EACH OF US is a living library of historical information. We carry it around in every cell of our bodies. We use it to grow and develop and pass it on to our children. Thanks to science, we can use it to shed some light on who we are and where we came from. The information is of course the genetic data encoded in the sequence of chemical 'letters' that make up our DNA, the chemical blueprint of life.
This year has been something of a milestone for DNA. It was the year we celebrated the fortieth anniversary of the discovery of its double helix structure by Jim Watson and Francis Crick. It was the year of dramatic breakthroughs in medical genetics, with defective disease genes, such as Huntington's chorea, being identified at the rate of almost one a week, and gene transplants to cure inherited disorders beginning in Britain. It was the year that DNA shone light on the dead, from the fictional dinosaurs of Jurassic Park to the last Russian Tsar.
This demonstrates that genetics can tell us as much about history as about the present. Darwin started it all in 1859 with the publication of his then radical theory of evolution by natural selection. Gregor Mendel, an Augustinian monk whose pioneering work on the genetics of peas went unrecognised in his lifetime, took it a stage further with the establishment of genetics as a science. Now we are living in the golden age of 'molecular genetics'.
Words are a useful analogy for genes. Like words, each gene has a specific meaning and can sometimes suffer from errors - misspellings - that turn the genetic message into nonsense. However, such changes are not always bad. Like words, genes change over time and this mutation is the driving force for the evolution of life as well as languages. Just as Indo- European languages share common ancestors for some present-day words, such as those meaning royalty (raj, res, ri, roi, rey), human beings share common ancestors for the genes they possess today. Indeed, we share about 98.5 per cent of our DNA with our nearest primate relative, the chimpanzee.
Steve Jones tells the story of our genes better than most. His thoroughly enjoyable book (based on the BBC Reith lectures he gave last year) is scientifically authoritative yet personal, and has a wonderfully dark sense of humour.
'Genes and languages tell the same story about history,' he writes. If people speak different languages, they are unlikely to be on familiar terms, let alone get married and mix their genes. The genetic 'distances' of their descendants will tell the story. It is no accident that the Basques, whose language is not a member of the Indo-European family, have genetic distinctions from other west Europeans that mark them out as an isolated group of people.
The information stored in each of our genetic libraries is unique, yet intriguingly uniform. The genetic variation of present-day Africans is huge compared to non-Africans, indicating that homo sapiens spent much of its evolutionary history on the African continent, with only a small number of people (perhaps a 100 or even fewer) emerging from what is now the Middle East to populate the rest of the globe. Our genes tell that ancient story of migration, from the movement of the Celts in Europe, to the migrations of the Polynesians across the Pacific.
Yet no matter how ancient it is - thousands or hundreds of thousands of years - human history is still only a blink in time compared with the billions of years that DNA has been evolving on Earth. Jones's favourite metaphor for the history of life, and hence DNA, is the journey from Land's End to John O'Groat's:
Everywhere south of Birmingham is covered with primeval slime about which we know nothing. (Jones is a proud Northerner.) The first primitive land animals crawl ashore near Edinburgh. There are frogs in the Cairngorms and for thirty miles north of Inverness the landscape is infested with dinosaurs. Early primates appear near Wick, while our own species can look over the chilly water of the Pentland Firth from its birthplace a hundred yards from the northernmost shore of Great Britain. Recorded history begins on the beach, at high tide mark.
What happens between the sea and high tide is interesting enough - it occupies most of the book review pages each week - but the huge landscape beyond is equally fascinating. That story lies buried in our DNA, and Jones is one of the best storytellers around today.
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