. We can write the recipe for making a human being. Or, at least, we can begin to.