Neo darwinism - class-XI

Mutation is the primary source of new genetic variation in a population, providing the raw material upon which natural selection acts.

The presence of populations of a species in distant localities preventing the gene flow between them leads to geographical isolation. Incompatible differences in reproductive structures refer to as mechanical isolation. Different periods of attaiment of sexual maturity lead to temporal isolation. Hybrid sterility is a post zygotic isolation. Incompatible premating behaviour leading to no attraction between groups for mating is termed as behavioural isolation. Thus, the correct answer is C.

Reproductive isolation is brought about by the change in genetic material, gene pool and structure of genital organs. It prevents interbreeding between populations whether they are geographically isolated or living close together.

T.R. Malthus is famous for his book 'An Essay on the Principle of Population'.

Variations among individuals in a population are essential for natural selection and evolution to occur.

Evolutionary changes occur at the level of populations rather than individuals. A population is the smallest unit that can undergo evolutionary change over generations through shifts in allele frequencies.

Weismann gave theory of germplasm, according to which organisms are made up of two types of cells, the somatic cells and germ cells. Characters are transmitted through generations by germ cells and not somatic cells.

Saltation is an abrupt variation in the appearance of an organism, species, etc, usually caused by a genetic mutation (single step large mutation).  

Due to industrialization, the air pollution increased and lichens growth is declined so the black colored moths are well camouflaged themselves into the bark of trees that are covered by the industrial pollution and reproduce but white peppered moth are visible and more visible to predators so naturally declined. This is caused as humans evolve themselves but that increase the pollution and lead to a wrong or negative way for the moth.

Thomas Malthus' opinions regarding the struggle to survive helped to inspire Charles Darwin in his development of the theory of natural selection. Darwin noted that the population-food imbalance postulated by Malthus would lead to competition between offspring. He considered that some of those offspring would be better equipped for the struggle than others, and so would flourish. This "survival of the fittest" became the central theme to Darwin's developing theory. 

Heredity and variation are the fundamental pillars of evolution. Heredity ensures traits are passed on, while variation provides the raw material for selection to act upon.

The cosmozoic theory, also known as the theory of panspermia, proposes that life came to Earth from other parts of the universe in the form of resistant spores or germs. This hypothesis was proposed by Richter in 1865 and later supported by Arrhenius.

The modern synthetic theory of evolution is the result of the work of a number of scientists namely T. Dobzhansky, R.A. Fisher, J.B.S. Haldane, Swall Wright, Ernst Mayr, and G.L. Stebbins. Stebbins in his book, Process of Organic Evolution, discussed the synthetic theory.
It includes the following factors 

The numbat is a marsupial that occupies a similar ecological niche to the anteater, representing an example of convergent evolution where unrelated species develop similar traits.

Environmental change and isolation of groups of organisms play an important role in evolution. Isolation means that organisms of the same species are separated, and happens when there is something between the organisms that they can't cross. Organisms become isolated as a result of environmental change. The cause of isolation can be gradual, like when mountains or deserts form, or continents split apart. It can also be quick, such as organisms being blown to different places by a storm or tsunami (tidal waves).
When organisms become isolated the two groups are also not able to reproduce together, so variations and mutations that occur in one group are not necessarily found in the other group. The longer the groups are isolated, the more different they are. They eventually become different species. Moreover, if there is a change in the environment of one group it does not necessarily occur in the environment of the other. So they will evolve and adapt differently. So, the role of isolation in evolution is maintenance of species. Thus, option B is correct.
Differentiation of species or evolutionary divergence or extermination of species are not the roles of isolation in evolution. Thus, other options are wrong.

August Weismann proposed the germ plasm theory, which introduced the concept of determinants within the germ cells that control the development of traits, separating them from somatic cells.

The modern synthetic theory of evolution integrates Darwinian natural selection with Mendelian genetics, including mutation, recombination, and reproductive isolation as key drivers.

Darwin, in the fourth edition of his 'On the Origin of Species', wrote that the first author who in modern times has treated in a scientific spirit was Buffon a significant reference from the man known as the father of evolutionary theory. Buffon was known to have changed his views often during the course of his life and this is possibly why he is rarely referred to in the history of evolutionary thought. However, he is lauded by modern evolutionists as having posed significant questions about the development of life on Earth. Therefore, the correct answer is option B.

Late in the 1930s, Dobzhansky discovered "isolation mechanisms", i.e., finely-tuned sex traits, other genetic factors and to him physical barriers in the environment which impede gene flow between populations.  Without these mechanisms incorporated into evolutionary theory, it would under-explain the level of species-diversity found in nature. The theory of origin of isolation which stresses that nature is not in favour of hybridization was given by Dobzhansky. Thus, option C is correct. 

The modern synthetic theory of evolution is the result of the work of a number of scientists namely T. Dobzhansky, R.A. Fisher, J.B.S. Haldane, Swall Wright, Ernst Mayr, and G.L. Stebbins. Stebbins in his book, Process of Organic Evolution, discussed the synthetic theory. It includes the following factors - Gene mutations, Variation (Recombination), Heredity, Natural selection and Isolation. In addition, three accessory factors affect the working of these five basic factors. Migration of individuals from one population to another as well as hybridization between races or closely related species both increase the amount of genetic variability available to a population. The effects of chance acting on small populations may alter the way in which natural selection guides the course of evolution. Thus, option D is correct.

• The Modern Synthetic theory of Evolution explains the evolution of life in terms of genetic changes occurring in the populations that leads to the formation of new species. 
• It also explains the genetic population or Mendelian population, gene pool and the gene frequency
  
• Hence, According to the modern synthetic theory, the unit of evolution is a/an Population.
• So, the correct answer is 'Population'.

• The theory of evolution by natural selection, first formulated in Darwin's book "On the Origin of Species" in 1859, is the process by which organisms change over time as a result of changes in heritable physical or behavioural traits.
• Different characteristics tend to exist within any given population as a result of mutation, genetic recombination and other sources of genetic variation.
• Evolution occurs when evolutionary processes such as natural selection and genetic drift act on this variation, resulting in certain characteristics becoming more common or rare within a population. 
• Hence, Modern evolution theory involves Natural selection, Genetic variations and Isolation. 
• So, the correct answer is 'All of the above'.
  

Postmating isolating mechanism is any structure, physiological function, or developmental abnormality that prevents organisms of two different populations, once mating has occurred, from producing vigorous, fertile offspring. Postmating isolating mechanisms includes, gametic. Gametic incompatibility  (Sperm transfer takes place, but egg is not fertilized), Zygotic mortality (Egg is fertilized, but zygote does not develop), Hybrid inviability (Hybrid embryo forms, but of reduced viability), Hybrid sterility (Hybrid is viable, but resulting adult is sterile) and Hybrid breakdown (First generation (F$ _{1}$) hybrids are viable and fertile, but further hybrid generations (F$ _{2}$ and backcrosses) may be inviable or sterile). Thus, option D is correct and other options are wrong.

Natural selection acts by favoring advantageous variations and removing non-advantageous ones, which are less likely to survive and reproduce in a given environment.

Geographic isolation: In the fruit fly example, some fruit fly larvae were washed up on an island and speciation started because populations were prevented from interbreeding by geographic isolation. Scientists think that geographic isolation is a common way for the process of speciation to begin. Rivers change course, mountains rise, continents drift, organisms migrate and what was once a continuous population is divided into two or more smaller populations. So, a new species is formed from existing population when it is geographically isolated and not by different size of genitalia, different mating time and seasonal variations.

Evolution relies on genetic variation within a population. If all members were genetically identical, natural selection would have no variation to act upon, halting the evolutionary process.

Geographical isolation: The separation of two populations of the same species or breeding group by a physical barrier, such as a mountain or body of water. 

• Hugo de Vries in 1901 put forward a theory of evolution, called mutation theory. The theory states that evolution is a jerky process where new varieties and species are formed by mutations (discontinuous variations) that function as a raw material of evolution.
• Mutation theory can not explain the phenomenon of mimicry (i.e. the resemblance between mimic and model), protective coloration and relationship between position of nectaries in flowers and length of proboscis of insects that pollinate them.
  
  

Genetics and the Origin of Species is a 1937 book by the Ukrainian-American evolutionary biologist Theodosius Dobzhansky. It is regarded as one of the most important works of the modern evolutionary synthesis. The book popularized the work of population genetics to other biologists and influenced their appreciation for the genetic basis of evolution. In his book, Dobzhansky applied the theoretical work of Sewall Wright to the study of natural populations, allowing him to address evolutionary problems in a novel way during his time. Dobzhansky implements theories of mutation, natural selection and speciation throughout his book to explain habits of populations and the resulting effects on their genetic behavior. 

Genecology is the field of science, which uses theories from both ecology and genetics to modify according to the environment, while simultaneously developing resistance.  

First complete theory of evolution was given by Lamarck (1809). According to him, organism are capable of changing their form, size, colour, agility etc.

Biogenetic law was given by Ernst Haeckel in 1868 A.D. It states that ontogamy recaptulates phylogeny.

Heritability is the part of phenotype variation in a population. This can be attributed to genetic variations in the organisms in that population. This is the factor which describes the chances of evolution occurring in that population on the basis of the genetic differences. 

Physical separation of groups preventing the gene flow between them leads to geographical isolation. Incompatible differences in reproductive structures refer to as mechanical isolation. Different periods of attainment of sexual maturity lead to temporal isolation. Hybrid sterility is one of the post-zygotic isolation. Incompatible premating behaviour leading to no attraction between groups for mating is termed as behavioural isolation. Thus, the correct answer is E.

Physical separation of groups preventing the gene flow between them leads to geographical isolation. Incompatible differences in reproductive structures leading to prevention of cross-fertilization refer to as mechanical isolation. Different periods of attainment of sexual maturity lead to temporal isolation. Hybrid sterility is one of the post-zygotic isolation. Incompatible premating behaviour leading to no attraction between groups for mating is termed as behavioural isolation. Thus, the correct answer is B.

Genetic variation results in the evolution. It results due to mutation in the genetic material resulting in a permanent change. The process of natural selection directly creates genetic variation. Natural selection will change the allele frequencies in the population. This in turn will create genetic variation due to loss of certain alleles during natural selection. Mutation and genetic changes occur spontaneously and change in the environment does stimulate it. The higher the heterozygosity in a population, the higher genetic variation is seen in the population. 

Natural selection is a process governed by changes in environmental factors, these factors produce stress on the organisms. That compels the organisms to undergo changes, in case the organism undergoes changes suitable to the environment, that is, it is suited to survive in the environment will also pass on those traits to the next generation, until the next change occurs. This is natural selection.

"Nothing in Biology Makes Sense Except in the Light of Evolution" is a 1973 essay by the evolutionary biologist and Russian Orthodox Christian Theodosius Dobzhansky, criticising anti-evolution creationism and espousing theistic evolution.

An adaptation is a genetic change or variation that provides survival advantage to the organism.

Biston betularia is the common peppered moth, which was used to study industrial melanism in Britain. The melanic form and lighter coloured form are identical in all respects except for their body colour. Their frequency of occurrence changed with the industrial revolution in Britain.

In the 20th century conception of evolution being caused by a number of complex and often interacting processes. This is essentially a combination of Darwin's concept of natural selection, Mendel's basic genetics, along with the facts and theories of population genetics and molecular biology. So, this theory explains almost all factors related to organic evolution. Hence, this is the most accepted theory as compared to others.

Sterility of hybrid is never a pre - zygotic isolation mechanism.Hybrid zygotes sometimes develop into adults, such as mules (hybrids

between female horses and male donkeys), but the adults fail to develop

functional gametes and are sterile.

Members of species can interbreed naturally. This definition has some exceptions like animals obtained by interbreeding of animals of two species, this definition does not cover asexually reproducing organisms. However, among the options given best answer is Reproductive Isolation.

If species are geographically isolated and separated for long period of time, they may lose ability to interbreed and produce fertile offsprings. Thus leading to formation of new species

Genetic isolation exists when two populations are so different genetically that they cannot produce fertile offspring (or any offspring at all).
Temporal isolation is genetic isolation achieved due to temporal differences in breeding.
Behavioral

Isolation is a form of reproductive isolation in which two populations

have differences in courtship rituals or other types of behavior that

prevents them from interbreeding

The synthetic theory of evolution is based on gene mutation, gene recombination, natural selection, genetic drift, isolation.(Other factors-migration, hybridisation,chance)

1. Mutation, recombination, natural selection, genetic drift and isolation are involved in natural selection.
2. Mutation is an important source of variation that fulfills gene pool and remains a base to polygenic or multi-factorial inheritance.
3. The process of micro-evolution is governed by natural selection and gene flow is affected by reproductive isolation.
4. Evolution is governed by genetic drift.
5. Micro-evolutionary factors create new species.
   

Environmental variations are those variations which are merely due to environment. These variations are temporary and have nothing to do with the next generation. Hereditary variations are those variations which transfer to next generation. Discontinuous variations are sudden changes in organism which are also heritable.

• The author of the book Process of organic evolution was G.L. Stebbins. This book includes an explanation of the synthetic theory of evolution.
• The various concepts which are involved in the process of mutation and results in evolution.
• The phenomena like recombination, variation, isolation, etc. are considered and explained with respect to evolution. 

Evolution is the change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes that are passed on from parents to offspring during reproduction.

A subpopulation becomes reproductively isolated from its parental population. It is the formation of species without geographical isolation and these species are called sympatric speciation. It is reproductive, behavioural and temporal isolation.

The modern approach for understanding the organic evolution lays stress on subjects such as chromosomal aberrations, mutations, isolation, population. Hence, Option D is correct. 

The biological species concept defines species based on the ability of individuals to interbreed and produce fertile offspring, which is maintained by reproductive isolation from other groups.

Isolation, particularly reproductive or geographic, prevents gene flow between populations. This allows populations to diverge genetically, eventually leading to the formation of new species.

Malthus gave the theory of principal of population which proposes that the human population grows in geometric ratio while food materials increase in arithmetic proportion.

Synthetic theory is considered as Modern theory and the main contributor of this theory was G.L.Stebbins. They considered 5 factors, responsible for organic evolution. They are as follows

For understanding Evolution, we consider-

Reproductive isolation refers to the mechanisms that prevent two different populations from interbreeding and producing fertile offspring, which is a key step in speciation.

Reproductive isolation acts as a barrier that accelerates the divergence of gene pools, thereby hastening the process of speciation and organic evolution.

• Reproductive isolation refers to a set of mechanisms that prevent animals of the same group from breeding. These are reproductive barriers that do not allow the species to mate and produce offspring.
  
• Mule is an example of low hybrid viability type of reproductive isolation.
  
• Even though horses and donkeys can mate and produce healthy offspring, the offsprings thus produced termed mules cannot pass their genetic information down to future generations, so they are a genetic dead-end. There is no gene flow through infertile hybrids.
  

• Ecological isolation is a type of reproductive isolation in which mating is prevented because of the separation of species resulting from the difference in their habitat. 
  
• This usually occurs when the species are used to different habitat types, or different parts of the same habitat. Even if the geographic range of two species overlaps, the difference in their ecological needs and breeding requirements is enough to isolate them from each other.

• Reductions in population size and absence of gene flow can lead to reductions in genetic variability, reproductive fitness, and a limited ability to adapt to environmental change increasing the risk of extinction. 
  
• Island populations are typically small and isolated, and as a result, inbreeding and reduced genetic diversity elevate their extinction risk.
  

• The principle of Malthusian theory of human population states that human populations grow exponentially (i.e., doubling with each cycle) while food production grows at an arithmetic rate (i.e. by the repeated addition of a uniform increment in each uniform interval of time). 
  
• This scenario of arithmetic food growth with simultaneous geometric human population growth predicted a future when humans would have no resources to survive on. To avoid such a catastrophe, Malthus urged controls on population growth.
  

Creationism is the religious belief that the universe and life originated from specific acts of divine creation, as described in the theory of special creation.

Miller circulated four gases - methane, ammonia, hydrogen and water vapour in an air tight apparatus and passed electrical discharges from electrodes. He found a large number of simple organic compounds including some aminoacids such as alanine, glycine and aspartic acid. 

The mechanisms of reproductive isolation or hybridization barriers are a collection of mechanisms, behaviours and physiological processes, that prevent the members of two different species that cross or mate from producing offspring. These barriers maintain the integrity of a species over time, reducing or directly impeding gene flow between individuals of different species, allowing the conservation of each species characteristics. Cooperation helps in transmitting underlying genes to future generations either through increasing the reproductive successes of the individual (direct fitness) or of other individuals who carry the same genes (indirect fitness). 

Ethological isolation is defined as the failure of individuals of species with recent common ancestry (i.e., related species or semispecies) to produce hybrid offspring because differences in their behaviour prevent successful mating taking place.
The mallard or wild duck (Anas platyrhynchos) is a dabbling duck which breeds throughout the temperate and subtropical Americas, Europe, Asia, and North Africa, and has been introduced to New Zealand, Australia, Peru, Brazil, Uruguay, Argentina, Chile, the Falkland Islands and South Africa.
The pintail or northern pintail is a duck with wide geographic distribution that breeds in the northern areas of Europe, Asia and North America. It is migratory and winters south of its breeding range to the equator.
Ethological isolation stops their breeding in the natural habitats, whereas they breed in captivity.

In order for different species to diverge from common ancestors and drive evolution, reproductive isolation must occur. There are several types of reproductive isolation that lead to speciation. 

Heritable variations serve as raw material for natural selection and accumulation of selected heritable variations over generations leads to evolution. Diversification of ancestral line into different forms is referred to as adaptive radiation. Crossing over occurs during meiosis. Translocation is the step of elongation of peptide chain during translation. Cellular differentiation leads to tissue formation; meiosis is a type of cell division. Thus, the correct answer is option A.

Abnormal distributions to the gametes of whole chromosomes, chromosome segments or combinations of genes lead to hybrid sterility. Geographical, mechanical, temporal and behavioral isolations are pre zygotic barriers and prevent mating between groups by one or other means and hybrid is not produced. Thus, the correct answer is D.

The biogenetic law is a hypothesis of improvement and advancement proposed by Ernst Haeckel in Germany during the 1860s. It is one of a few summarization speculations, which set that the phases of advancement for a creature fetus are equivalent to other creatures' grown-up stages.

So, the correct option is 'Haeckel'.

Reproductive isolation prevents members of different species from producing offsprings or ensures that any offspring are sterile. These barriers maintain the integrity of a species by reducing gene flow between related species. So, the correct answer is "Reproductively isolated".

A) Darwin's characteristic choice is the procedure by which nature remunerates those people betters adjust to their surroundings with survival and regenerative achievement. It works at the dimension of qualities, areas of DNA that encode for proteins filled in as the product of life. 

B) The instrument of regenerative detachment is a gathering of developmental components, practices and physiological procedures basic for speculation. They keep individuals from various species from delivering posterity or guarantee that any posterity is sterile. 

C) Speciation is the developmental procedure by which populaces advanced to end ups particular species. 

D) Human Conversation is the intelligent correspondence between at least two individuals.

So, the correct option is 'Isolation'.

Thomas Malthus, in full Thomas Robert Malthus, (conceived February 13/14, 1766, Rookery, close Dorking, Surrey, England), English market analyst and demographer who is best known for his hypothesis that populace development will constantly will in general beat the sustenance supply.

A subpopulation becomes reproductively isolated from its parental population. It is the formation of species without geographical isolation and these species are called sympatric speciation.

According to Curvier, the Earth went through sudden changes, each of which could wipe out a number of species.  The causes may include asteroids, volcanoes, or relatively fast changes in sea level. These extinctions mark some of the great transitions in life when new groups of species got the opportunity to take over the niches of old ones.

From the biogenetic law or embryological parallelism often communicated utilizing Ernst Haeckel's expression "ontogeny restates phylogeny"is an authentic speculation that the advancement of the developing life of a creature, from preparation to incubation or bring forth (ontogeny), experiences stages taking after or speaking to progressive stages in the advancement of the creature's remote precursors (phylogeny).

So, the correct option is 'Ontogeny repeats phylogeny'.

The organism that is better adapted to the environment and hence, can produce more of its type is selected. Its population eventually grows and the other one is wiped out. Over long periods, this can even give rise to speciation i.e. formation of new species.