Mechanism of Evolution Questions in English

(C) Evolution by anthropogenic action refers to changes in organisms due to human activities.
$(b)$ Herbicide-resistant weeds: These evolve due to the excessive use of herbicides.
$(c)$ Drug-resistant eukaryotes: These evolve due to the misuse or overuse of medicines/antibiotics.
$(d)$ Man-created domesticated breeds like dogs: These are the result of artificial selection performed by humans.
$(a)$ Darwin's finches on the Galapagos Islands are an example of natural selection (adaptive radiation),not anthropogenic action.
Therefore,$(b), (c),$ and $(d)$ are correct examples.

(N/A) Charles Darwin conducted a sea voyage around the world between $1831-1836$ on the ship $HMS$ Beagle.
During this period,Darwin explored the flora and fauna of various continents and islands.
Based on his observations,he concluded the following: $(i)$ There has been a gradual evolution of life forms,with new forms arising at different periods in Earth's history. $(ii)$ Varying degrees of similarities exist between existing life forms and those that lived millions of years ago. $(iii)$ Populations of all organisms possess variations in characteristics,which help them adapt better to their environment. Characteristics that enable some individuals to survive better in natural conditions (food,climate,physical factors) allow them to outbreed others (survival of the fittest).
Thus,fitness,according to Darwin,refers ultimately to reproductive fitness.
Such fit individuals leave more progeny than others.
Consequently,organisms that are better adapted will survive more in nature and be selected by nature. This is called natural selection.
Branching descent (e.g.,Darwin's finches) and natural selection are the two key concepts of the Darwinian theory of evolution.
Alfred Wallace,a naturalist who worked in the Malay Archipelago,reached similar conclusions to Darwin.
Thus,they both jointly proposed the theory of 'Natural Selection' in $1858$.
It is based on the following factual observations: $(a)$ Natural resources are limited. $(b)$ Population sizes are stable except for seasonal fluctuations. $(c)$ Members of a population possess varying characteristics; no two members are identical,even if they appear superficially similar. $(d)$ Variations are generally inherited. $(e)$ Population size involves two facts: theoretically,it grows exponentially if everyone reproduces maximally,but in reality,population size is limited due to competition among individuals for resources.
Those that are better adapted survive and reproduce at the expense of those that are less adapted to the environment.

(N/A) In $1901$,Hugo de Vries carried out experiments on the evening primrose plant ($Oenothera$ $lamarckiana$) and proposed the mutation theory of evolution.
This theory states that evolution occurs due to sudden,large differences (mutations) in a population.
He believed that mutation is the primary cause of evolution,rather than the minor heritable variations that Darwin discussed.
Mutations are random and directionless,whereas Darwinian variations are small and directional.
For Darwin,evolution was a gradual process,while de Vries believed that mutation caused speciation,which he termed as saltation (single-step large mutation).
Later studies in population genetics provided further clarity on these mechanisms.

(N/A)

Properties	Lamarckism,Darwinism,and Mutation Theory Comparison
$(a)$ Vital force	Lamarckism believes in an internal vital force for size increase. Darwinism and Mutation Theory do not believe in any internal vital force.
$(b)$ Conscious Reaction	Lamarckism suggests animals react consciously to environmental changes. Darwinism and Mutation Theory do not involve conscious reactions in evolution.
$(c)$ Appetency	Lamarckism considers desires (appetency) as a force for modification. Darwinism and Mutation Theory do not consider appetency as a factor.
$(d)$ Use and disuse	Lamarckism emphasizes the use and disuse of organs. Darwinism and Mutation Theory are silent regarding the use and disuse of organs.

(N/A) In a large population,the effect of chance events on allele frequencies is negligible because the large number of individuals buffers against random fluctuations.
However,in a small population,the number of individuals carrying a specific allele is low.
Therefore,random chance events (such as accidents,natural disasters,or sampling errors) can significantly increase,decrease,or even completely eliminate certain alleles from the gene pool,leading to a rapid change in allele frequencies.

(N/A) $Genetic \ drift$ refers to the random change in allele frequencies in a population due to chance events,independent of whether the traits are useful or harmful. This often occurs when a small section of a population is isolated,migrates,or dies due to a natural calamity,leading to a shift in the genetic makeup of the remaining population.
$Gene \ migration$ $(Gene \ flow)$ occurs when individuals from one population migrate into another and interbreed with the members of the local population. This process introduces new alleles into the local gene pool of the host population,thereby altering the allele frequencies.

(N/A) Saltation refers to single-step large mutations that lead to speciation and evolution. This concept was proposed by Hugo de Vries,who believed that evolution is caused by sudden,large,and heritable changes (mutations) in a population,rather than small,directional variations as proposed by Darwin.

(B) According to $Darwin$,fitness is ultimately based on the ability of an organism to survive and reproduce in its environment.
$Darwinian$ fitness is defined as the relative ability of an organism to pass on its genes to the next generation.
Therefore,it is referred to as reproductive fitness,as those who are more fit leave more offspring.

(B) Before industrialization in England (around the $1850$s),the tree trunks were covered with white-colored lichens.
In this environment,the white-winged moths (Biston betularia) were better camouflaged against predators compared to the dark-winged (melanized) moths.
Therefore,the population of white-winged moths was significantly higher than that of the dark-winged moths.
This is a classic example of natural selection.

(C) In England,before industrialization in the $1850$s,there were more white-winged moths on trees than dark-winged (melanized) moths because the white lichens on tree trunks provided camouflage for the white-winged moths.
After industrialization,the tree trunks became dark due to smoke and soot,which killed the lichens.
This change favored the dark-winged (melanized) moths as they could hide better against the soot-covered bark,while the white-winged moths were easily spotted and eaten by predators.
By the $1920$s,the population of melanized moths had significantly increased compared to the white-winged variety due to this selective advantage.

(A) In the case of industrial melanism,before industrialization,the tree trunks were covered with white-colored lichens. The white-winged moths were able to camouflage against these lichens,making them less visible to predators. However,after industrialization,the tree trunks became dark due to soot and smoke,and lichens died. This created a 'contrasting background' for the light-colored moths,making them easily visible and identifiable to predators,while the dark-colored (melanic) moths were better camouflaged.

(B) The survival of moths, specifically the peppered moth $(Biston \text{ betularia})$, is a classic example of natural selection. Before industrialization, light-colored moths were better camouflaged against light-colored lichens on tree trunks. After industrialization, soot darkened the trees, making dark-colored moths better camouflaged against predators. This process of blending into the environment to avoid predation is known as camouflage.

(C) The excessive use of herbicides and pesticides creates a strong selective pressure on populations of weeds and insects.
Individuals that possess natural genetic variations conferring resistance to these chemicals survive and reproduce.
Over a short period,these resistant individuals pass on their genes to the next generation,leading to the rapid selection of resistant varieties.
This is a classic example of anthropogenic action leading to evolution by natural selection.

(C) The core essence of Darwinism, as proposed by Charles Darwin, is the theory of $Natural \text{ } selection$.
According to this theory, individuals with traits better suited to their environment are more likely to survive and reproduce, passing these advantageous traits to the next generation.
This process leads to the gradual adaptation and evolution of populations over time.

(A) The rate of appearance of new forms (evolutionary change) is directly proportional to the generation time and the frequency of reproduction.
$E. coli$ is a bacterium with a very short generation time (approximately $20$ minutes).
Because bacteria reproduce rapidly and have a high mutation rate per generation,they can evolve and show new forms much faster than complex multicellular organisms like fish,humans,or pangolins.
Therefore,$E. coli$ exhibits the highest rate of appearance of new forms among the given options.

(D) Natural selection,as proposed by Charles Darwin,is primarily based on observable facts and phenomena in nature.
$1$. Darwin observed that individuals within a population exhibit variations.
$2$. He noted that resources are limited,leading to a struggle for existence.
$3$. Individuals with advantageous variations are more likely to survive and reproduce,a process known as differential reproduction.
$4$. These observations of natural phenomena form the foundation of the theory of natural selection.

(D) Charles Darwin,in his theory of natural selection,proposed that individuals with heritable variations that allow for better resource utilization are more likely to survive and reproduce. This process leads to these individuals leaving more progeny in the next generation,which is the core mechanism of natural selection.

(B) Hugo de Vries proposed the mutation theory based on his work on the evening primrose $(Oenothera \, lamarckiana)$.
He believed that evolution is a saltatory process, meaning it occurs through large, sudden, and heritable variations called mutations.
Unlike Darwin's theory of gradual accumulation of small variations, de Vries emphasized that mutations are the primary cause of evolution.

(C) According to Hugo de Vries,evolution is caused by sudden large mutations,which he called saltation (single-step large mutation).
While natural selection and recombination contribute to gradual changes,sudden and significant changes in the genetic makeup of a population are attributed to mutations.

(B) Charles Darwin,in his theory of natural selection,proposed that variations within a population are small and directional. He believed that these small,heritable variations accumulate over generations,leading to evolutionary change in a specific direction favored by natural selection. In contrast,Hugo de Vries proposed that mutations (variations) are large,random,and directionless.

(A) Saltation is a term coined by Hugo de Vries to describe the mechanism of evolution through large,sudden,and discontinuous variations.
These variations are known as mutations.
Unlike Darwin's theory of gradual evolution,saltation suggests that new species arise from a single step of large mutation.
Therefore,saltation refers to a single step large mutation.

(C) The term $Saltation$ refers to single-step large mutations.
$Hugo \ de \ Vries$ proposed the mutation theory of evolution based on his work on the evening primrose $(Oenothera \ lamarckiana)$.
He believed that evolution is a discontinuous process caused by large,sudden mutations,which he termed $Saltation$.

(A) When migration of a section of population to another place and population occurs,gene frequencies change in the original as well as in the new population. New genes/alleles are added to the new population and these are lost from the old population. There would be gene flow if this gene migration happens multiple times. If the same change occurs by chance,it is called genetic drift.

(A) Gene flow refers to the movement of alleles or genes from one population to another.
When individuals migrate from one population to another,they carry their alleles with them.
As a result,these alleles are added to the gene pool of the new population and are simultaneously removed from the gene pool of the original (old) population.
This process changes the allele frequencies in both populations,thereby affecting the genetic equilibrium.

(C) The founder effect occurs when a small group of individuals breaks off from a larger population to establish a new colony.
Because the new population is small,the allele frequencies in the new group may differ significantly from the original population due to random sampling error.
This phenomenon is a specific type of genetic drift,where the change in allele frequency is due to chance events in a small population.
Therefore,the founder effect is associated with genetic drift in a small founder population.

(B) The incorrect statement is that mutations are small and directional. According to Hugo de Vries, mutations are large, sudden, and random (non-directional) changes in the genetic material. In contrast, Darwinian variations are small and directional, leading to gradual evolution. Hugo de Vries's work on evening primrose $(Oenothera \text{ lamarckiana})$ led to the Mutation Theory, which emphasizes that evolution is a saltatory (discontinuous) process, not a gradual one.

(C) The provided figure shows a population distribution where the extreme phenotypes are favored over the intermediate phenotype,leading to the formation of two peaks.
This type of natural selection is known as disruptive selection.
In disruptive selection,the intermediate phenotype is selected against,while both extremes are favored,resulting in a bimodal distribution curve.

(D) Genetic drift refers to the random fluctuations in allele frequencies in a population over generations due to chance events.
It is named after the American biologist Sewall Wright,who extensively studied and described this phenomenon.
Therefore,genetic drift is also known as the $Sewall \ Wright \ effect$.

(A) Adaptation is the evolutionary process whereby an organism becomes better suited to its habitat. It involves morphological,physiological,or behavioral changes that allow an organism to survive and reproduce in its environment. These adaptations are genetically fixed over generations,thereby contributing to the genetic stability of the population in a specific environment. While migration and regulation are strategies used by organisms to cope with environmental changes,adaptation is the fundamental characteristic that ensures long-term survival and evolutionary success.

(A) Biological evolution is significantly influenced by interactions between species. Among the given options, $Competition$ (specifically $Interspecific \text{ } competition$) is considered a potent force in evolution. It drives natural selection by forcing species to adapt, specialize, or occupy different niches to avoid extinction, thereby leading to evolutionary divergence and the development of new traits.

(D) Industrial melanism is an adaptation where the moths living in industrial areas developed melanin pigments to match their body to the black soot (smoke) covered surroundings.
Before industrialisation, the light-coloured moths were well-camouflaged against the whitish lichens on tree barks, making them less visible to predatory birds.
After industrialisation, the tree barks became covered with black soot, making the light-coloured moths highly visible and easily preyed upon by birds.
Conversely, the dark-coloured (melanic) moths were better camouflaged against the soot-covered barks, allowing them to survive and reproduce.
This process, where the environment selects for the better-adapted phenotype, is a classic example of natural selection.

(B) Harmful mutations are not eliminated from the gene pool primarily because most of them are recessive.
In a diploid population,these recessive alleles are masked in the heterozygous state $(Aa)$,where the dominant allele $(A)$ expresses the normal phenotype,thus protecting the individual from the harmful effects of the recessive mutation $(a)$.
Since the mutation is not expressed in the phenotype of the heterozygote,it is not subjected to natural selection,allowing it to persist in the gene pool.
Statements $I$,$II$,and $IV$ do not explain the persistence of harmful recessive mutations in the gene pool. Therefore,$I$ and $II$ are incorrect explanations.

(A) The concept that 'population tends to increase geometrically,while food supply increases arithmetically' was proposed by $TR$ Malthus. This observation significantly influenced Charles Darwin's theory of natural selection,as it highlights the struggle for existence due to limited resources.

(A) The correct answer is Directional evolution.
Natural selection processes are categorized as follows:
$(i)$ Stabilizing Selection (Balancing selection): This type of selection favors average-sized individuals while eliminating small and large-sized individuals. It reduces variation and does not promote evolutionary changes. It maintains the mean value from generation to generation. The graphical curve of the population remains bell-shaped.
$(ii)$ Directional Selection (Progressive selection): In this selection,the population changes towards one particular direction. This type of selection favors either small or large-sized individuals,and more individuals of that type will be present in the new generation. The mean size of the population shifts.
$(iii)$ Disruptive Selection (Diversifying selection): This type of selection favors both small-sized and large-sized individuals. It eliminates most of the members with mean expression,producing two peaks in the distribution of the trait,which may lead to the development of two different populations. This kind of selection is the opposite of stabilizing selection and is rare in nature but is very important in bringing about evolutionary changes.

(D) Hugo de Vries conducted his experiments on $Oenothera$ $lamarckiana$ (Evening primrose).
He observed that when the plant was self-pollinated and its seeds were allowed to grow, the majority of $F_1$ plants were similar to the parents, but a few were significantly different.
Based on these experiments, Hugo de Vries proposed the Mutation Theory, suggesting that new types of inherited characters may appear suddenly without any previous indication of their presence in the population.

(A) Saltation refers to a single-step large mutation.
Hugo de Vries proposed that evolution is caused by large,sudden mutations rather than the minor,heritable variations suggested by Darwin.
Mutations are random and directionless,whereas Darwinian variations are small and directional.
The term 'saltation' specifically describes these single-step large mutations,which can lead to the formation of new species.

(A) The phenomenon described is the $Founder \text{ effect}$.
When a small group of individuals from a larger population migrates to a new, isolated geographical area, the allele frequencies in this new group may differ significantly from the original population due to genetic drift.
These original individuals are referred to as $founders$, and the resulting change in the genetic makeup of the new population is known as the $Founder \text{ effect}$.
Over time, this can lead to the formation of a distinct species.

(A) Sewall Green Wright was an American geneticist known for his influential work on evolutionary theory.
The theory of random genetic drift was proposed by him.
Genetic drift or allelic drift is the change in the frequency of a gene variant (allele) in a population due to random sampling.
The effect of genetic drift is larger in small populations and smaller in large populations.

(C) The phenomenon of industrial melanism is a classic example of natural selection. In $19^{th}$ century England,before industrialization,white-winged moths were more abundant than dark-winged moths because they were camouflaged against light-colored lichens on tree trunks. After industrialization,soot covered the trees,making the dark-winged moths better adapted to survive predation by birds. This differential survival and reproduction based on environmental changes is the essence of natural selection.

(C) Herbert Spencer $(1820-1903)$ coined the phrase 'survival of the fittest' to describe the mechanism of natural selection.
According to this concept,in the struggle for existence,only those individuals survive that possess the most advantageous variations.
While Charles Darwin popularized the theory of natural selection,the specific terminology 'survival of the fittest' was introduced by Herbert Spencer.

(C) Darwin's theory of evolution,known as the theory of natural selection,proposes that individuals with traits better suited to their environment are more likely to survive and reproduce. Over generations,this process of natural selection leads to the accumulation of favorable variations,resulting in the divergence and differences observed between species.

(C) Hugo de Vries $(1901)$ proposed the mutation theory of evolution.
This theory states that evolution is a jerky and discontinuous process where new species arise suddenly due to large,heritable mutations,which act as the raw material for evolution.

(C) Industrial melanism is a term used to describe the evolutionary process in which darker individuals come to predominate over lighter individuals as a result of natural selection following the industrial revolution.
Before $1848$,almost every individual of the peppered moth ($Biston$ $betularia$) captured in Great Britain had light-coloured wings with black specklings.
In $1848$,a black form of the moth was recorded in Manchester,and by $1895$,$98\%$ of the peppered moth population in Manchester was black.
This black melanic form arose due to a recurring random mutation,which provided a survival advantage in soot-covered environments.

(B) In $1831$,Charles Darwin accepted an unpaid post of naturalist on the survey ship $HMS$ Beagle,which spent five years at sea charting the east coast of South America,leading him to develop the theory of natural selection.
Alfred Russell Wallace had travelled widely in South America,Malaya,and the Eastern Indian archipelago and arrived at the same conclusions as Darwin regarding natural selection.
In $1858$,Wallace wrote an essay outlining his theory and sent it to Darwin. This stimulated Darwin,and in July $1858$,both presented papers on their ideas at a meeting of the Linnean Society in London.
Subsequently,in $1859$,Darwin published his landmark book,'On the Origin of Species by Means of Natural Selection'.

(D) Evolutionary changes are based on variations that are heritable and can be passed on to the next generation.
Differences arising from diet,health,age,or accidents are somatic (acquired) variations.
These changes do not affect the organism's genetic material $(DNA)$.
Therefore,they are not transmitted to offspring and are not significant from an evolutionary standpoint.

(B) Geographic speciation (allopatric speciation) follows this sequence:
$1$. Geographic barrier: $A$ physical barrier separates a population into two groups.
$2$. Genetic divergence: Due to different environmental pressures and mutations,the two groups accumulate genetic differences over time.
$3$. Reproductive isolation: Eventually,the genetic differences become so significant that the two groups can no longer interbreed,leading to the formation of new species.
Thus,the correct sequence is: Geographic barrier $\rightarrow$ Genetic divergence $\rightarrow$ Reproductive isolation.

(C) Natural selection is a process where organisms better adapted to their environment tend to survive and produce more offspring.
This reproductive success leads to the passing on of advantageous traits to the next generation.
Therefore,the most accurate description of natural selection is the reproductive success of the members of a population that are best adapted to their environment.

(B) The two key concepts of Darwinism are Branching Descent and Natural Selection.
$1.$ Branching Descent: Darwin proposed that all life forms share common ancestry,and evolution occurs through the branching of lineages.
$2.$ Natural Selection: This is the mechanism by which organisms better adapted to their environment tend to survive and produce more offspring.
$I$ and $II$ (Use and disuse of organs,Inheritance of acquired characters) are associated with Lamarckism.
$V$ (Mutation) is associated with Hugo de Vries' Mutation Theory.
$VI$ (Reproductive isolation) is a key concept of the Modern Synthetic Theory of evolution.

(C) According to Darwin,fitness is ultimately defined by reproductive success.
Darwin realized that in a population facing intense competition,variations that favor survival in a specific environment increase an individual's ability to reproduce and leave fertile offspring.
Individuals with favorable variations are more likely to survive and pass their traits to the next generation.
Therefore,the 'survival of the fittest' is essentially the selection and proliferation of organisms that are most suitably adapted to their environment,measured by their contribution to the gene pool of the next generation,i.e.,the number of offspring produced.