The Variation of Animals and Plants Under Domestication Informative Summary

Overview:

Darwin’s Variation of Animals and Plants under Domestication expands on his groundbreaking work in On the Origin of Species by focusing on the principles of artificial selection. Darwin meticulously investigates the changes animals and plants undergo under human influence, using a wealth of empirical observations and historical accounts to demonstrate the plasticity of life forms.

The first volume delves into a species-by-species examination of domesticated animals, examining the variations within each species and exploring the probable origins of these variations. Darwin uses dogs as a prime example, presenting a strong argument for the multiple origins of domesticated dogs, suggesting that various wild canines were independently domesticated and later crossed. The book explores the variability of each species in terms of its skull, teeth, limbs, coloration, and temperament, highlighting the enormous influence of artificial selection in shaping these characteristics.

Key Findings:

  • Multiple Origins of Domesticated Species: Darwin argues that many domesticated species, including dogs, pigs, and cattle, likely originated from multiple wild species, which were then crossed and further modified by artificial selection.
  • Power of Selection: Darwin emphasizes the immense power of both methodical and unconscious selection in shaping domesticated animals and plants. He showcases how humans, through careful breeding practices and preferences, can significantly alter a species’ traits over time.
  • Reversion: Darwin identifies reversion (or atavism) as a crucial mechanism in the formation of new varieties. He demonstrates how offspring can exhibit traits from their grandparents or even more distant ancestors, a phenomenon particularly evident in the appearance of blue plumage with characteristic markings in crossed pigeons.
  • Effects of Use and Disuse: Darwin posits that the increased use of organs, like muscles, strengthens them, while disuse weakens them. He explores the evidence of this phenomenon in domesticated animals, particularly those with reduced organs of flight due to their confinement.

Learning:

  • Artificial Selection: The reader will gain a deep understanding of the process of artificial selection, how humans have systematically modified animal and plant varieties to suit their needs and preferences.
  • Variability and Inheritance: The text sheds light on the principles of variability and inheritance, explaining the mechanisms through which traits are passed down through generations and how changes in the environment can influence these traits.
  • Reversion (Atavism): The reader will learn about the phenomenon of reversion, the tendency for organisms to exhibit traits from their ancestors, even if those traits have not been present in recent generations. This concept provides a crucial link between artificial selection and the evolutionary process.
  • Effects of Use and Disuse: Darwin’s analysis of use and disuse, the principle that increased use strengthens organs, while disuse weakens them, provides insight into the selective pressures that can drive evolutionary change.

Historical Context:

Darwin’s Variation of Animals and Plants under Domestication was published in 1868, a time of intense scientific and social debate surrounding the theory of evolution. This book serves as a direct response to critics who questioned the plausibility of natural selection. By showing how humans have been able to shape life forms through selective breeding, Darwin strengthened his argument for the efficacy of natural selection in driving the evolution of species over vast periods.

Facts:

  • Dogs: Domestic dogs likely originated from multiple wild canine species, including wolves and jackals. The habit of barking is not present in any wild canine but is easily acquired and lost by dogs under domestication.
  • Horses: The wild horse (Equus caballus) likely had stripes along its back, legs, and shoulders. Dun-coloured horses are most frequently striped, suggesting reversion to an ancestral trait.
  • Pigs: Pigs belong to two distinct types, Sus scrofa and Sus indicus. Pigs of the Sus indicus type are best known under the form of the Chinese breed. Domestic pigs have been crossed with wild boars throughout their range.
  • Cattle: European cattle are likely descended from two wild species, Bos primigenius and Bos longifrons. Zebus, or humped cattle, are a distinct species from European cattle.
  • Sheep: Domestic sheep are probably derived from multiple wild species and have undergone remarkable variation under domestication. Fat-tailed sheep have a tail that can be as long as twenty vertebrae.
  • Goats: Domestic goats likely originated from Capra ægagrus, possibly crossed with the Indian Capra falconeri.
  • Rabbits: All domestic rabbits are descended from the European wild rabbit (Oryctolagus cuniculus). Wild rabbits can be domesticated but this process is often difficult.
  • Pigeons: All domestic pigeons are descended from the rock pigeon, Columba livia, or its closely-related sub-species.
  • Fowls: Most domestic fowls are believed to be descendants of Gallus bankiva, which is closely related to the Game fowl. Wild cocks sometimes mate with domestic hens.
  • Ducks: Domestic ducks are likely descended from the mallard (Anas boschas). Ducks are easier to domesticate than most birds.
  • Geese: The domestic goose is likely descended from the wild greylag goose (Anser ferus).
  • Peacocks: The black-shouldered peacock is a strongly marked variety, or “sport,” that tends to reappear within flocks of common peafowl.
  • Turkeys: The domestic turkey is derived from a Mexican wild species.
  • Guinea-fowl: The domestic guinea fowl is likely descended from Numida ptilorhynca, a native of eastern Africa.
  • Canary-birds: The canary bird has been crossed with other species of finch, but no new breeds have been created from these crosses.
  • Goldfish: Goldfish have been domesticated in China for centuries, and have undergone remarkable variations in color, size, and structure.
  • Bees: There is no evidence of distinct breeds of hive bees, with the exception of the Ligurian race, which is likely a distinct species, not a product of domestication.
  • Silk-moths: Several species of silkworms are domesticated, but most European silkworms are believed to be of the same species (Bombyx mori).
  • Plants: Most cultivated plants are still recognizable as varieties of their wild counterparts.
  • Wheat: There is much debate about the number of wild wheat species, but it is generally believed that all varieties are descended from a single or a few species. There is a strong tendency to inheritance in wheat varieties, which can be enhanced by selecting for traits from single ears.
  • Maize: All cultivated maize is believed to be of the same species (Zea mays) and is of American origin. Maize has undergone remarkable variation under domestication, including significant differences in height, ear shape, seed color, and time of maturity.
  • Cabbage: The varieties of cabbage are highly variable in their leaves and stems but show little variation in their flowers, seed-pods, and seeds.
  • Peas: Garden peas are likely descended from a single species, though there is debate about the distinction between them and field peas (Pisum arvense). Pea varieties show considerable variation in their pods and seeds, which are the selected parts.
  • Potatoes: The cultivated potato is very similar to its wild progenitor. Potato varieties show the greatest diversity in their tubers.
  • Grapes: All cultivated grapes are believed to be descendants of Vitis vinifera, which is found wild in western Asia. Grapes are highly variable, and new varieties are continually being developed.
  • Mulberries: The white mulberry (Morus alba) has varied in the texture and quality of its leaves, which are used to feed silkworms.
  • Oranges: There is much debate about the origins of cultivated oranges, lemons, and citrons. They are believed to be separate species by some, but others consider them to be varieties of Citrus medica.

Statistics:

  • Dogs: A single hybrid wolf-dog can produce offspring that are even wilder than wolves.
  • Horses: About a third of Norwegian ponies have striped legs.
  • Pigs: The Yorkshire breed of pig has undergone significant changes in head shape in less than 30 years. The presence of just 1/32 of Sus indicus blood can noticeably alter the skull of Sus scrofa.
  • Cattle: The horns of Bechuana cattle can be as long as 8 ft 8 1/4 in. (measured in a straight line) and 13 ft 5 in. (measured along their curvature).
  • Sheep: The fat-tailed sheep of the plains of India can have a tail that includes up to 20 vertebrae.
  • Rabbits: The ears of a lop-eared rabbit can be as long as 23 1/8 inches (measured from tip to tip).
  • Pigeons: Fantail pigeons can have as many as 42 tail feathers.
  • Fowls: Cochin fowls can weigh up to 17 pounds. The comb of a Red-cap fowl can be more than 3 inches in breadth and 4 inches in length. The skull of a black-boned Silk fowl is twice as large as that of Gallus bankiva.
  • Ducks: The eggs of a black Labrador duck are sometimes tinted black. A Hook-billed duck can lay up to 80-100 eggs per year. The femur and metatarsus of a Penguin duck are elongated.
  • Geese: The scapular feathers of a Sebastopol goose can be curled and spirally twisted.
  • Peacocks: A black-shouldered peacock can weigh up to 2 pounds 2 1/2 ounces.
  • Canary-birds: A Belgian canary can be up to 8 inches in length, while the wild canary is only 5 and 1/4 inches long.
  • Goldfish: There are over 89 varieties of goldfish.
  • Silk-moths: There are at least 6 species of silkworms domesticated throughout the world.
  • Wheat: The grains of wheat from the Swiss lake-dwellings were only 4-7 mm. long, whereas modern grains can be 7-8 mm. long.
  • Maize: The ear of a maize variety can be four times as long as that of a dwarf kind.
  • Cabbages: The stem of an arborescent cabbage can reach 16 feet in height.
  • Peas: The tallest pea variety can grow up to 8 feet, while the shortest variety is only 6-12 inches tall.
  • Potatoes: The tubers of some Peruvian potatoes can be 6 inches in length and only as thick as a man’s finger.
  • Oranges: The average weight of a sweet orange can be more than 2000 times the weight of the smallest variety.
  • Melons: The weight of a melon can range from the size of a small plum to 66 pounds.
  • Trees: The leaves of some oak-leaved laburnums can be up to 18 inches in length and 6 inches in breadth.
  • Roses: Over 2562 varieties of roses are known to have been cultivated in France.
  • Pansy: Over 400 named varieties of pansies were on sale in 1835.
  • Dahlias: Over 300 varieties of dahlias could be purchased in 1841.
  • Hyacinths: Nearly 2000 varieties of hyacinths were known in 1768.

Terms:

  • Artificial Selection: The intentional process of selecting and breeding individuals with desired traits to create new varieties.
  • Unconscious Selection: The unintentional preservation of certain traits through the repeated selection of individuals with those traits, without a specific goal of altering the breed.
  • Natural Selection: The process by which organisms better adapted to their environment survive and reproduce more successfully, leading to the gradual evolution of species.
  • Reversion (Atavism): The reappearance of traits from ancestors in an individual, often due to the mixing of genes from different varieties or species.
  • Prepotency of Transmission: The tendency for one parent to more strongly influence the traits of its offspring than the other parent.
  • Sexual Selection: A form of natural selection in which individuals with certain traits are more successful at attracting mates, leading to the evolution of traits like bright coloration, elaborate displays, or weapons.
  • Bud-Variation: The sudden appearance of a new trait in a plant that is not inherited through seed, but through a modification of a bud.
  • Graft-Hybrids: Hybrids produced through the union of cellular tissue from two distinct varieties or species, without the intervention of sexual organs.
  • Contabescence: A condition in which the anthers of a plant become shrivelled, brown, and tough, losing their ability to produce viable pollen.
  • Peloria: The abnormal development of a flower with symmetrical features, which often results from an arrest of development or reversion to a primordial state.

Examples:

  • Dogs: The Newfoundland dog was imported into England from Newfoundland and has been significantly modified since its introduction.
  • Horses: Lord Morton’s mare, a chestnut with Arabian blood, produced foals that resembled a quagga (an extinct relative of the zebra) even though the foals were sired by a black Arabian horse.
  • Pigs: The Japanese pig is an example of a breed that has undergone remarkable modification under domestication.
  • Cattle: The niata cattle of South America have short, broad foreheads, protruding lower jaws, and a distinctive upturned nose.
  • Sheep: The fat-tailed sheep of the plains of India have an extraordinarily large mass of fat on their tails.
  • Goats: The goats of Syria and Nubia have bilobed mammæ, different from the common goat.
  • Rabbits: The Himalayan rabbit, with its white body and dark ears, nose, feet, and tail, is an example of a new breed created through intercrossing.
  • Pigeons: The short-faced tumbler pigeon, with its tiny beak and globular head, is one of the most striking examples of artificial selection.
  • Fowls: The Cochin fowl is a large breed with fluffy plumage, short wings, and a distinctive crow.
  • Ducks: The Penguin duck walks with an extremely erect body and has elongated femur and metatarsus bones.
  • Geese: The Sebastopol goose is a breed with curled and spirally twisted scapular feathers.
  • Peacocks: The black-shouldered peacock is a rare variety of the common peacock.
  • Turkeys: The Copper-coloured or Cambridge turkey is a breed that breeds true.
  • Canary-birds: The Belgian canary has a much elongated body, unlike the wild canary.
  • Goldfish: The goldfish has many varieties with abnormal structures, such as triple tail fins.
  • Wheat: Major Hallett’s Pedigree Wheat is a variety that was created through the careful selection of plants from the grains of the same ear.
  • Maize: The “sweet corn” variety of maize has curiously wrinkled seeds.
  • Cabbages: The Kohlrabi or choux-raves are a type of cabbage with enlarged, turnip-like stems.
  • Peas: The Sugar peas have thin pods that are eaten whole.
  • Potatoes: The gurken-kartoffeln variety of potato grows its tubers in a pyramid shape with the apex downwards.
  • Grapes: The Pedro-Ximenes grape is characterized by the yellowing of its leaves when the fruit is nearly ripe.
  • Mulberries: The roso variety of mulberry is valued for its hardy leaves, which are easily collected.
  • Oranges: The myrtle-leaved orange is a distinct variety of the common orange.
  • Roses: The double moss-rose was imported into England from Italy in 1735.
  • Pansy: The pansy has been dramatically improved by selection, with its flowers now being much larger, flatter, and more symmetrical than those of the wild pansy.
  • Dahlias: The dahlia has been dramatically modified since its introduction in the early 19th century, with the flowers now being available in a variety of colors and shapes.
  • Hyacinths: The hyacinth has been cultivated for centuries, and its flowers have been greatly modified in shape, size, and color.

Conclusion:

Charles Darwin’s Variation of Animals and Plants under Domestication presents a compelling case for the power of selection in shaping the evolution of life. Darwin argues that through both conscious and unconscious selection, humans have been able to profoundly modify the characteristics of animals and plants, highlighting the inherent plasticity of life forms. This book provides a foundation for understanding the broader processes of natural selection and evolution by demonstrating how human intervention can drive change in the biological world.

The book emphasizes the key role of variability in evolution, showing how even slight variations in traits can be amplified through selection to produce dramatic changes. Darwin also explores the complexity of inheritance, demonstrating that traits can be inherited from ancestors, even if they are not present in recent generations. Additionally, he highlights the significant influence of the environment on the development and propagation of organisms, exploring the effects of use and disuse, changed conditions of life, and the role of climate and nutrition.

While the book does not provide a definitive explanation for the causes of variability, it reveals the immense power of selection and emphasizes the importance of understanding the intricate interplay between the organism and its environment in driving biological change.

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