by Steve Jones
A few societies once encouraged matings with outsiders. In the Ottoman Empire, talented people were produced by promoting marriages between people from different nations. Their children were seen as 'the fruit of the union of two different species of tree; large and filled with liquid, like a princely pearl1. In South America after the arrival of the Spaniards there was what the invaders described as 'the conquest of the women'. Paraguay — the site of Elisabeth Nietszche's failed genetical experiment — was known as the Paradise of Mohammed, and every Spaniard had twenty or thirty Indian women. The Governor excused this, saying that 'the homage rendered to God in producing mestizos [children of mixed race who were raised as Christians] is greater than the sin committed by the same act'.
Outbreeding is not usually due to deliberate policy. Most of it arises, like so many of the biological events that shape the human condition, as a by-product of social change. Cities and transport play a central part as each provides a larger pool of potential mates than was available in the days of rural solitude.
In the Aeolian Islands off the coast of Italy in the 1920s a quarter of marriages were between first or second cousins. The figure has dropped to one in fifty (and in Italy as a whole is now less than one per cent). Britain, with its lack of a peasant class settled on its own land, has always been more outbred than most of Europe, but increased outbreeding can be seen here, too, with a striking drop in cousin marriages since Victorian times.
Elsewhere, the picture is not so simple. Some societies promote marriages between relatives for economic reasons. They are still frequent in Indian villages, where up to half of all unions may be of cousins, or of uncle with niece. Indeed, among Pakistani immigrants to Britain the incidence of cousin marriage is greater than in their native land, perhaps because of social isolation. Almost half of British Pakistanis of reproductive age are married to a cousin, a proportion higher that among their own parents.
A crude but effective measure of how related one's own ancestors may have been is to ask how far apart they were bom. If they come from the same village they may well be relatives, but if they were born hundreds of miles apart this is much less likely. For almost everyone today the distance between the places where they and their own partner were born is greater than that separating their parents' birthplaces. In turn, modern fathers and mothers were almost certainly born further apart than were their own parents. In nineteenth-century Oxfordshire the average distance between birthplaces of marriage partners was less than ten miles. Now, it is more than fifty. In the United States it is several hundred, so that most American couples are almost unrelated. All this shows how much the world's populations are beginning to merge. The most important event in recent human evolution has been the invention of the bicycle.
It will take a long time before the mixing is complete: an estimated five hundred years to even out the genetic differences between England and Scotland — and perhaps even longer to get rid of their cultural contrasts. Although homogeneity is a long way away, movement is bound to have an evolutionary effect. No longer will large numbers of children have two copies of a defective piece of DNA because their parents are related. Think of a sexual encounter between an African slave and a white slave-owner in early America. Each has a chance of carrying one copy of certain damaged genes. The most common error in whites is cystic fibrosis, in blacks sickle-cell anaemia. Only children who inherit two copies of either will suffer from inborn disease. Because cystic fibrosis is unknown in Africans and sickle cell in whites the child of a black-white marriage is safe from both.
In many parts of the world immigrant communities are merging with the people already there. Imagine that a tenth of the population of Britain were to immigrate from West Africa (where one person in fifteen is a carrier of the gene for sickle-cell anaemia) and to mate freely with the locals. The number of sickle-cell carriers in the next generation in the new mixed British population would go up by seven times. The incidence of sickle-cell disease (which demands two copies of the damaged gene, one from each parent) would drop by ninety per cent compared to the previous situation in the two groups considered together. Most children would be born to parents from the two different peoples, one of whom — the British partner — does not carry the sickle-cell gene. The incidence of the indigenous British problem, cystic fibrosis, would drop by a sixth.
This model of race mixture is simplistic but not unreasonable. In Britain now, about one marriage in thirtyis between two people of non-European origin; but a third as many is between a non-European and someone whose ancestors were born in the British Isles. The genes of Black Americans are evidence that there has been mating between Americans or African and of European origin for several hundred years. The effect will be more rapid in Britain, where inter-racial marriage is much more acceptable than it is in the New World. Such shifts may mark the beginning of an age of genetic well-being. Increased outbreeding means that recessive genes will more and more be partnered by a normal copy that masks their effects. Social change will dwarf the efforts of scientists to improve genetic health. In time the mixed populations will reach a new equilibrium and many of the hidden genes will reappear, but this will take thousands of years.
Accidental evolution has shaped the genes of small and isolated populations such as the Boers in South Africa and the inhabitants of Tristan da Cunha. In this new mobile world the chances of a small bottleneck and evolution to happen by accident are small indeed. The third part of the Darwinian machine — random change — has, like the other two, lost most of its power.
The great evolutionary fact of the past three centuries has been the population explosion. By the time of the Pilgrim Fathers, the population of the world was twice that on the first Christmas Day. Since then numbers have increased to reach their present six billion. For all creatures, evolution is a slower process than are shifts in distribution or in abundance. Many species go extinct before they have a chance to react to an ecological challenge. For ourselves, some ecological disaster (probably an Einsteinian bang rather than a Malthusian whimper) may mean that speculation about any genetical future is irrelevant.
That future, if it does arrive, will be influenced by local variations in the rate of population growth. Improvements in health care — and a subsequent increase in population number — always precede a decrease in the number of children that parents choose to have. The delay explains the recent explosion. Claims that the world population will double within a century have proved too alarmist. In most places the shift to the new world — a few, healthy children — has taken place more rapidly than even the most optimistic projected.
In the Pilgrim Fathers' day, European genes gained from population growth. Whites filled the world, while black and Asian numbers stayed more or less the same. Now, the equation has shifted. Growth is at its most rapid in Africa. Most European nations, indeed, are not sustaining their own populations, with the mean number of children per family in Italy and Spain well below replacement level. More than ninety per cent of growth is in the developing world, most of all in Africa. The United Nations estimate that more than ninety per cent of the population rise will be in these regions. Africa shows little sign of a decline in birth-rate. The number of children per woman in East Asia decreased from 6.1 to 2.7 between i960 and 1990; but in Africa the figures for those years were 6.6 and 6.2 A third of the globe's population may be of African origin by 2050. The AIDS spectre casts some doubt on this figure, but any difference in the relative rate of growth of distinct groups itself means evolutionary change. In the past — during the agricultural revolution, for example — increased numbers led to mass migration. In spite of the political barriers to movement in the modern world, future Utopians may be brown.
Nevertheless, most social changes are conspiring to slow down human evolution. Mutation, selection and random change have all lost much of their power. As a result, the biology of the future will not be very different from that of the past. Axonomic advance and medical progress may even mean
that humans are almost at the end of their evolutionary road, as near to the biological Utopia as they are likely to get. Fortunately, nobody reading this book will be iiround to see if L am right.
From the reviews
'A swashbuckling romp though a subject that normally delights only in its technical opacity.'
Richard Horton , Literary Review
'In literate and highly readable style Jones explains genetics and uses it to take us on a tour of human existence.'
a. c. grayling, Financial Times
'An inspired grand tour of what genetics can and cannot tell us about ourselves and our evolutionary history. wittily written.' david con car, New Scientist
This urbane, inrelligent and informative book deserves to be read widely, since it provides a vivid demonstration of what a remarkable and fragile product of evolution our species is.'
Christopher wills, Nature
'Very wiity, very accessible and very smart' Bite 'A witty tale of curious mutations, molecular clocks, and genetic bottlenecks; it illustrates biological principles with memorable examples from everyday life.'
DOROTHY bonn, Lancet
'In an age of genetic rriumphalism, Jones is that rare thing — a geneticist who is modest about his subject.. Though ultimately optimistic about the potential of modern genetics, the book disarms sceptics by repeatedly warning of the dangers of over-selling molecular biology as a cure-all for human ills.'
john durrant, Observer
'Jones is one of the best storytellers around today. His thoroughly enjoyable book is scientifically authoritative yet personal, and has a wonderfully dark sense of humour.'
STEVE Connor, Independent on Sunday
'Jones thoroughly demolishes the old myth that human races are distinct genetic entities, arguing that there is almost as much variation between neighbouring countries as between races.. The nature-nurture debate also receives an infusion of sense, this time with the help of the Siamese cat. Ask Jones whether the cat's coat is the work of nature or nurture and you are likely to be told, with more than a hint of exasperation, that the question is meaningless.'
Stephen young, Guardian
'Few scientists write well for a general audience, but Steve Jones is exceptional.'
beverley anderson, Books of the Year, Observer
'Good science for thinking people, wide-ranging and informa tive.'
A.s. BYATT, Books of the Year, Daily Telegraph STEVE JONES
The Language of the Genes
Biology, History and the Evolutionary Future
Revised Edition
Flamingo
An Imprint of HarperCollinsPublishers 77–85 Fulham Palace Road, Hammersmith, London w6 8jb
www.&eandwater.com
Fully revised edition published by Flamingo 2000 5
First published in paperback by Flamingo
with amendments and supplementary bibliographic essay, 1994
Reprinted nine times
First published in hardback in Great Bnuin by HarperCollinsPublishers 1993
Copyright © Steve Jones 1993, 1994, 1000
Steve Jones asserts the moral right to be identified as the author of this work.
Author photograph by Sally Soames ISBN 0 OO 655243 9
Set in Linotype Sabon by Rowland Phototypesetting Ltd, Bury St Edmunds, Suffolk. Printed and bound in Great Britain by Clays Ltd, St Ives pic
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission.
This book is sold subject to thVcemdftion that it shall not, by way of trade or otherwise, be lent, re-sold, hired out or otherwise circulated without the publisher's prior consent in any form of binding or cover other than that in which it is published iitul without.1 similar condition including this condition being imputed on the subsequent purchaser. To my parents and my brother who share my genes and my affection
A fully revised edition of the classic work on modern genetics, updated to coincide with the new map of human DNA, cloning, and genetically manipulated foods.
'Not so much divination as demystification… Aim attempt to bring genetics and evolution more into the public domain. If, for instance, you ever wondered just what genetic engineering is about, here is as good a place as any to discover. Few have Jones's ability to communicate a difficult idea with such humour, clarity, precision and ease.fe LAURENCE HURST, Times Higher
Appendix A BIBLIOGRAPHIC SKETCH
Trying to keep up with the scientific literature is like running up a down escalator. However much one reads, more and more is published until at last one is forced to give up from mere exhaustion, to be plunged into the Basement of Ignorance. Genetics moves so quickly that it is necessary to sprint upwards to stay in the same place. Although the fundamentals of the subject have not changed, many of the discoveries described here — cloned sheep, the complete human DNA sequence, and much more, were made in the late 1990s and the early months of the millennium.
Papers at the cutting edge soon go out of date. With the exception of a few key research papers, I have not tried to refer to all the sources used in writing The Language of the Genes. For those with access to a library, the British journal Nature and its American equivalent Science publish almost every week new discoveries in human genetics and evolution, accompanied by reviews that put the findings into context. Scientists used to read them from the back (where the job advertisements are). It is a sign of the excitement of genetics that more and more now study Science and Nature as they are written, from the first to the last page.
Human genetics has many specialist journals. The pace setter is The American journal of Human Genetics. The Annals of Human Genetics and Nature Genetics are aiso important. The American journal of Physical Anthropology approaches human evolution from a less genetical angle. New Scientist and Scientific American provide up-to-date information on genetics and evolution, published almost as it happens. Sometimes, even the newspapers get it right.
Genetics and evolution have inspired a number of outstanding books. One of the best is The Rise and Fall of the Third Chimpanzee by J a red Diamond {Vintage Books, London, 1992. and HarperPercn-nial, New York, 1993). His title comes from the discovery that chimps and humans share most of their DNA sequences. Diamond uses this to build an engaging history of what we can learn about ourselves from our living relatives. A more sedate account of human genetics is in The Code of Codes: Scientific and Social Issues in the Human Genome Project, edited by D.]. Kevles and L. Hood (Harvard University Press, Cambridge, Ma., 1991). Matt Ridley's Genome: The Autobiography of a Species in Twenty-Three Chapters. (Fourth Estate, London, 1999) is up to date and comprehensive, taking our chromosomes one by one. John Avise's 1998 book The Genetic Gods: Evolution and Belief in Human Affairs (Harvard University Press, Cambridge, Ma.) covers a wider field and puts it into a humanistic context. For a more pessimistic view of the subject's possible dangers — which may perhaps have been downplayed in my own pages — there is Perilous Knowledge. The Human Genome Project and its Implications by Tom Wilkie (Faber and Faber, London, 1993). Richard Lewontin lives up to his title {Biology as Ideology: The Doctrine of DNA, Penguin Books, London, and HarperPeren-nial. New York, 1993) w'tn a provocative onslaught directed at the self-righteousness which once pervaded much of human genetics. The confidence of the early geneticists was quite misplaced and Lewontin argues that the same is often true today.
Those not put off by scientific terminology — and genetics is plagued with jargon — should try Mange, E.J. and Mange, A.P (1998) Basic Human Genetics (Sinauer, Sunderland, Ma.), Strachan, T. and Read, A.P. (1999) Human Molecular Genetics (Wiley) or, for a comprehensive treatment, Vogel, F. and Motulsky, A. G. (1997): Human Genetics — Problems and Approaches (Springer-Verlag, NY). A wealth of internet links leads to aspects of modern genetics. The main data-base for inherited disease is OMIM (On-Line Me
ndelian Inheritance in Man) at http: llwww3.ncbi.nlm.nih.-gov.8o/Omim/. It contains an encyclopaedic, up-to-date and highly technical account of human inheritance. The Human Genome Project has its own web-page at http://www.nhgn.nih.gov./HGP/wh'ich is matched by a British equivalent from the Sanger Centre in Cambridge: http://ivebace.sanger.ac.uk.
My own jointly-edited book The Cambridge Encyclopedia of Human Evolution (eds. Steve Jones, Robert Marrin and David Pil-beam, Cambridge University Press, 1992) has articles on human and primate palaeontology, comparative anatomy, anthropology and genetics. Many of these subjects are covered in more depth by How Humans Evolved by R. Boyd and J.B Silk (W. W. Norton and Company, 1997) and Principles of Human Evolution: A Core Textbook by R. Lewin (Blackwell Science, Oxford, 1998). For engaging tales about evolution and its eccentrics one can do no better than The Encyclopedia of Evolution by Richard Milner (Facts on File, 1990). I have used language as a metaphor tor evolutionary change and The Cambridge Encyclopedia of Language by David Crystal (Cambridge University Press, z"'1 Edition, 1997) is a witty and complete introduction to linguistics for readers who, like me, come from outside the subject.
For those who wish to pursue further the points raised in individual chapters, the following list may be of some help. It is far from exhaustive and, because of space constraints, many topics covered in the text are not referred to here.