EVOLUTION THAT SHPES LAND RACES

Evolution that shapes landraces

Herbert Spencer defined the evolution Herbert Spencer defined the evolution as "unrolling or unfolding of events". as "unrolling or unfolding of events". Charles Darwin described evolution as Charles Darwin described evolution as descent with modification. In other words, descent with modification. In other words, evolution may be described as derivation of evolution may be described as derivation of new special plants and animals from those new special plants and animals from those existed in the past.existed in the past.

The theory of special creation states that every The theory of special creation states that every organism on the face of earth is a separate, organism on the face of earth is a separate, distinct, fixed entity is not accepted since distinct, fixed entity is not accepted since evidence is available to show that organisms evidence is available to show that organisms were in evolutionary progress in the past and were in evolutionary progress in the past and are continuing to change at present. The theory are continuing to change at present. The theory of evolution rejects the idea of fixity of species of evolution rejects the idea of fixity of species and advocats the universal operation of an and advocats the universal operation of an orderly process of change.orderly process of change.

Domestication This is closely related to the former This is closely related to the former

evidences. Cultivation of plants brings many evidences. Cultivation of plants brings many changes in an individual. The plants growing in changes in an individual. The plants growing in wild state are so much altered that they bear no wild state are so much altered that they bear no resemblance to it. Thus Brussels sprouts, resemblance to it. Thus Brussels sprouts, cauliflower knol‑khol etc are all varieties derived cauliflower knol‑khol etc are all varieties derived from a single wild species Brassica oleracea of from a single wild species Brassica oleracea of Europe. Similarly domestication has brought Europe. Similarly domestication has brought several results of various colours having numerous several results of various colours having numerous petals.petals.

It has been seen that many allied species of plants in their It has been seen that many allied species of plants in their wild state remain distributed only to a particular area. wild state remain distributed only to a particular area. This indicates that they have evolved from a common This indicates that they have evolved from a common ancestor in that region and could not migrate owing to ancestor in that region and could not migrate owing to some geographical barriers such as high mountains, seas, some geographical barriers such as high mountains, seas, and deserts. For the confirment of a species in at a and deserts. For the confirment of a species in at a particular place many examples can be given, travellers particular place many examples can be given, travellers tree in Madagascar, cacti in the dry region of tropical tree in Madagascar, cacti in the dry region of tropical America, Eucalyptus in Australia etc. They often occur America, Eucalyptus in Australia etc. They often occur with allied species close together, showing thereby that all with allied species close together, showing thereby that all the allied species have evolved from the same ancestral the allied species have evolved from the same ancestral species.species.

Theories of EvolutionTheories of Evolution 1. Lamarckism (Theory of Inheritance of Acquired 1. Lamarckism (Theory of Inheritance of Acquired

Characters)Characters) Jean Baptiste Lamarck (1744‑1829) proposed the Jean Baptiste Lamarck (1744‑1829) proposed the

theory of inheritance of acquired characters which is theory of inheritance of acquired characters which is popularly known as Lamarckism. He is a French Biologist. popularly known as Lamarckism. He is a French Biologist. He began his career as a botanist but later became a zoologist. He began his career as a botanist but later became a zoologist. He was holding a position of Zoologist in Jardin des plantes.He was holding a position of Zoologist in Jardin des plantes.

Although Lamaracks views on evolutionary mechanism Although Lamaracks views on evolutionary mechanism is out moded now, he still occupies a very important place in is out moded now, he still occupies a very important place in the history of evolutionary thought. he was the first person to the history of evolutionary thought. he was the first person to conclude that evolution is a general fact covering all forms of conclude that evolution is a general fact covering all forms of life.life.

Lamarck

Lamarck published his views in 1809 in his Lamarck published his views in 1809 in his book on “Philosophie Zoologique” (The book on “Philosophie Zoologique” (The philosophy of Zoology). (Other books are philosophy of Zoology). (Other books are Researches Surle Organization des corps Researches Surle Organization des corps vivant (1802), Historic Naturelle des vivant (1802), Historic Naturelle des Animaux sans Vertebres (1815 ‑22)Animaux sans Vertebres (1815 ‑22)

He proposed his theory at a time when He proposed his theory at a time when the world was not ready to listen to him on the world was not ready to listen to him on the views of evolution. He put forth his the views of evolution. He put forth his ideas under four laws.ideas under four laws.

Nature tends to increase the size of the Nature tends to increase the size of the organism and its component parts.organism and its component parts.

The production of a new organ is the new The production of a new organ is the new need felt by the organism.need felt by the organism.

Constant use of an organism makes better Constant use of an organism makes better development while disuse causes its development while disuse causes its degeneration.degeneration.

Acquired characters during the lifetime of Acquired characters during the lifetime of an organism will be inherited to its an organism will be inherited to its offspring.offspring.

Effect of Environment Effect of Environment It is common knowledge that environment may It is common knowledge that environment may

influence the form of organism. Thus a plant grown in influence the form of organism. Thus a plant grown in fertile soil will have a luxuriant form while the same fertile soil will have a luxuriant form while the same plant in a barren tract will be sickly and stunted. In the plant in a barren tract will be sickly and stunted. In the case of animals the effect of environment may also be case of animals the effect of environment may also be indirect as the habits of animals may change in a new indirect as the habits of animals may change in a new environment and a change of habits, according to environment and a change of habits, according to Lamarck, causes a change of from. Lamarck assumed Lamarck, causes a change of from. Lamarck assumed that such changes of form caused by the direct or indirect that such changes of form caused by the direct or indirect effect of environment re inherited and are of cumulative effect of environment re inherited and are of cumulative nature. Thus in course of generations new species may nature. Thus in course of generations new species may be formed.be formed.

Conscious EffortConscious Effort The production of a new organ or part in the The production of a new organ or part in the

animal body results from a new need or want animal body results from a new need or want which continues to make itself felt and thus want which continues to make itself felt and thus want is a result of the production of a new movement is a result of the production of a new movement and it is maintained. There is inner urge in the and it is maintained. There is inner urge in the animals with which the effect of the environment animals with which the effect of the environment produces a new character according to its mode produces a new character according to its mode of life.He emphasis was not only on the effort of of life.He emphasis was not only on the effort of the organism but on the unconscious effect of the the organism but on the unconscious effect of the environment on the organism.environment on the organism.

Use and DisuseUse and Disuse The degree of development of organs and The degree of development of organs and

their force of action are always proportionate to their force of action are always proportionate to the use made of these organs.In simple words it the use made of these organs.In simple words it can be said that only those organs which are put can be said that only those organs which are put into constant use will develop better and those into constant use will develop better and those which are put into dis use will gradually which are put into dis use will gradually disappear.This is known as the law of use and disappear.This is known as the law of use and disuse or kinetogenesis.disuse or kinetogenesis.

In support of the above views Lamarck put In support of the above views Lamarck put forward the classical example of giraffe. The forward the classical example of giraffe. The ancestors of the giraffe were animals like horses ancestors of the giraffe were animals like horses with normal limbs and neck once there were no with normal limbs and neck once there were no grasses in the earth, and they have to eat only grasses in the earth, and they have to eat only leaves on the trees. For that they have to stretch leaves on the trees. For that they have to stretch their neck to eat the leaves of higher and higher their neck to eat the leaves of higher and higher branches. Thus abnormal lengthening of the neck branches. Thus abnormal lengthening of the neck resulted. The forelimbs of also lengthened like resulted. The forelimbs of also lengthened like that. This character is transmitted to the next that. This character is transmitted to the next generation.generation.

Another typical example was that of the Another typical example was that of the water bird with webbed feet. When a water bird with webbed feet. When a land bird was taken to water, it would land bird was taken to water, it would have to spread its toes while swimming have to spread its toes while swimming and the skin between the toes would have and the skin between the toes would have broadened and grown more and more in broadened and grown more and more in the successive generations and the the successive generations and the accumulated growth of the skin between accumulated growth of the skin between the toes would have resulted in the the toes would have resulted in the appearance of a web.appearance of a web.

The animals living in the cave generally show The animals living in the cave generally show degenerate features like the reduction and the degenerate features like the reduction and the elimination of the eye and the gradual disappearance elimination of the eye and the gradual disappearance of the pigment of the skin and the presence of of the pigment of the skin and the presence of sensory structures like antenna etc. These are sensory structures like antenna etc. These are supposed to be instances of acquired characters supposed to be instances of acquired characters being inherited gradually. Another example can be being inherited gradually. Another example can be quoted of horse. The ancestors of modern horse left quoted of horse. The ancestors of modern horse left the soft ground of forests and took to life on dry the soft ground of forests and took to life on dry plains. This change in habit was accompanied by plains. This change in habit was accompanied by change in length and structure of legs, which were change in length and structure of legs, which were suited for fast running over hard ground.suited for fast running over hard ground.

Lamarck offered certain example of these organs, which were not Lamarck offered certain example of these organs, which were not used and became reduced or atrophied. The wings of ratite birds used and became reduced or atrophied. The wings of ratite birds are said to be an example.The formerly flying birds have lost their are said to be an example.The formerly flying birds have lost their power of flight due to disuse of the wings as there was no necessity power of flight due to disuse of the wings as there was no necessity for these birds to take into air and thus they have become flightless for these birds to take into air and thus they have become flightless birds with reduced wings.Another example is that of the absence of birds with reduced wings.Another example is that of the absence of limbs in snakes.They have disappeared due to disuse. Since snakes limbs in snakes.They have disappeared due to disuse. Since snakes crawl and burrow the limbs present would have been a hindrance crawl and burrow the limbs present would have been a hindrance in that mode of progression. Hence, these became gradually in that mode of progression. Hence, these became gradually reduced and after many generations they were completely reduced and after many generations they were completely atrophied.Thus numerous examples can be cited. In all the above atrophied.Thus numerous examples can be cited. In all the above examples it can be seen that those organs which are constantly put examples it can be seen that those organs which are constantly put into use are better developed and those which are not used will into use are better developed and those which are not used will generally atrophy. Thus his theory of use and disuse is proved.generally atrophy. Thus his theory of use and disuse is proved.

Inheritance of Acquired CharactersInheritance of Acquired Characters All that have been acquired imprinted or All that have been acquired imprinted or

changed in the organization of the individuals during changed in the organization of the individuals during the course of its life due to direct or indirect the course of its life due to direct or indirect environmental effect is preserved by generations and environmental effect is preserved by generations and transmitted to the offspring.This law is known as the transmitted to the offspring.This law is known as the inheritance of acquired characters. All serious inheritance of acquired characters. All serious experiments performed to test this postulate gave experiments performed to test this postulate gave negative results except Mc Dougalls experiments on negative results except Mc Dougalls experiments on rats.Weisman was perhaps the first person who for the rats.Weisman was perhaps the first person who for the first time made a definite distinction between heritable first time made a definite distinction between heritable changes and those which cannot be inherited.changes and those which cannot be inherited.

Charles Darwin

Darwin’s Theory of Evolution

Evolution, or change over time, is the , or change over time, is the process by which modern organisms have process by which modern organisms have descended from ancient organisms. descended from ancient organisms.

A scientific A scientific theory is a well-supported is a well-supported testable explanation of phenomena that testable explanation of phenomena that have occurred in the natural world.have occurred in the natural world.

Voyage of the Beagle

Voyage of Beagle Dates: Dates: February 12th, 1831February 12th, 1831 Captain:Captain: Charles Darwin Charles Darwin ShipShip: H.M.S. Beagle: H.M.S. Beagle Destination:Destination: Voyage around the world. Voyage around the world. Findings:Findings: evidence to propose a revolutionary evidence to propose a revolutionary

hypothesis about how life changes over timehypothesis about how life changes over time

Theory of Natural Selection ‑ DarwinismTheory of Natural Selection ‑ Darwinism Charles Robert Darwin (1809‑1880) was born on February Charles Robert Darwin (1809‑1880) was born on February

12, 1809 in England. He had his early education at Shrewsbury. He 12, 1809 in England. He had his early education at Shrewsbury. He had great love for dogs and would hunt birds, which his father had great love for dogs and would hunt birds, which his father dislikes. After his school education, Darwin was sent to medical dislikes. After his school education, Darwin was sent to medical school at Edinburgh in 1815.He did not find any interest in medical school at Edinburgh in 1815.He did not find any interest in medical studies and after two years he discontinued. His father then studies and after two years he discontinued. His father then suggested him to become a clergyman, which appealed him. Since it suggested him to become a clergyman, which appealed him. Since it was necessary to have a degree for this position, Charles Darwin was necessary to have a degree for this position, Charles Darwin enrolled himself for a degree at Cambridge in 1828 and graduated in enrolled himself for a degree at Cambridge in 1828 and graduated in 1831.At that time he cam into contact with eminent persons among 1831.At that time he cam into contact with eminent persons among those Dr. Henslow (An eminent Botanist) is one.Dr.Henslow those Dr. Henslow (An eminent Botanist) is one.Dr.Henslow suggested Charles Darwin for a voyage of exploration on the famous suggested Charles Darwin for a voyage of exploration on the famous H.M.S. Beagle. In this ship he visited most of the islads of the H.M.S. Beagle. In this ship he visited most of the islads of the Atlantic ocean, coasts of South America and some islands of South Atlantic ocean, coasts of South America and some islands of South pacific ocean of which Galapagos islands are the most important.pacific ocean of which Galapagos islands are the most important.

This voyage enabled him to publish many important books This voyage enabled him to publish many important books later on. In the year 1836 he read an essay of Malthus on later on. In the year 1836 he read an essay of Malthus on population. Malthusian theory suggested him that struggle population. Malthusian theory suggested him that struggle for existence among organisms (plants and animals) would for existence among organisms (plants and animals) would finally lead to natural selection of the fittest among them. finally lead to natural selection of the fittest among them. Darwin first wrote his theory in 1842.He expanded the Darwin first wrote his theory in 1842.He expanded the manuscript in 1884 by adding more data. Later on he manuscript in 1884 by adding more data. Later on he published his"Origin of species” Darwin also expressed published his"Origin of species” Darwin also expressed his views along with Dr. Wallace in the research article his views along with Dr. Wallace in the research article published in the " proceedings of the linnaean society". In published in the " proceedings of the linnaean society". In 1859, his views were collected from his letters to Asa 1859, his views were collected from his letters to Asa Gray (a famous American Botanist).The views of Darwin Gray (a famous American Botanist).The views of Darwin are now known as Darwinism. are now known as Darwinism.

Darwin's PostulatesDarwin's Postulates Darwinism is based on the following important Darwinism is based on the following important

postulates they are,postulates they are, 1. Multiplication of individuals of a species in 1. Multiplication of individuals of a species in

geometric proportions.geometric proportions. 2. Occurrence of variation 2. Occurrence of variation 3. Operation of Natural selection to selection 3. Operation of Natural selection to selection a. Struggle for existence a. Struggle for existence

Intra specific, Inter specific & against Intra specific, Inter specific & against

environmentenvironment b) Survival of the fittest.b) Survival of the fittest.

Over productionOver production As far as the multiplication is concerned nature is prodigal.A As far as the multiplication is concerned nature is prodigal.A

salamon (a fish) produces 28,000,000 eggs in a season, An Oyster salamon (a fish) produces 28,000,000 eggs in a season, An Oyster produces 114,000,000 eggs at a single spawning.Ascaris lay eggs produces 114,000,000 eggs at a single spawning.Ascaris lay eggs 7,00,000 eggs in 24 hours.Frog lays many hundreds of egg in each 7,00,000 eggs in 24 hours.Frog lays many hundreds of egg in each season. If it develops in a geometric proportion it is needless to says season. If it develops in a geometric proportion it is needless to says that the whole earth will soon be covered by a single that the whole earth will soon be covered by a single individuals.These examples can be shown in each ascaris, fishes, individuals.These examples can be shown in each ascaris, fishes, insects etc.insects etc.

The elephant is the slowest breeder among mammals.It The elephant is the slowest breeder among mammals.It begins reproduce at its 40th year.Stops at its 90th years. Producing begins reproduce at its 40th year.Stops at its 90th years. Producing approximately 6 younger ones in its lifetime. It is thus calculated approximately 6 younger ones in its lifetime. It is thus calculated after 750 years there would be 19 millions of elephants alive.after 750 years there would be 19 millions of elephants alive.

If each individual develops in such a proportion struggle If each individual develops in such a proportion struggle arises for space, food and living conditions.arises for space, food and living conditions.

Struggle For Existence Struggle For Existence Due to geometrical multiplication of individuals, the fixed and spaces Due to geometrical multiplication of individuals, the fixed and spaces

become limited.As a result a struggle for existence follows.The struggle may occur become limited.As a result a struggle for existence follows.The struggle may occur between the individuals of same species or different species or due to environmental between the individuals of same species or different species or due to environmental factors.The three kinds of struggles are,factors.The three kinds of struggles are,

1. Intra Specific Struggle1. Intra Specific Struggle If a competition is between the members of the same species then the If a competition is between the members of the same species then the

struggle is intra specific struggle. e.g., Aquarium fishes eating their own young struggle is intra specific struggle. e.g., Aquarium fishes eating their own young ones as soon as they are given birth. Numerous young trees may grow under a ones as soon as they are given birth. Numerous young trees may grow under a parent tree.parent tree.

2. Inter Specific Struggle 2. Inter Specific Struggle Here struggle between individuals of different species occurs. Here struggle between individuals of different species occurs. Eg., Lion feeding on sheep, birds eating insects, i.e the stronger animals Eg., Lion feeding on sheep, birds eating insects, i.e the stronger animals

will feed on weaker ones.will feed on weaker ones. 3. Environmental Struggle3. Environmental Struggle Here the struggle occurs between the organism with various environmental Here the struggle occurs between the organism with various environmental

factors like excess of drought, moisture, extremes of heat and cold, lightning, factors like excess of drought, moisture, extremes of heat and cold, lightning, earthquakes, floods, volcanoes, diseases etc. Such natural calamities result in the earthquakes, floods, volcanoes, diseases etc. Such natural calamities result in the death of a large number of animals.death of a large number of animals.

VariationsVariations Variation is a natural phenomenon. No two Variation is a natural phenomenon. No two

individuals of a same species are exactly similar. They individuals of a same species are exactly similar. They will differ at least in few aspects. A group of will differ at least in few aspects. A group of individuals (a population) of a species may show a individuals (a population) of a species may show a definite pattern of variation differentiating it from other definite pattern of variation differentiating it from other population of the same species. These are termed as population of the same species. These are termed as subspecies by taxonomists and were called "Incipient subspecies by taxonomists and were called "Incipient species" by Darwin. These `incipient species' will reach species" by Darwin. These `incipient species' will reach the status of a species in course of time by evolution. the status of a species in course of time by evolution. This is how a new species is formed due to variations This is how a new species is formed due to variations according to Darwin. according to Darwin.

Darwin reported two kinds of variations they areDarwin reported two kinds of variations they are

Survival of the fittest and Natural selectionSurvival of the fittest and Natural selection Darwin observed that only those animals Darwin observed that only those animals

which have favourable variations or fittest which have favourable variations or fittest adaptations will survive in the struggle for life. adaptations will survive in the struggle for life. In other words nature will select only those In other words nature will select only those animals to survive which have fittest adaptations animals to survive which have fittest adaptations and other which will have unfavourable and other which will have unfavourable variations will be eliminated.Thus natural variations will be eliminated.Thus natural selection acts on animals and only the best are selection acts on animals and only the best are selected and its action is automatic.selected and its action is automatic.

1. 1. Continuous VariationContinuous Variation A character appears and develops gradually generation after A character appears and develops gradually generation after

generation. This variation will be selected by nature if it is useful.generation. This variation will be selected by nature if it is useful. 2. Discontinuous Variation2. Discontinuous Variation These variations appear all of a sudden and show no gradation. These variations appear all of a sudden and show no gradation.

These were also known as "Sports" which were later called " Mutations" These were also known as "Sports" which were later called " Mutations" by Devries.by Devries.

According to Darwin discontinuous varieties were of no use in According to Darwin discontinuous varieties were of no use in evolution.He believed that the continuous variations are important for evolution.He believed that the continuous variations are important for evolution because such variations will appear suddenly and will mostly evolution because such variations will appear suddenly and will mostly be harmful and therefore will not be selected again.Darwin cited be harmful and therefore will not be selected again.Darwin cited dinosaurs as example for discontinuous variation.The dinosaures became dinosaurs as example for discontinuous variation.The dinosaures became extinct due to their enormous size.On the other hand if a character extinct due to their enormous size.On the other hand if a character develops gradually generation after generation (continuous variation) and develops gradually generation after generation (continuous variation) and if it proves useful it will be selected by nature.The long neck giraffe was if it proves useful it will be selected by nature.The long neck giraffe was cited as an example for continuous variation by Darwin.cited as an example for continuous variation by Darwin.

Patterns of Diversity

Darwin visited Argentina and Australia which had Darwin visited Argentina and Australia which had similar grassland ecosystems. similar grassland ecosystems.

those grasslands were inhabited by very different those grasslands were inhabited by very different animals. animals.

neither Argentina nor Australia was home to the neither Argentina nor Australia was home to the sorts of animals that lived in European grasslands.sorts of animals that lived in European grasslands.

Patterns of Diversity

Darwin posed challenging questions. Darwin posed challenging questions. Why were there no rabbits in Australia, despite the Why were there no rabbits in Australia, despite the

presence of habitats that seemed perfect for them?presence of habitats that seemed perfect for them?

Why were there no kangaroos in England?Why were there no kangaroos in England?

Living Organisms and Fossils

Darwin collected the preserved remains of Darwin collected the preserved remains of ancient organisms, called ancient organisms, called fossils. .

Some of those fossils resembled organisms that Some of those fossils resembled organisms that were still alive today.were still alive today.

Living Organisms and Fossils   Others looked completely unlike any creature he had Others looked completely unlike any creature he had

ever seen. ever seen.

As Darwin studied fossils, new questions arose. As Darwin studied fossils, new questions arose. Why had so many of these species disappeared? Why had so many of these species disappeared?

How were they related to living species?How were they related to living species?

The Galapagos Island The smallest, lowest islands were hot, The smallest, lowest islands were hot,

dry, and nearly barren-Hood Island-sparse dry, and nearly barren-Hood Island-sparse vegetationvegetation

The higher islands had greater rainfall and The higher islands had greater rainfall and a different assortment of plants and a different assortment of plants and animals-Isabela- Island had rich animals-Isabela- Island had rich vegetationvegetation..

The Galapagos Island

Darwin was fascinated in particular by the land Darwin was fascinated in particular by the land tortoises and marine iguanas in the Galápagos. tortoises and marine iguanas in the Galápagos.

Giant tortoises varied in predictable ways from Giant tortoises varied in predictable ways from one island to another.one island to another.

The shape of a tortoise's shell could be used to The shape of a tortoise's shell could be used to identify which island a particular tortoise identify which island a particular tortoise inhabited. inhabited.

Animals found in the Galapagos

Land TortoisesLand Tortoises

Darwin FinchesDarwin Finches

Blue-Footed BoobyBlue-Footed Booby

Marine IguanasMarine Iguanas

The Journey Home

Darwin Observed that characteristics Darwin Observed that characteristics of many plants and animals vary of many plants and animals vary greatly among the islandsgreatly among the islands

Hypothesis:Hypothesis: Separate species may Separate species may have arose from an original ancestorhave arose from an original ancestor

Ideas that shaped Darwin’s Thinking James Hutton:James Hutton: 1795 Theory of 1795 Theory of

Geological changeGeological change Forces change Forces change

earth’s surface earth’s surface shapeshape

Changes are slowChanges are slow Earth much older Earth much older

than thousands of than thousands of yearsyears

Ideas that Shaped Darwin’s Thinking Charles LyellCharles Lyell Book: Book: Principles of Principles of

GeographyGeography Geographical features Geographical features

can be built up or torn can be built up or torn downdown

Darwin thought if Darwin thought if earth changed over earth changed over time, what about life?time, what about life?

Population Growth Thomas MalthusThomas Malthus--

19th century English 19th century English economisteconomist

If population grew If population grew (more Babies born (more Babies born than die)than die) Insufficient living Insufficient living

spacespace Food runs outFood runs out Darwin applied this Darwin applied this

theory to animalstheory to animals

Publication of Orgin of Species

Russel Wallace wrote Russel Wallace wrote an essay summarizing an essay summarizing evolutionary change evolutionary change from his field work in from his field work in MalaysiaMalaysia

Gave Darwin the drive Gave Darwin the drive to publish his findingsto publish his findings

Natural Selection & Artificial Selection Natural variationNatural variation--differences among --differences among

individuals of a speciesindividuals of a species

Artificial selectionArtificial selection- nature provides the - nature provides the variation among different organisms, and variation among different organisms, and humans select those variations they find humans select those variations they find

usefuluseful..

Evolution by Natural Selection

The Struggle for ExistenceThe Struggle for Existence-members of -members of each species have to compete for food, each species have to compete for food, shelter, other life necessitiesshelter, other life necessities

Survival of the FittestSurvival of the Fittest-Some individuals -Some individuals better suited for the environmentbetter suited for the environment

Struggle For Existence & Survival of The Fittest

Natural Selection

Over time, natural Over time, natural selection results in selection results in changes in inherited changes in inherited characteristics of a characteristics of a population. These population. These changes increase a changes increase a species fitness in its species fitness in its environmentenvironment

Summary of Darwin’s Theory

Individuals in nature differ from one Individuals in nature differ from one anotheranother

Organisms in nature produce more Organisms in nature produce more offspring than can survive, and many of offspring than can survive, and many of those who do not survive do not reproduce.those who do not survive do not reproduce.

Summary of Darwin’s Theory

Because more organisms are produce than Because more organisms are produce than can survive, each species must struggle for can survive, each species must struggle for resourcesresources

Each organism is unique, each has Each organism is unique, each has advantages and disadvantages in the advantages and disadvantages in the struggle for existencestruggle for existence

Summary (cont.)

Individuals best suited for the environment Individuals best suited for the environment survive and reproduce most successfulsurvive and reproduce most successful

Species change over timeSpecies change over time

Summary (cont.)

Species alive today descended with modification Species alive today descended with modification from species that lived in the pastfrom species that lived in the past

All organisms on earth are united into a single All organisms on earth are united into a single family tree of life by common descentfamily tree of life by common descent

WEISMANNS GERMPLASM THEORYWEISMANNS GERMPLASM THEORY The germplasm theory is based on the concept that living bredies The germplasm theory is based on the concept that living bredies

are formed of two fundamentally different kinds of materials the are formed of two fundamentally different kinds of materials the germplasm and the somatoplasm is responsible for the germplasm and the somatoplasm is responsible for the development of reproductive parts and remains in the organism, development of reproductive parts and remains in the organism, sealed and secluded from the somatoplasm or the general body of sealed and secluded from the somatoplasm or the general body of the organism which develops out of the germplasm in course of the organism which develops out of the germplasm in course of time, the germplasm gives rise to the offspring in which again the time, the germplasm gives rise to the offspring in which again the germplasm remains separate from the new somatoplasm that it germplasm remains separate from the new somatoplasm that it develops. Thus the germplasm is a continuous stream from develops. Thus the germplasm is a continuous stream from generation to generation while the somatoplasm is formed a new generation to generation while the somatoplasm is formed a new at every generation and is discontinuous. In bisexual plants and at every generation and is discontinuous. In bisexual plants and animals at every generation the germplasm stream becomes a animals at every generation the germplasm stream becomes a confluence of the maternal and the pasernal streamconfluence of the maternal and the pasernal streams.s.

MUTATIONMUTATION Gene and ChromosomeGene and Chromosome Definition : Definition : Mutation may be defined as a heritable Mutation may be defined as a heritable

change in a gene or chromosome or change in the change in a gene or chromosome or change in the number of the chromosome. Mutation may occur number of the chromosome. Mutation may occur spontaneouly in nature (spontaneous mutation) or it spontaneouly in nature (spontaneous mutation) or it may be induced by artificial agents (Induced may be induced by artificial agents (Induced mutations)mutations)

Gene Mutation : Gene Mutation : The changes that alter the The changes that alter the structure of the gene at a molecular level is called structure of the gene at a molecular level is called Gene mutation. It is also called point mutation. i.e. Gene mutation. It is also called point mutation. i.e. permanent hertiable changes with in a gene.permanent hertiable changes with in a gene.

Chromosome MutationChromosome Mutation The structural changes occuring in The structural changes occuring in

chromosomes which affect the phenotype of chromosomes which affect the phenotype of the organism are called the organism are called chromosomal chromosomal mutations.mutations.

2. Gene Reaction2. Gene Reaction Hugo de VriesHugo de Vries Hugo de Vries (1848 - 1935) of Netherlands was born in Hugo de Vries (1848 - 1935) of Netherlands was born in

Haarlem in February 16, 1848, in Holland. de Vries was a Haarlem in February 16, 1848, in Holland. de Vries was a professor in plant physiology at the University of professor in plant physiology at the University of Amsterdam in 1881. He gave ‘mutation theory’ on his Amsterdam in 1881. He gave ‘mutation theory’ on his observations on observations on Oenothera lamarkianaOenothera lamarkiana. He noticed . He noticed "gigas" a large size and "nanella" a dwarf mutant. The "gigas" a large size and "nanella" a dwarf mutant. The mutant "gigas" had 28 chromosomes instead of 14 which mutant "gigas" had 28 chromosomes instead of 14 which is present in parental form. It was a tetraploid mutant. The is present in parental form. It was a tetraploid mutant. The mutations described by deVries in mutations described by deVries in Oenothera lamarckiana Oenothera lamarckiana is due to numerical and structural changes in is due to numerical and structural changes in chromosomes.chromosomes.

T. G. DobzhanskyT. G. Dobzhansky Theodosius Grigorievitch Dobzhansky was born Theodosius Grigorievitch Dobzhansky was born

in Nemirov, Russia on 25 January 1900. He began in Nemirov, Russia on 25 January 1900. He began his scientific career by studying the variation in his scientific career by studying the variation in natural populations of a type of beetles in Europe natural populations of a type of beetles in Europe and Asia. The morphological polymorphism of and Asia. The morphological polymorphism of these beetles led him to reject the usual naming of these beetles led him to reject the usual naming of separate races with geographical ranges. separate races with geographical ranges. Dobzhansky suggested to determine what was Dobzhansky suggested to determine what was responsible for maintaining the large amount of responsible for maintaining the large amount of genetic polymorphism within populations.genetic polymorphism within populations.

T.H.Morgan :T.H.Morgan : T.H.Morgan (1910) started his work on fruitfly T.H.Morgan (1910) started his work on fruitfly

Drosophila melanogasterDrosophila melanogaster. He reported sudden . He reported sudden appearance of white eyed males among red eyed appearance of white eyed males among red eyed male individuals. The gene for this character is male individuals. The gene for this character is located on X - chromosome and it express itself located on X - chromosome and it express itself in male individuals. He was the first to report in male individuals. He was the first to report mutation in mutation in Drosophila.Drosophila.

3. Molecular basis of gene mutation3. Molecular basis of gene mutation Mutation that occurs in the DNA molecule is Mutation that occurs in the DNA molecule is

called molecular gene mutation.called molecular gene mutation. This may be of different types :This may be of different types : Transition : Transition : - A purine base (A) is replaced by - A purine base (A) is replaced by

another purine base (G) or pyrimidine base (T) is another purine base (G) or pyrimidine base (T) is substituted by another pyrimidine base (C). They substituted by another pyrimidine base (C). They occur due to (a) Deamination (b) Base Analogues.occur due to (a) Deamination (b) Base Analogues.

(a) (a) Deamination : Deamination : Some chemicals like nitrous Some chemicals like nitrous acid cause mutation due to deamination of DNA acid cause mutation due to deamination of DNA bases. The amino group (-NH2) of a DNA is bases. The amino group (-NH2) of a DNA is replaced by a hydroxyl (-OH) group.Because of replaced by a hydroxyl (-OH) group.Because of this Adenine instead of pairing with Thymine, this Adenine instead of pairing with Thymine, pairs with Cytosine. Adenine -® hypoxanthine, pairs with Cytosine. Adenine -® hypoxanthine, which pairs with cytosinewhich pairs with cytosine

(b) (b) Base Analogues : Base Analogues : Analogue is a substance that Analogue is a substance that corresponds to the normal DNA base in several corresponds to the normal DNA base in several characteristics. Because of this the normal base characteristics. Because of this the normal base may be replaced by the analogue.may be replaced by the analogue.

TYPES OF MUTATIONSTYPES OF MUTATIONS (1) (1) Spontaneous mutation : Spontaneous mutation : It occurs naturally It occurs naturally

without any artificial induction.Spontaneous without any artificial induction.Spontaneous mutations arise from errors in DNA replication mutations arise from errors in DNA replication and spontaneous lesions.Natural exposure of an and spontaneous lesions.Natural exposure of an organism to certain environmental factors such as organism to certain environmental factors such as U-V light may bring about spontaneous mutation.U-V light may bring about spontaneous mutation.

(2) (2) Induced mutation : Induced mutation : Mutations which are Mutations which are artifically induced with the help of mutagenic agents artifically induced with the help of mutagenic agents are called induced mutations.are called induced mutations.

(3) (3) Somatic mutation : Somatic mutation : Mutations in somatic cell or Mutations in somatic cell or non-reproductive cells are called somatic mutations non-reproductive cells are called somatic mutations e.g., Mole in humans, they are not transmitted to e.g., Mole in humans, they are not transmitted to progenyprogeny

(4) (4) Germinal mutations : Germinal mutations : Genes and chromosomes Genes and chromosomes can mutate in reproductive tissues and these changes can mutate in reproductive tissues and these changes are called germinal mutations; they are transmitted are called germinal mutations; they are transmitted to the progeny.e.g., X - linked haemophilia in the to the progeny.e.g., X - linked haemophilia in the European royal families.European royal families.

4. Induced Mutation4. Induced Mutation The mutations which can be induced artifically in The mutations which can be induced artifically in

the living organisms using physical or chemical the living organisms using physical or chemical agents are called induced mutations.Such agents agents are called induced mutations.Such agents are called mutagenic agents.are called mutagenic agents.

Mutagenic agents : Mutagenic agents : They are of following types They are of following types (I) Physical mutagens (II) Chemical mutagens(I) Physical mutagens (II) Chemical mutagens

(i) Physical mutagens :(i) Physical mutagens : (1) Radiation : (1) Radiation : (i) Non-ionizing radiation such as (i) Non-ionizing radiation such as

U-V rays, (ii) Ionizing radiation x-rays,U-V rays, (ii) Ionizing radiation x-rays, gamma rays, beta rays, protons, neutrons and alpha gamma rays, beta rays, protons, neutrons and alpha

rays.rays. (ii) Chemical mutagens :(ii) Chemical mutagens : Many chemicals can be used for inducing mutations. Many chemicals can be used for inducing mutations.

C. Auerbach was the first to find that mutation can C. Auerbach was the first to find that mutation can also be induced due to certain chemicals. She made also be induced due to certain chemicals. She made this discovery during world war II. The chemicals this discovery during world war II. The chemicals used for inducing mutations were Ethyl methane used for inducing mutations were Ethyl methane sulphonate, caffeine, phenol, mustard gas etc.sulphonate, caffeine, phenol, mustard gas etc.

5. Chromosomal aberrations5. Chromosomal aberrations The structural changes which affect the phenotype of The structural changes which affect the phenotype of

the organisms is called chromosomal aberration. The the organisms is called chromosomal aberration. The structural changes are (1) Deletions (2) Duplications structural changes are (1) Deletions (2) Duplications (3) Inversions (4) Translocations.(3) Inversions (4) Translocations.

(1) (1) Deletions : Deletions : It is a type of intrachromosomal It is a type of intrachromosomal aberration. Either terminal or intermediate portion aberration. Either terminal or intermediate portion may get deleted.Eg. Maize.E.g., In human beings may get deleted.Eg. Maize.E.g., In human beings Cri-du-chat’s syndrome. Deletion was in a segment Cri-du-chat’s syndrome. Deletion was in a segment of chromosome 5.of chromosome 5.

Fig. DeletionFig. Deletion   

(2) Duplication : (2) Duplication : It is an intra-chromosomal It is an intra-chromosomal aberration (within a chromosome). It occurs aberration (within a chromosome). It occurs when a segment of the chromosome is when a segment of the chromosome is represented 2 or more times in a represented 2 or more times in a chromosome of a homologous segment.e.g., chromosome of a homologous segment.e.g., Bar-eye in Drosophila:Bar-eye in Drosophila:

(3) Inversion : (3) Inversion : It is an intra -chromosomal It is an intra -chromosomal aberration (within a chromosome) when there are aberration (within a chromosome) when there are two breaks the intercalary segment is inverted to two breaks the intercalary segment is inverted to 180 degrees.180 degrees.

6. Evolutionary significance of mutation6. Evolutionary significance of mutation The process of speciation is the most important The process of speciation is the most important

significance of mutations. Artificial induction and significance of mutations. Artificial induction and selection of mutants increased a pool of variability selection of mutants increased a pool of variability to allow more rapid development in plants with to allow more rapid development in plants with desirable traits. Polyploidy results in the formation desirable traits. Polyploidy results in the formation of new species. Thus mutations are responsible for of new species. Thus mutations are responsible for evolution of new species.evolution of new species.

7. Applied Mutation7. Applied Mutation Applied mutation is making use of mutation procedure to Applied mutation is making use of mutation procedure to

create improved varieties of plants and new strains of create improved varieties of plants and new strains of animals. New strains of microorganisms show enchanced animals. New strains of microorganisms show enchanced yields or produce novel products. Beneficial mutations are yields or produce novel products. Beneficial mutations are used in modern agriculture or the industrial fermentation. used in modern agriculture or the industrial fermentation. Mutation breeding in India has been in progress. The Mutation breeding in India has been in progress. The establishment of Gamma garden of Bose Research Institute, establishment of Gamma garden of Bose Research Institute, Calcutta in 1959 & at IARI New Delhi 1960 has opened a Calcutta in 1959 & at IARI New Delhi 1960 has opened a new vista for crop improvement.By the application of new vista for crop improvement.By the application of mutation techniques, new varieties with desirable qualities mutation techniques, new varieties with desirable qualities have been developed. e.g., Sharbati sonora in wheat, Barley have been developed. e.g., Sharbati sonora in wheat, Barley varieties, etc.varieties, etc.

Antibiotics Production : Antibiotics Production : Increased yield of Increased yield of penicillin from penicillin from Penicillium Penicillium is possible by is possible by developing newer strains by mutation.developing newer strains by mutation.

A A landracelandrace is a local variety of a is a local variety of a domesticated animal or plant species which has developed largely animal or plant species which has developed largely by natural processes, by adaptation to the natural and by natural processes, by adaptation to the natural and cultural environment in which it lives. It differs from cultural environment in which it lives. It differs from a formal a formal breed which has been bred deliberately to which has been bred deliberately to conform to a particular standard type. Landraces are conform to a particular standard type. Landraces are usually more usually more genetically and and physically diverse than diverse than formal breeds. Many formal breeds originated from formal breeds. Many formal breeds originated from landraces, and sometimes a particular type has both landraces, and sometimes a particular type has both landrace and formal breed populations. Sometimes a landrace and formal breed populations. Sometimes a formalised breed retains the "landrace" name, formalised breed retains the "landrace" name, despite no longer being a true landrace.despite no longer being a true landrace.

Several definitions of the term landrace have been used in botanical Several definitions of the term landrace have been used in botanical application.application.

"Landrace populations are often highly variable in appearance, but "Landrace populations are often highly variable in appearance, but they are each identifiable they are each identifiable morphologically and have a certain genetic and have a certain genetic integrity. Farmers usually give them local names. A landrace has integrity. Farmers usually give them local names. A landrace has particular properties or characteristics. Some are considered early particular properties or characteristics. Some are considered early maturing and some late. Each has a reputation for adaptation to maturing and some late. Each has a reputation for adaptation to particular particular soil types according to the traditional peasant soil according to the traditional peasant soil classifications, e.g. heavy or light, warm or cold, dry or wet, strong classifications, e.g. heavy or light, warm or cold, dry or wet, strong or weak. They also may be classified according to expected usage; or weak. They also may be classified according to expected usage; among cereals, different landraces are used for flour, for porridge, for among cereals, different landraces are used for flour, for porridge, for ''bulgur', and for malt to make beer, etc. All components of the ', and for malt to make beer, etc. All components of the population are adapted to local climatic conditions, cultural practices, population are adapted to local climatic conditions, cultural practices, and disease and pests."and disease and pests."[1] But most important, they are genetically But most important, they are genetically diverse. They are balanced diverse. They are balanced populations – variable, in equilibrium – variable, in equilibrium with both environment and with both environment and pathogens and genetically dynamic’. and genetically dynamic’.[2]

The term "landrace" has additionally been The term "landrace" has additionally been defined asdefined as

"An "An autochthonous landrace is a variety landrace is a variety with a high capacity to tolerate biotic and with a high capacity to tolerate biotic and abiotic stress, resulting in a high yield abiotic stress, resulting in a high yield stability and an intermediate yield level stability and an intermediate yield level under a low input agricultural system."under a low input agricultural system."[3]

Evolutionary processEvolutionary process Landraces are grown from seeds which have not been systematically Landraces are grown from seeds which have not been systematically

selected and marketed by seed companies or developed by plant selected and marketed by seed companies or developed by plant breeders. Landraces will refer to all those cultigens that are highly breeders. Landraces will refer to all those cultigens that are highly heterogeneous, but with enough characteristics in common to permit , but with enough characteristics in common to permit their recognition as a group. This will include all cultigens cultivated their recognition as a group. This will include all cultigens cultivated without any specific without any specific nomenclature and value. A landrace identified and value. A landrace identified with a unique feature and selected for uniformity over a period of with a unique feature and selected for uniformity over a period of time for maintenance of the characteristic features of the population time for maintenance of the characteristic features of the population can evolve into a farmers’ variety or even a modern cultivar as in can evolve into a farmers’ variety or even a modern cultivar as in many crops; for example, Maruti in the case of many crops; for example, Maruti in the case of pigeon peas..

Conversely, a modern Conversely, a modern cultivar grown over time by the farmers and grown over time by the farmers and not maintained as per the principles of maintenance breeding can not maintained as per the principles of maintenance breeding can ‘evolve’ into a landrace.‘evolve’ into a landrace.

A significant proportion of the world’s farmers grow landraces. Data collected A significant proportion of the world’s farmers grow landraces. Data collected for a study of the spread of cereal agriculture into Europe showed that landraces for a study of the spread of cereal agriculture into Europe showed that landraces have largely fallen out of use in Europe. European cereal landraces were mainly have largely fallen out of use in Europe. European cereal landraces were mainly grown by our ancestors before breeders started to improve the varieties in the grown by our ancestors before breeders started to improve the varieties in the 20th century.20th century.

Some landraces have survived in Europe, having been handed on from one Some landraces have survived in Europe, having been handed on from one generation of farmers to the next. Elsewhere, landraces and traditional varieties generation of farmers to the next. Elsewhere, landraces and traditional varieties have been revived by enthusiasts who seek to preserve our agricultural and food have been revived by enthusiasts who seek to preserve our agricultural and food heritage. Landraces and traditional varieties are valued as the source of heritage. Landraces and traditional varieties are valued as the source of ingredients in traditional food and traditional drinks or as raw materials for ingredients in traditional food and traditional drinks or as raw materials for thatching.thatching.

There have been systematic efforts to preserve European cereal landraces either There have been systematic efforts to preserve European cereal landraces either in germplasm collections or in situ. The activities of these collections are in germplasm collections or in situ. The activities of these collections are coordinated by coordinated by Bioversity International. This organisation coordinates . This organisation coordinates information on conservation activities, including a searchable online database of information on conservation activities, including a searchable online database of germplasm collections. However, more needs to be done, Regine Anderson germplasm collections. However, more needs to be done, Regine Anderson argues, because plant genetic variety depends on a diversity of landraces. argues, because plant genetic variety depends on a diversity of landraces. An issue of survival

The terms ‘landrace’ and ‘traditional variety’ are sometimes used The terms ‘landrace’ and ‘traditional variety’ are sometimes used interchangeably.interchangeably.

AnimalsAnimals Animal landraces occur in many species of domestic animals. A Animal landraces occur in many species of domestic animals. A

landrace does not imply so much a landrace does not imply so much a breed as a as a typetype of animal. of animal. Examples include the Examples include the Norwegian Forest Cat, , Shetland sheep, and , and Welsh Mountain sheep. Often, from within a landrace a small . Often, from within a landrace a small number of animals have been selected to found a formal pedigree number of animals have been selected to found a formal pedigree breed, usually of the same name as the landrace. "Landrace" pigs breed, usually of the same name as the landrace. "Landrace" pigs (such as (such as Danish Landrace) are breeds derived from landraces. ) are breeds derived from landraces. When people select animals to create a highly consistent When people select animals to create a highly consistent purebred breed, they often select for a consistent appearance rather than breed, they often select for a consistent appearance rather than behavior or adaptability to a given environment. When this behavior or adaptability to a given environment. When this happens, defining characteristics of the landrace may be lost.happens, defining characteristics of the landrace may be lost.

DogsDogs Dog landraces and dog breeds derived from them vary greatly, depending on their landraces and dog breeds derived from them vary greatly, depending on their

origins and purpose. Three examples are the origins and purpose. Three examples are the Border Collie, , Armenian Gampr dog and and Saluki. The Border Collie landrace is used as a . The Border Collie landrace is used as a herding dog and varies in and varies in appearance: ears pricked upright to nearly dropped, varied fullnesses of coat, and appearance: ears pricked upright to nearly dropped, varied fullnesses of coat, and so on. However, they are recognized as Border Collies by their general so on. However, they are recognized as Border Collies by their general appearance and most of all by their unique manner of herding sheep. In contrast to appearance and most of all by their unique manner of herding sheep. In contrast to the landrace, in the Border Collie the landrace, in the Border Collie breedbreed show-quality individuals very closely show-quality individuals very closely match a "breed standard" appearance but might not be particularly good at match a "breed standard" appearance but might not be particularly good at herding sheep and might not have a coat suitable for outdoor life. Similarly, the herding sheep and might not have a coat suitable for outdoor life. Similarly, the Saluki landrace of the landrace of the Middle East excels in running down excels in running down game across open across open tracts of hot desert, but show-quality individuals of the breed might not be able to tracts of hot desert, but show-quality individuals of the breed might not be able to chase and catch chase and catch hares in the desert. The now extinct in the desert. The now extinct St. John's Water Dog landrace was native to the island of Newfoundland. It was the foundational breed landrace was native to the island of Newfoundland. It was the foundational breed for a number of purpose-bred dogs, such as the Labrador Retriever, and for a number of purpose-bred dogs, such as the Labrador Retriever, and

Chesapeake Chesapeake Bay Retriever, as well as the Newfoundland DogBay Retriever, as well as the Newfoundland Dog

HorsesHorses Although the term "landrace" is rarely used in modern horse Although the term "landrace" is rarely used in modern horse

breeding, numerous landraces of horses do exist. Some of these are breeding, numerous landraces of horses do exist. Some of these are predominantly feral types, but the majority are fully domesticated predominantly feral types, but the majority are fully domesticated working animals. Notable landraces from which pedigreed breeds working animals. Notable landraces from which pedigreed breeds have been formed include the New Forest pony and Exmoor pony. have been formed include the New Forest pony and Exmoor pony. The New Forest mares living semi-wild on the New Forest are The New Forest mares living semi-wild on the New Forest are largely non-pedigreed landrace animals, while the stallions, and largely non-pedigreed landrace animals, while the stallions, and those kept as fully domesticated animals and bred for showing are those kept as fully domesticated animals and bred for showing are a formal breed. Aficionados of some horse breeds claim them to be a formal breed. Aficionados of some horse breeds claim them to be "pure" and virtually unchanged from their original wild prototype "pure" and virtually unchanged from their original wild prototype or landrace. Such breeds include the Arabian horse and the or landrace. Such breeds include the Arabian horse and the Andalusian horse, and a number of feral breeds (such as the Andalusian horse, and a number of feral breeds (such as the Banker horse) that are restricted to islands.Banker horse) that are restricted to islands.

CattleCattle Examples of landrace cattle include Examples of landrace cattle include

Pineywoods, Florida Cracker and Randall Pineywoods, Florida Cracker and Randall cattle.cattle.[7][7]

Landraces or Original Cultivars:Landraces or Original Cultivars: Landrace genetics are grown from seeds which have not been Landrace genetics are grown from seeds which have not been

systematically selected and marketed by seed companies or systematically selected and marketed by seed companies or developed by plant breeders. They are not necessarily homogeneous developed by plant breeders. They are not necessarily homogeneous (similar) but they exhibit enough characteristics in common to (similar) but they exhibit enough characteristics in common to permit their recognition as a group. A landrace identified with a permit their recognition as a group. A landrace identified with a unique feature and selected for uniformity over a period of time for unique feature and selected for uniformity over a period of time for maintenance of the characteristic features of the population can maintenance of the characteristic features of the population can evolve into a farmers' variety or even a modern cultivar. Conversely, evolve into a farmers' variety or even a modern cultivar. Conversely, a modern cultivar grown over a time by farmers outdoors that is not a modern cultivar grown over a time by farmers outdoors that is not maintained as per the principles of normal maintenance breeding maintained as per the principles of normal maintenance breeding can evolve into a landrace.can evolve into a landrace.

Original cultivars are those strains which are bred and introduced to Original cultivars are those strains which are bred and introduced to the cannabis community that are distinct from other strains of the cannabis community that are distinct from other strains of cannabis. Usually, but not always, original cultivars retain those cannabis. Usually, but not always, original cultivars retain those distinct characteristics when breeding with them.distinct characteristics when breeding with them.

Awareness of the need for biodiversity conservation is now Awareness of the need for biodiversity conservation is now universally accepted, but most often recent conservation universally accepted, but most often recent conservation activities have focused on wild species. Crop species and the activities have focused on wild species. Crop species and the diversity between and within them has significant socioeconomic diversity between and within them has significant socioeconomic as well as heritage value. The bulk of genetic diversity in as well as heritage value. The bulk of genetic diversity in domesticated species is located in traditional varieties maintained domesticated species is located in traditional varieties maintained by traditional farming systems. These traditional varieties, by traditional farming systems. These traditional varieties, commonly referred to as landraces, are severely threatened by commonly referred to as landraces, are severely threatened by genetic extinction primarily due to their replacement by modern genetic extinction primarily due to their replacement by modern genetically uniform varieties. The conservation of landrace genetically uniform varieties. The conservation of landrace diversity has been hindered in part by the lack of an accepted diversity has been hindered in part by the lack of an accepted definition to define the entity universally recognized as definition to define the entity universally recognized as landraces. Without a definition it would be impossible to prepare landraces. Without a definition it would be impossible to prepare an inventory and without an inventory changes in landrace an inventory and without an inventory changes in landrace constituency could not be recognized over time. constituency could not be recognized over time.

Therefore, based on a literature review, workshop discussion and Therefore, based on a literature review, workshop discussion and interviews with key informants, common characteristics of landraces interviews with key informants, common characteristics of landraces were identified, such as: historical origin, high genetic diversity, were identified, such as: historical origin, high genetic diversity, local genetic adaptation, recognizable identity, lack of formal local genetic adaptation, recognizable identity, lack of formal genetic improvement, and whether associated with traditional genetic improvement, and whether associated with traditional farming systems. However, although these characteristics are farming systems. However, although these characteristics are commonly present they are not always all present for any individual commonly present they are not always all present for any individual landrace; several crop-specific exceptions were noted relating to landrace; several crop-specific exceptions were noted relating to crop propagation method (sexual or asexual), breeding system (self-crop propagation method (sexual or asexual), breeding system (self-fertilized or cross-fertilized species), length of formal crop fertilized or cross-fertilized species), length of formal crop improvement, seed management (selection or random propagation) improvement, seed management (selection or random propagation) and use. and use.

Phenotypic diversity among maize landraces is obvious in kernel Phenotypic diversity among maize landraces is obvious in kernel color, ear and kernel shape and size, and agronomic traits such as color, ear and kernel shape and size, and agronomic traits such as plant height and length of the growing cycle. Traditionally, this plant height and length of the growing cycle. Traditionally, this phenotypic diversity has been used to classify populations into phenotypic diversity has been used to classify populations into races. Currently, 59 races of maize have been described in races. Currently, 59 races of maize have been described in Mexico. According to DNA analyses, these races are organized as Mexico. According to DNA analyses, these races are organized as a continuum and their differentiation is mainly due to isolation by a continuum and their differentiation is mainly due to isolation by distance. Recent genetic studies of landraces in Oaxaca (Mexico) distance. Recent genetic studies of landraces in Oaxaca (Mexico) have shown that gene flow between maize populations is have shown that gene flow between maize populations is quantitatively important but that management of seed by farmers quantitatively important but that management of seed by farmers maintains strong agromorphological differentiation between maize maintains strong agromorphological differentiation between maize populations. In traditional agricultural systems, farmers play a populations. In traditional agricultural systems, farmers play a wide range of roles with regard to seed production and wide range of roles with regard to seed production and maintenance. maintenance.

They conserve the genetic resources; they select and plant seed from They conserve the genetic resources; they select and plant seed from their varieties; and, after harvest, they are the main consumers of their their varieties; and, after harvest, they are the main consumers of their products. In Mexico, the traditional system coexists with the modern products. In Mexico, the traditional system coexists with the modern agricultural sector but the subsistence-oriented system is much more agricultural sector but the subsistence-oriented system is much more widely distributed. In this system, landraces are the result of continued widely distributed. In this system, landraces are the result of continued evolution influenced by various factors: 1) Seed recycling: Saving seed evolution influenced by various factors: 1) Seed recycling: Saving seed from one season to the next is an almost universal practice.At least from from one season to the next is an almost universal practice.At least from the farmers perspective, seed selection may also be fundamental to the farmers perspective, seed selection may also be fundamental to maintaining the integrity of a landrace, which can be lost easily through maintaining the integrity of a landrace, which can be lost easily through hybridization; and 2) Seed flows: Mexican farmers commonly acquire hybridization; and 2) Seed flows: Mexican farmers commonly acquire seed from other farmers or sources within or outside the community for seed from other farmers or sources within or outside the community for several reasons, including experimentation, starting to farm, and lack of several reasons, including experimentation, starting to farm, and lack of sufficient seeds. Thus, traditional farmers actively maintain landraces as sufficient seeds. Thus, traditional farmers actively maintain landraces as dynamic entities. Farmers are willing to modify introduced maize dynamic entities. Farmers are willing to modify introduced maize cultivars through recurrent hybridization with the local genetic material cultivars through recurrent hybridization with the local genetic material (process of creolization) to improve their local performance and (process of creolization) to improve their local performance and consumer acceptability.consumer acceptability.

One of the innovative techniques that has been suggested for One of the innovative techniques that has been suggested for maintaining both genetic diversity and knowledge of farming systems maintaining both genetic diversity and knowledge of farming systems where traditional varieties are being lost involves the use of village-level where traditional varieties are being lost involves the use of village-level landrace custodians. Landraces are a crop cultivar or animal breed that landrace custodians. Landraces are a crop cultivar or animal breed that evolved with and has been genetically improved by traditional evolved with and has been genetically improved by traditional agriculturalists, but has not been influenced by modern breeding agriculturalists, but has not been influenced by modern breeding practices. At a limited number of key sites (perhaps between 100 and practices. At a limited number of key sites (perhaps between 100 and 500) in areas where diseases, pests, and pathogens strongly influence the 500) in areas where diseases, pests, and pathogens strongly influence the evolution of local crop varieties, individuals could be paid to grow a evolution of local crop varieties, individuals could be paid to grow a sample of the endangered native landraces. These farms would backstop sample of the endangered native landraces. These farms would backstop ex situex situ conservation efforts, maintain the potential for further evolution conservation efforts, maintain the potential for further evolution in important landraces, preserve knowledge of traditional farming in important landraces, preserve knowledge of traditional farming systems, and provide regional education on the importance of systems, and provide regional education on the importance of biodiversity conservation. If it seems economically inefficient to biodiversity conservation. If it seems economically inefficient to subsidize the subsidize the in situin situ maintenance of traditional landraces, consider how maintenance of traditional landraces, consider how often their loss is hastened by subsidies for such agricultural inputs as often their loss is hastened by subsidies for such agricultural inputs as fertilizers and pesticides. fertilizers and pesticides.