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Fruits and Vegetables
Outline This stuff is scattered in the book. Pp. 92-101 pp. 44-47 Tomato Apple Citrus Brassica Banana Carrot Onion Squash and Melon Tropical Fruits
Fruits: Botanical and Popular Botanically, a fruit is the ripened ovary wall. The ovary is part of the carpel, the innermost whorl of a flower, the female reproductive structure. The ovary contains the ovules, the haploid equivalent to mammalian eggs. Some fruits also contain parts of the flower base. Botanical fruits can be classified as fleshy, dry dehiscent, and dry indehiscent. Most of what are popularly called fruits are fleshy fruits. The generally understood common definition of a fruit is sweet and aromatic fleshy plant products that are mainly eaten as dessert or a first course in a meal, and not as the main meal. Thus, many fleshy fruits (in a botanical sense), such as tomato and cucumber, are considered vegetables in popular culture. In botany, a vegetable is simply any plant or plant part. In the common definition, vegetables are plant products eaten with the main course. In taste, they are salty or sour or savory, but not sweet. Some vegetables are botanical fruits: tomatoes and cucumbers for example. Others are plant stems, leaves, and roots.
Legal Fruits Botanically, a fruit is an ovary that has ripened after fertilization. However, in 1883 a 10% duty was placed on all vegetables being imported into the US. John Nix, an imported from New Jersey, argued that he shouldn’t have to pay the duty on tomatoes, because botanists consider them fruits. The case went all the way to the Supreme Court (which means at least 3 separate courts examined the question). In 1893, the Court ruled that for legal purposes, tomatoes were a vegetable, not a fruit. Based on popular usage: vegetables (including tomatoes) are eaten at dinner, while fruits are sweet and are eaten at dessert. Tomatoes are the state vegetable of New Jersey. Ohio considers tomatoes to be the state fruit. In Arkansas, tomatoes are both the state vegetable and the state fruit (indecisive).
Tomato Fight! In Spain, they have an annual tomato fight
Tomatoes The tomato is a New World crop, native to the west coast of South America and first domesticated in Mexico. It is in the Solanaceae (nightshade) family, as are potato, chile pepper, tobacco, and petunia. Species: Solanum lycopersicum, but until recently Lycopersicon esculentum. Brought back to Europe and to Asia (initially to the Phillipines) by the Spanish. It grew well in the Mediterranean climate and quickly caught on there. Many varieties. A big distinction: determinate vs. indeterminate. Determinate tomatoes flower and set fruit all at once, and have a sfixedsize. Bush tomatoes, favored by commercial growers. Indeterminate varieties are vine types, which contnue to flower and set fruit until killed by a frost. Favored by home growers.
Tomato Stories Lycopersicon means “wolf peach”, because it is related to deadly nightshade. Some thought it could be used to generate werewolves: this was an old German legend about nightshade, which Linnaeus borrowed when he named the species. It was thought to be poisonous in Britain and America, despite being eaten in large quantities elsewhere. In 1820, Colonel Robert Gibbon Johnson stood on the steps of the Salem Massachusetts courthouse, in front of 2000 people, and ate an entire bushel of tomatoes to prove that they weren’t poisonous. He survived. The local band played a mournful dirge as he ate, because they were sure he would soon die. This story may not actually be true: the first account appeared in print in 1906. It was dramatized in an early television series called “You Are There”, in 1949. First varieties to reach Europe were yellow, not red. In Italy they were called pomo d’oro (golden apple). This may have been mistranslated into French as pommes d’amour (love apple). Some thought they were aphrodisiacs (one of the eternal quests of humankind).
Tomato Pollination The wild plants are self-incompatible: they must be outcrossed to produce seeds and fruit. To facilitate this, the female parts extend well beyond the flower, and the stamens stay enclosed within the petals. The native pollinator, a small bee, didn’t move with the plants to the Old World. Selection for self-fertility was very useful. However, the anthers shed pollen very slowly, and is aided by the wind or the wing motion of bumblebees. In the greenhouse, a vibrator is used (the “electric bee”). This is called buzz pollination. The bumble bees want to eat the pollen: tomato flowers produce very little nectar.
Growing Tomatoes Tomatoes are often picked green (unripe), because they are firm and survive mechanical harvesting and shipping better. Much plant breeding work went into producing fruit that could be harvested mechanically. One result was the “square tomato”. They can be ripened with ethylene gas. Ethylene is a plant hormone that stimulates flower opening, fruit ripening, and leaf shedding in many plants. It has been used since ancient Egyptian times to stimulate fruit ripening, by burning incense or by gashing figs in a closed room. A modern use it to put unripe fruit in a closed paper bag with a banana, which concentrates the ethylene the banana produces and speeds ripening. It is produced by almost all plants, both as part of the natural fruiting cycle and in response to wounding or other stresses. Conversely, florists use ethylene inhibitors to extend the shelf life of cut flowers.
Flavr-Savr Tomatoes The Flavr-Savr tomato was the first genetically engineered food product allowed on the US market, starting in 1994. It was more resistant to spoiling and rotting, it had a longer shelf life, than normal tomatoes. This was accomplished by blocking the enzyme polygalacturonidase, which degrades the cell walls and makes fruit more susceptible to fungal infection (which is what rotting is). Didn’t catch on. A big problem was that the starting tomatoes were not from a high quality strain, so yield was less than half of what good commercial varieties produce, and many of the fruits were small. Also, the fruits were more delicate than regular tomatoes. Production ceased in 1997.
Apples Apple trees (Malus pumila) are native to central Asia. The capital city of Kazakhstan, Alma-Ata, means “father of the apple”. (The city is now named Almaty). Alexander the Great brought them back to Europe in 300 BC. Apples are members of the Rosaceae, the rose family. Many other fruits also come from three subdivisions of this family: The apple subfamily also includes pears and quinces. The fruits are called pomes. The plum subfamily includes plums, cherries, apricots, and peaches: “stone fruit”, also called drupes. The rose subfamily includes strawberry, raspberry, and blackberry. These are aggregate fruits: several ovaries fused together. Apples account for 60% of the temperate region’s fruit production. It is the world’s second largest fruit crop, after oranges.
Growing Apples Apples can be grown from seeds, that is, by sexual reproduction. However, apples are genetically diverse, and the process of meiosis ensures that every seed will be different from all others. This diversity is good for survival in nature, but it is bad for agriculture: there is no easy way to maintain specific varieties if the plants are grown from seed. Genetic uniformity is achieved by growing them vegetatively, by grafting cuttings onto the base of other trees. The base tree, called the rootstock, is from a strain that is disease-resistant and grows well in the region, but doesn’t produce high quality fruits. The scion (the grafted plant), produces good fruits of a specific variety. When new varieties are desired, the trees are grown from seed. Most new varieties appear spontaneously among the offspring of genetic crosses between different strains. Sometimes “bud sports” appear: mutations that occurred in a bid, producing a branch on a tree that it noticeably different from the rest of the tree.
Apple Flower and Fruit To produce fruits, apple flowers must be pollinated, usually by honeybees. The apple fruit consists of an ovary with 5 carpels fused together, surrounded by “accessory tissue”. The accessory tissue develops from the receptacle, the place where the flower is inserted into the plant stem. The swollen ovary containing the seeds is the core, and it is separated from the accessory tissue by a thin brown line. Most apples are picked by hand, either directly by the consumers or by low paid migrant workers. Mechanical harvesters are often used for cider apples: still not well developed.
A Few Apple Legends Adam and Eve, the first man and woman in the Bible. The Devil tempted Eve to eat the fruit of the Tree of Knowledge of Good and Evil, which God had forbidden. She then convinced Adam to eat it also. For this action, God tossed them out of the Garden of Eden and forced them and all their descendants to work for a living. But, this fruit may have actually been an apricot: it is not clear that apples grew anywhere near the Middle East when the Bible was written. William Tell, the Swiss hero and crossbow expert, refused to bow to the hat of the Austrian overlord (Gessler), which had been set on a pole in the town square. For this crime, he was forced to shoot an apple off his son’s head. When Gessler asked why he had taken out two crossbow bolts, Tell replied that if he had missed with the first one, the second arrow was meant for Gessler himself. This sparked a rebellion that led to Switzerland becoming free of the Austrian Empire in 1315. Isaac Newton supposedly “discovered” gravity, or at least had the insight that gravity attracted the Moon towards the Earth in the same way that it attracted the apple toward the Earth, when an apple fell on his head. And: New York City is “the Big Apple”, the Beatles’ record company Apple Corps, and the Apple computer company.
Johnny Appleseed Johnny Appleseed. = John Chapman (1774-1845). He spread apples to western Pennsylvania, Indiana and Ohio. He wore old ragged clothes, a pot on his head, and went barefoot most of the time. He was a vegetarian who was uncomfortable with romance, and he never settled down. Well-liked by all, a strong believer in the Swedenborg version of Christianity. At that time, this area was part of the Old Northwest Territory, land west of the Appalachian Mountains, only lightly settled by Europeans. It had been French territory, but was ceded to Britain in 1763. The British forbade European settlement west of the Appalachians. After the American Revolution, settlement began, despite armed resistance from the Native Americans. Resistance east of the Mississippi River ended in 1832, with the Blackhawk War in this part of Illinois. Abraham Lincoln participated. Johnny Appleseed had a business: he planted apple nurseries from seeds, then left a local resident in charge. After the trees grew, they were sold to the settlers. Apples were not well adapted to life in America, so using seeds instead of grafts aided in finding workable varieties.
Cider The apples planted by Johnny Appleseed were mostly used to make cider. We call this stuff hard cider today. Cider is made by grinding ripe apples, then pressing out the juice. The juice is allowed to ferment for up to 3 months. During this time period, cider was a common beverage, since water was generally contaminated. Fermentation stops when the alcohol content reaches about 10%: this kills the yeast. The alcohol in cider can be concentrated to make applejack. The pioneer method is freeze-distillation. The cider was simply left out in winter weather. Some of the water would freeze, as pure water ice, leaving the alcohol still liquid. The colder the weather, the stronger the cider. During Prohibition (1930’s), alcohol as illegal, and “cider” got re-defined as unfermented , unclarified apple juice . Sometimes called soft cider.
Citrus The citrus family (Rutaceae) contains many edible fruits: orange, grapefruit, tangerine, lemon, lime, and several other less well known species. Not really clear how many species there are: lots of hybrids, both ancient and modern. And, some "species" are clonally propagated and not sexually reproducing. The family is native to tropical southeast Asia. Most varieties are very sensitive to frost and can only be grown where it never freezes. Citrus flowers each have several carpels, and the fruits have a thick rind that surrounds a set of segments, each derived from a single carpel. The segments are filled with pulp.
Citrus History The citron was widely grown in the Mediterranean region in Greek and Roman times. Sour oranges, lemons, and limes were introduced by Arab traders in the Middle Ages. The sweet orange, today the world’s leading fruit crop, was brought to Europe by Portuguese traders in the 1500’s. Citrus came to the New World with the Spanish. Florida oranges are mostly grown for orange juice. Navel oranges came from Brazil, but all US navel oranges are probably descended from two trees planted in Riverside California in 1873.
Citrus Fruit Orange trees take 3 years to mature, and then bear fruit for about 20 years. Citrus fruits have a thick rind that contains oil glands. The glands secrete a fragrant essential oil, which attracts animals. The fruits have several fused carpels: each orange slice is derived from a single carpel. The fruits only ripen while on the tree, so they have to be picked when ripe, but not over-ripe. Oranges on the tree are a mottled yellow and green color. The orange color is due to carotene, which is masked by chlorophyll in the fruit. Ethylene gas can be used to speed up the degradation of the chlorophyll, leading to the orange color. Citrus fruits are high in vitamin C, which prevents scurvy.
Scurvy Scurvy is a disease caused by a vitamin C deficiency. Vitamin C is needed to help synthesize collagen, the main protein in our skin and connective tissue. A person with scurvy becomes weak and listless, spots form on the skin, and the mucus membranes bleed. In bad cases, old wounds open up and the teeth fall out. If not treated, it is lethal. Scurvy used to be very common on long sea voyages. Vitamin C is found in fruits, vegetables, and fresh meat, but all of these were lacking. Sailors ate salted meat and hard biscuits. Most animals, but not primates (or guinea pigs) can synthesize their own vitamin C. James Lind, a surgeon in the British navy, described how citrus fruits could prevent and cure scurvy in 1753. His ideas weren't consistently followed until the early 1900's. British sailors are called "limey" because they were forced to eat limes to prevent scurvy. Work with guinea pigs starting in 1907 led to the understanding that a specific nutrient was lacking, and eventually to the isolation of vitamin C and an understanding of how it works.
Orange Juice Most Florida oranges are converted into juice. Most fruit is hand picked. But mechanical harvesters are improving. One method is to shake the tree hard enough to knock all the fruit off. The ripe oranges are squeezed to extract the juice. Then, pulp and seeds are filtered out: most of this ends up as animal feed. The juice is then concentrated by evaporation, then frozen. It is now "frozen concentrated orange juice". It gets shipped to packaging plants around the country, often dairies, since the packaging process is the same as for milk. It gets reconstituted by adding water, then sold to the consumer. Some pulp is added back to produce the pulpy varieties favored by some consumers. Frozen concentrated orange juice is a commodity whose futures (bets on future costs) are traded publicly.
Brassica The Brassica genus is part of the mustard family. A wide variety of vegetable crops come from Brassica: they are called cole crops. The condiment mustard also comes from members of this genus. Members of Brassica oleracea include: cabbage, collard greens, kale, Brussels sprouts, kohlrabi, broccoli, and cauliflower. The different strains have been bred for different traits. Also, B. chinensis is bok-choi, B. campestris is turnip, and rutabaga is B. rapa. Also, B. napus is rapeseed or canola, B. nigra is black mustard, B. alba is white mustard, and B. juncea is brown mustard. The yellow color of prepared mustard (called American mustard in other countries) is due to tumeric added to the ground mustard seed. The hot taste of mustard is due to an enzyme reaction, which produces a volatile oil when the ground seeds are mixed with water.
Brassica Plants Brassica oleracea is native to the Atlantic coast of Europe, and was domesticated in ancient Greece. It is a cool weather crop. Mustard flowers are yellow or white, and they have 4 petals. The plants grow as a rosette of leaves that stays low to the ground. When it is mature, the plant "bolts". It shoots up a tall stem with the flowers on it. Most of the Brassica vegetable crops are harvested before bolting. The expression "gone to seed", meaning decreased in quality because of age and neglect, comes from this phenomenon. Although most Brassica vegetables are eaten fresh, cabbage can be converted to sauerkraut by shredding it and allowing it to ferment in salt water. Sauerkraut can be stored for a long time, and it retains vitamin C.
Brassica Breeding The different varieties come from breeding for different traits. Cabbage has lateral branches and meristems suppressed, so all growth goes into leaves produced by the terminal meristem. Brussels sprouts are similar to cabbage, except each lateral meristem develops into a little head. Kohlrabi is swollen stem bases. Broccoli heads are immature flower buds Cauliflower is a mass of stem tips, harvested before the flowers develop. The white color is due to a mutation that inhibits chlorophyll.
Triangle of U Brassica species easily hybridize, and there is a set of tetraploid species derived from hybridization of diploids followed by doubling the chromosomes. Chromosome numbers reflect the ancestral species. First noticed by Woo Jang-choon, a Korean working in Japan, in 1934. By the time his name had gone from Korean to Japanese to English, it came out Nagaharu U.
Jack-o'-Lantern Carving faces in turnips is (allegedly) an old tradition in the British Isles. Pumpkin carving is more recent (pumpkins are a New World crop). An Irish legend, with many variants explains the origin: Jack was a farmer who met up with the Devil one day. Jack managed to trap Satan in his wallet by putting a cross in there (the Devil lost his powers when faced with a cross). He let Old Scratch out only when he promised to never take Jack's soul. One day Jack died, and Heaven refused him: he hadn't been a very good person. And, due to his bargain, Hell also refused him. Jack was forced to wander for eternity in the darkness. But, the Devil, having a sense of humor, tossed him an ember from Hell, which never goes out. Jack hollowed out a turnip, his favorite vegetable, and put the ember in there to use as a lantern. He then wandered the Earth endlessly, and he became know as Jack of the Lantern, or Jack-o'-lantern.
Banana Genus Musa, several species. All edible bananas are lumped together as Musa x paradisiaca, which reflects their hybrid origin. Two forms are popular: the sweet banana we eat as a fruit, and the starchy plantain, which is cooked and eaten as a vegetable in many tropical countries. In Asia, they are also used for beer making, and in general are used about like we use potatoes. Also, fiber for cloth and paper can be extracted. Native to Southeast Asia and northern Australia. The wild banana was very important in pre-agricultural days. Probably first domesticated in New Guinea Spread to India by 600 BC, and throughout the Pacific Ocean region by the Polynesians. Arab traders brought it to Africa about 2000 years ago. It flourished and spread throughout the Old World tropics. Brought to the New World by the Portuguese in the 1500’s. Did well here too.
Bananas as Plants The banana is a monocot, and the trunk of the banana tree is really tightly packed leaf bases arising from an underground corm. The plant takes about a year to mature, starting from a cutting. It then flowers and sets fruit. The plant then dies, but the corm send out new stems (called suckers). Fruits are picked green (unripe). Ripening is induced are they have been shipped to market, by treating them with ethylene gas. Most varieties are sterile triploids, which are propagated vegetatively. They are seedless for this reason. Also leaves them vulnerable to pathogens: bananas are genetically identical, so a pathogen that kills one will probably be able to kill all of them. The banana industry is periodically devastated by such diseases, and much breeding work goes into developing resistant varieties.
Seedless Fruit Banana fruits develop without fertilization. This is called parthenocarpy, and it is a common way of getting seedless fruit. It is due to a spontaneous genetic mutation, and it is found naturally in many plants. When a plant is moved from its ancestral home to another part of the world, the pollinating insect (or bird, etc.) often doesn’t came along or can’t survive. A variation on parthenocarpy: some fruits need fertilization to develop, even though the embryos abort. Thus the seeds are tiny or non-existent. In some species, spraying with plant hormones like auxin can induce parthenocarpy. This is commonly done with garden tomatoes. This can also be done with genetic engineering. Triploids are naturally sterile and seedless. Triploids can be propagated vegetatively, or triploid seeds can be produced by crossing a diploid with a tetraploid.
Banana Republics Bananas rot quickly after harvest. Before steam ships, they were almost unknown in temperate climates. Around 1900, refrigerated steam ships were able to bring them to market in America and Europe. This led to a vast increase in their popularity. At one point, bananas were cheaper than local-grown apples! The United Fruit Company owned much of the land and infrastructure in several Central American countries, including Nicaragua, Honduras, Guatemala, Panama, and El Salvador. The people who had formerly farmed the land were then hired at extremely low wages to work the plantations. Several violent coups were engineered by United Fruit to remove popular governments that wanted to interfere. Vastly unequal distribution of wealth and political problems remain as a legacy in Central America to the present time.
Carrots Daucus carota. Domesticated form of Queen Anne's Lace, a common roadside flower in late summer. Umbel-shaped flower. Contains carotene, the orange pigment which the body converts to vitamin A (retinol), the visual pigment. The idea that eating a lot of carrots will improve your night vision started in England in World War 2, when British gunners were able to accurately shoot down German airplanes in the dark of night. This was actually because the British had invented radar, but they didn't want the Germans to know that, so the British government propaganda ministry started the rumor about carrots. biennial: grow as a low rosette of leaves one year, store food in underground taproot (which we eat), then send up a flower stalk the next year using that food. We harvest it after the first growing season. Diploid, grown from seed. Commercial seed is inbred enough to give uniform growth, but not so inbred as to produce inbreeding depression.
Carrots Native to Afghanistan (it's the center of diversity). And other temperate parts of western Asia and eastern Europe. In the wild, carrot roots are branched and woody: we have selected for a single unbranched taproot. When first domesticated, carrots were purple. Caused by a pigment called anthocyanin, which is used in many flowers for red, pink, and purple shades. It's water soluble, producing purple-brown stews Spontaneous mutants removed this pigment: same taste, but no ugly color in the stew.
Other Carrot Family Crops Carrots are members of the Apiaceae (also called Umbelliferaceae) family. Aromatic plants with hollow stems, feathery leaves, and flowers like umbrellas. The flowers attract parasitic wasps, which kill garden insects. This makes carrots good companions for other garden plants. We also eat parsnips, which look a lot like white carrots. And celery is also a member of this family. Many aromatic herbs: parsley, dill, coriander, cilantro, cumin, fennel, caraway (seeds in rye bread), anise (licorice flavor). Coriander is the seeds and cilantro the leaves of the same plant. Some are quite poisonous. For example, hemlock, which Socrates was forced to drink for his execution for corrupting the morals of the young. Hemlock grows wild here in Illinois Silphium, a giant member of this family, was used for birth control in ancient Roman Empire. It is now extinct. Grew only in a small region of the Mediterranean coast in Libya, and it was over-used.
Onions Allium cepa. Onions are in the Lily family, which is a monocot. Onion is really a biennial or perennial: the bulb grows in one year, then it sends up a flower stalk in the next year. We harvest them after the first season. We eat the bulb: underground stem base surrounded by fleshy leaves In former times it was used as medicine for a large number of ailments. Smell due to release of smelly sulfur compound Tears when cutting come from release of sulfuric acid and related compounds. Can be grown from seed or from seed sets, which are small onions grown from seed: using a seed set gives them a head start so they get bigger during the growing season.
Onions Wild onions are edible: it was probably harvested from the wild long before it was cultivated. Cultivated from early times in both Egypt and China by 3000 BC. It stores well. Wild relatives in Central Asia, so that's probably where it was first domesticated, but no direct proof of this. We tend to use onion as a food flavoring, but it can also be eaten as a vegetable unattributed odd "fact": the people who built in Pyramids in Egypt may have lived on radishes and onions. Wikipedia links to a food/garden site that just says it out of the blue. Onion (as Allium) is a garden flower: blue puffball heads. It's a perennial. Other relatives: garlic, leek, shallot, chives. Garlic usage has greatly increased in the US in recent years: people like spicier food.
Squashes and Melons Both are members of the Curcurbitaceae, the cucumber family. Squashes domesticated in New World, melons in Old World: Africa and South East Asia independently. Very early domestication. All are creeping vines with separate male and female flowers on the same plant. We eat the fruits, which have multiple seeds surrounded by a fleshy fruit that has a hard rind. Originally grown for the seeds: wild relatives can be eaten but the flesh is bitter. Seeds high in sulfur-containing amino acids. Pumpkin seeds are still widely eaten. Hard rind makes them easy to store, and soft flesh works well as a water source in the desert.
Squash Squash: four cultivated species in the genus Curcurbita, with lots of variation in form within each species, and overlapping between species. E.g., "winter squash" and "pumpkin" can be any one of the four. Types: pumpkins, zucchini, butternut, turban, acorn, summer, plus others. Squash was gown along with maize and beans in ancient Mexico. The vine provides a ground cover that suppresses weeds, the beans fertilize the soil by fixing nitrogen, and the maize provides a living pole for the beans to grow on. This is called the “three sisters” method. Giant pumpkins are Curcurbita maxima. Current record (2010): 1810.5 pounds. It’s been going up by 50 pounds a year or so.
Melons Watermelon are from west Africa. Eaten in ancient Egypt by 2000 BC. King Tutankhamen's tomb contained many watermelon seeds. Grown in China by 1000 AD. Cantaloupe and honeydew melons are from central Asia. Also cucumbers: same species. Cucumbers can be turned into pickles by soaking them in salt water (brine) at low pH (acid). Sometimes vinegar is added, along with spices such as dill and garlic. A bacterial fermentation process turns them sour. Originally used for food preservation, now mostly for flavor. Other vegetables can be pickled. Playwright Neil Simon once said, “Words with a k in it are funny. Alka-Seltzer is funny. Chicken is funny. Pickle is funny....” Loofah is a species of curcurbit whose fruit is allowed to partially rot, leaving a network of fibrous tissue. This is used for scrubbing your body: the loofah sponge. The fruit can also be eaten as a vegetable before it matures.
Calabash The calabash, or bottle gourd, is another curcurbit of note. It was one of the first domesticated plants. It is grown for use as a container, not for food. When dried out, the woody rind in strong and waterproof. Also used as a body for musical instruments,: stringed, rattles and drums and often highly decorated. It also has been used for smoking pipe bowls: Sherlock Holmes (a fictional character) smoked a calabash pipe.
Calabash Origins The calabash originated in the dry warm areas of southern Africa, where there a wild relatives. The wild species have thin rinds: the cultivated varieties have clearly been selected for thick waterproof rinds. However, the calabash reached Asia very early: it has been found at archeological sites that are 8000 years old. Today Asian and African varieties are relatively distinct. The calabash was also grown in the New World 8000 years ago, long before Columbus. This leads to. another ancient contact story: how did it get to the Americas? The main theory for the past 150 years: it rafted across the Atlantic Ocean from Africa in a mass of vegetation without human assistance. The rind is quite waterproof and the seeds are capable of germinating after a long dormancy period. Alternative: a boatload of African fishermen blown off course and landing in South America. Much less likely: by boat across the Pacific Ocean. Polynesia was settled much later: between 3000 and 1000 years ago.
More Calabash Origins Recent genetic and archeological study shows that the pre-Columbian calabash in America came from Asia. (D.L. Erickson et al., 2005, Proc. Nat. Acad. Sci USA 102:18315-18320) This suggests it came over the Bering Land Bridge around 12,000 years ago with the original inhabitants of the New World, the Paleoindians. Sea level was much lower at that time, due to the Ice Age glaciers locking up much water. They were hunter-gatherers: settled agriculture hadn’t been invented yet. They also brought the dog to the New World. Dates from carbon-14 decay. It gets into plants from carbon dioxide in the atmosphere. When the plant dies, no new C-14 is added, and it slowly decays into nitrogen. So, the amount of C-14 left is proportional to how long ago the plant died. Calibrated by counting tree rings. In some places, tree ring chronologies go back 10,000 years.
Genetic Evidence The scientists involved here wanted to compare DNA from New World archeological specimens to plants grown today in Africa and Asia. They collected calabashes from traditional farmers in both Africa and Asia, to avoid getting seeds form modern cultivars. Also needed very careful treatment of archeological material to avoid contaminating ancient DNA with modern DNA. Looking for differences in the DNA that would reliably distinguish between Asian and African varieties. There are a few regions in the genome that are easy to analyze and known to be quite variable. Mostly, the Asian and African varieties proved to be very similar in their DNA. Found three good differences in the chloroplast DNA. All modern Asian varieties had one allele and all modern African varieties had the other allele. Results: of the 12 archeological samples, only 10 produced any data. Of these, the nine that had pre-Columbian dates all had the Asian DNA markers. The one with a post-Columbian date had the African markers: Columbus brought the African variety to the New World, and it has mostly replaced the Asian variety. So, there is strong evidence that the pre-Columbian calabash came from Asia. How it got there is not proven: the Bering Land Bridge theory fits well with other knowledge of how the New World was settled.
Tropical Fruits Pineapple, date, figs, coconut, avocado, pomegranate, mango, papaya. Plus lots of others that are very tasty but don't ship well, so are only eaten locally. Not to mention nuts, which we haven't even touched on. The mind boggles…
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