The Mysterious Origin of the Sweet Apple
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The Mysterious Origin of the Sweet Apple On its way to a grocery counter near you, this delicious fruit traversed continents and mastered coevolution Barrie E. Juniper pples! You can find more than a and roses no fewer than fourteen.) vectors and that a female bee can forage Adozen varieties in the fruit section Does it have relations in the wild crab for up to three kilometers. of your local grocery, or spread out in apples of North America such as the Little wonder that there may be, a stall by a farm gate on a back road— garland tree (Malus coronaria) or in throughout the temperate world, per- maybe even in your own yard in au- Europe in the wild crab (Malus sylves- haps 20,000 distinct named apple vari- tumn. You’ll likely know the names tris)? Does it owe its size to some gross eties. There are, by contrast, only two of your favorites: Jonathan, McIntosh, chromosomal change like polyploidi- varieties of commercial banana and just Red Delicious. If you live in Western zation or a splitting or loss of existing one of the kiwifruit. Moreover, with al- Europe the selection might include chromosomes? Was it a chance discov- most no exceptions, every single apple Belle de Boskoop, Cox’s Orange Pippin, ery, like the kiwifruit, from a source pip has the potential to grow into a new Golden Delicious, Holstein or Ribston of nutritionally relatively indifferent apple tree—there are virtually no sterile Pippin. Abundant apples ready for the wild plants? The answer in every case apples. Elite apples from this genetic ka- eating can likewise be found in Eastern above is no, but the truth is perhaps leidoscope may be grafted to preserve Europe and on through Asia to the Chi- even stranger. their exact genetic character, but this is nese border and the Gobi desert. You Remarkably, the parentage of every not essential. Apple trees on their own can grow this delicious fruit, with its single one of the apple varieties list- roots are perfectly viable. On the other very high levels of vitamins and valu- ed above is unknown. Red Delicious hand, very many other commercial fruit able antioxidants, in your own back emerged by chance in an Iowa fence crops, such as navel oranges and com- lot in almost any soil; you can store it row. It was spotted in about 1870 and mercial bananas, are totally sterile and in the cellar throughout the harshest bulked up by the Stark Nursery Com- rely, eternally, for their genetic future of winters, and it will retain its flavor pany. Golden Delicious (no relation and spread, on grafting or some other and value into the early spring. You except that it’s an apple) emerged as form of clonal propagation. may cook it, dry it or ferment it as you a chance seedling, in about 1890, in a choose, but it is one of the very few hedgerow in West Virginia. It gained a The Geological Framework food sources that you can pick, ripe particular claim to fame by being cloned Long ago, probably some time between from the tree, and eat without any into millions of grafted young trees by the end of the Cretaceous and the early preparation, peeling, grinding, hulling the officers of the Marshall Plan, and Tertiary period (about 65 to 50 million or other manipulation. exported, after 1945, to revive the fruit years ago), the ancestors of the apple But what is this valuable and versa- industry of Western Europe. Figure 1. Apples are so ubiquitous that we tile fruit, and where did it come from? It seems that many of our favorite may be tempted to take them for granted. Yet Is it the product, like so many plants, apples have arisen by sheer chance. So their diversity and broad geographic distribu- of the hybridization of numerous par- what is the arithmetic basis of this lot- tion actually pose fascinating scientific ques- ents from distant lands? (Wheat has at tery? The secret to the apple’s origin tions. Why are there perhaps 20,000 varieties least three parents, strawberries two lies in the fact that apple trees cannot of apples but only two commercial varieties normally pollinate themselves. Unlike, of bananas and one of kiwifruit? Is the sweet Barrie E. Juniper is Emeritus Reader in plant say, peaches, which can and do self-pol- apple related to the so-called crabs? Were cur- sciences at the University of Oxford and Fellow linate, predictably producing peaches rently important commercial varieties—Red Emeritus of St. Catherine’s College, Oxford. His virtually identical to the parents, the vi- and Golden Delicious, for example—de- research has included explorations of plant sur- able seeds (or pips) will produce apples, veloped by hybridization or chromosomal changes? For that matter, where in the world faces, including the specialized ones of insect-eating some of which may have value—but carnivorous plants, and the interactions between did the apple come from? The author’s probe people, their animals and the evolution of crop none of which will resemble the par- of these and other mysteries of the apple’s plants. He and his coauthor, David J. Mabberley, ents. Imagine the evolutionary power origins takes us to a remote mountain range recently published The Story of the Apple (Tim- of the multiplicity of potential crosses in central Asia and introduces us to power- ber Press, 2006). Address: University of Oxford, in planted or wild orchards. Then mul- ful evolutionary drivers such as the bear and Oxford, OX2 6JF, U. K. Internet: barrie.juniper@ tiply this potential by the fact that a horse. (Photograph courtesy of Keith Weller/ plants.ox.ac.uk range of bee species may act as pollen USDA Agricultural Research Service.) © 2007 Sigma Xi, The Scientific Research Society. Reproduction 44 American Scientist, Volume 95 with permission only. Contact [email protected]. © 2007 Sigma Xi, The Scientific Research Society. Reproduction www.americanscientist.org 2007 January–February 45 with permission only. Contact [email protected]. UZBEKISTAN KAZAKHSTAN MONGOLIA to emerge as a distinct geological fea- TIAN SHAN ture about 12 million years ago, and it is still lengthening and rising. In places, in TAKLAMAKAN those “heavenly mountains” (that is the DESERT translation), if you stand in one place, you may be 1.5 centimeters higher at FERGANA CHINA Xi’an the end of the year than you were at the VALLEY beginning. The Tian Shan has by now lifted its peaks well above the snow Shanghai line and lies as a great mountain range about 1,600 kilometers miles long and 640 kilometers in depth, running from what is now China in the east to Uz- bekistan in the west. The east-west ori- entation, with about 20 parallel ridges, is important to our story. The vast mass of the Indian Ocean to the south, through the constant Figure 2. Ancestors of the sweet apple probably crossed a land bridge between North America warm monsoons, has kept the region and Asia, settling into central China near what is now the city of Xi’an. A few million years ago, these neo-apples made their way westward into the Tian Shan range. Red lines are trade ice free. The warming influence of routes along which the apple later spread. these monsoons, in due season, can be detected deep into China. Unlike migrated west across the land bridge tral China, roughly in the area of the the continental regions of northern Eu- connecting what is now North America current provinces of Xi’an and Shaanxi, rope and North America, the whole of with Asia. Although the Bering Strait and perhaps in a great corridor of Ter- the Tian Shan and regions to the south is currently a shallow sea with many tiary temperate forest, a recognizable have not, at least in the immediate geo- islands, during at least 12 periods in ancestral apple. logical past, suffered glaciation. Large the immediate geological past, seawater Much earlier, about 40 million years continental areas, as anybody who has was locked in glaciers and ice sheets, ago, the Indian subcontinent, which spent a night in the desert will testify, and the two continents were connected had detached from East Africa, crashed lose heat very rapidly. Thus northern by an ice-free bridge. Plants and ani- into the great northern land mass. Just Europe and North America chilled out mals would have moved, in both di- like something pushing gently on the rapidly along the advance of the ice rections, through “Beringia” to their edge of a carpet, this thrust successively fronts, as, time after time, the glaciers present locations. This little neo-apple drove up the Himalayas, the Pamirs moved deep to the south. would probably have looked more like and the Tian Shan. India is still moving As a result of its “defense” by the a hawthorn (Crataegus) with bunches northward at several centimeters a year, warm Indian Ocean over millions of of long-stalked fruits not much bigger as the mountain peoples of northwest years, the Tian Shan has become a than peas. But by about 10 million to India, Kashmir, Afghanistan and Ta- refuge for the sustained evolution of 12 million years ago there must have jikistan know full well. The Tian Shan, plants and animals. Almost no other existed somewhere in what is now cen- the last of the ripples as it were, began area in the world has remained invio- late for so long. In contrast, most of North America and the British Isles and much of Western Europe were scraped clean by ice little more than 10,000 years ago.