Organisms tend to increase the number of offsprings in the individual for survival in number. Then the interspecific, intraspecific, extra specific struggle for existence occurs. Then small changes occur from the parent generation to the next progenies which acts as a raw material for a source of evolution. And nature selects the useful or adaptive variation.

The main drawback of Darwinism is lack of knowledge of heredity. Darwin's theory could not explain the inheritance of variations from parents to offsprings through genes.

The theory of natural selection was proposed by Charles Darwin. It states that Natural selection is the process where organisms with favourable traits are more likely to reproduce. In doing so, they pass on these traits to the next generation. Over time this process allows organisms to adapt to their environment. Features which are necessary for evolution by natural selection to take place are 

1.  There is a struggle for existence, because of the disparity between the number of individuals produced by reproduction and the number that can survive.
   
2. Individuals within a species show variation; no two individuals are exactly alike. Those with advantageous characters have a greater probability of survival, and therefore of reproducing, in the struggle for existence.
   
3. Individuals produce offspring that tend to resemble their parents (the principle of inheritance). Provided that the advantageous characters that promote survival are inherited by offspring.
   
4. The offspring that evolve according to the condition are fittest for survival.
5. Those are selected by nature and weaker ones got eliminated.

• Darwinism is an evolutionary theory proposed by Charles Robert Darwin, an English Naturalist. He believed that evolution is a gradual, rather than a sudden biological event. His theory was based on several facts, He sailed round in Beagle, his ship observations and inferences. They are 1) overproduction, 2) constancy in population, 3) struggle for existence, 4) natural selection.
  
• The prodigality of production or overproduction: Every organism tends to increase its population in large proportions. For example, Paramecium divides by binary fission at the rate of three to four times a day. At this rate, the volume of all the paramecia equals to 10,000 times that of the earth at the end of the 9000th generation in the absence of any check.
• Constancy in population: However, such an abnormal increase is not noticed in the population of any species in nature as the offspring die in large number before reaching the reproductive age. It is true that the food and the other sources do not increase in the same proportion as that of the population.
• Struggle for existence: As the food sources are limited, severe competition exists among the members of a population. Darwin called it a struggle for existence.
• Natural selection: The organisms with less reproductive success are not represented in future generations, however, fit they may be in the struggle for existence. This is called the Natural selection. Herbert Spencer called this phenomenon Survival of the fittest.
• Darwinism failed to explain the mechanism by which variations occur. Thus Darwin faced the criticism "DARWINISM EXPLAINS THE SURVIVAL OF THE FITTEST BUT NOT THE ARRIVAL OF THE FITTEST".

• Darwinism is an evolutionary theory proposed by Charles Robert Darwin, an English Naturalist. He believed that evolution is a gradual, rather than a sudden biological event. His theory was based on several facts, observations and inferences. They are 

• The prodigality of production or overproduction: Every organism tends to increase its population in large proportions. For example, Paramecium divides by binary fission at the rate of three to four times a day. At this rate, the volume of all the paramecia equals to 10,000 times that of the earth at the end of the 9000th generation in the absence of any check.
• Constancy in population: However, such an abnormal increase is not noticed in the population of any species in nature as the offspring die in large number before reaching the reproductive age. It is true that the food and the other sources do not increase in the same proportion as that of the population.
• Struggle for existence: As the food sources are limited, severe competition exists among the members of a population. Darwin called it a struggle for existence.
• Natural selection: The organisms with less reproductive success are not represented in future generations, however, fit they may be in the struggle for existence. This is called the Natural selection. Herbert Spencer called this phenomenon Survival of the fittest.
• He wrote Origin of Species including these points in 1859.

• The law of independent assortment was given by Mendel. He also gave the 'Law of Dominance' and 'Principle of Segregation'.

The Darwin theory of natural selection can be concluded as :

Darwin's theory of natural selection explains organic evolution as follows : 

• The human population increases exponentially when the resources are unlimited according to Darwin.
• Unlimited resources are the ones that increases arithmetically.

In 1859, Charles Darwin in his book 'Origin of species' stated the 'theory of evolution'. in this theory he has stated that no two individuals are the same but they have variations which help them in survival. This is called a natural selection. According to his theory, evolution is a slow and continuous process as it creates variation among individuals, these variations may or may not be passed among the offsprings. He had not explained the population growth and the phylogeny of an individual.

Darwin developed a theory of biological evolution in which by observing a different type of finches in the Galapagos islands. He observed 15 species of passerine birds and they varied island to island. This observation helped him to give a theory on natural selection and that lead to evolution to Finch species. 

Charles Darwin was influenced by Thomas Robert Malthus, a late-eighteenth century economist. Malthus wrote "Essay on the Principle of Population" (1798), which Darwin read and was inspired by. The central theme of Malthus' work was that population growth would always overpower food supply growth, creating perpetual states of hunger, disease and struggle. The natural, ever-present struggle for survival caught the attention of Darwin and he extended Malthus' principle to the evolutionary scheme. 

Charles Darwin went on a trip aboard HMS beagle as a naturalist. The purpose of this voyage was to map the uncharted areas of south Americal coastline. Darwin observed unique species of plants and animals in South America like finches and iguana. He noticed that the temperate South American animals closely resembled the tropical South Americal animals as compared to temperate European animals. Some of the characteristics of fossils observed by him in South America were similar with the contemporary South American characters of organisms.

The Descent of Man and Selection in Relation to Sex is a book by English naturalist Charles Darwin, first published in 1871, which applies evolutionary theory to human evolution, and details his theory of sexual selection, a form of biological adaptation distinct from, yet interconnected with, natural selection. The book discusses many related issues, including evolutionary psychology, evolutionary ethics, differences between human races, differences between sexes, the dominant role of women in mate choice, and the relevance of the evolutionary theory to society. Thus, option A is correct.

Darwin proposed the theory of natural selection to explain the process of evolution. According to Darwin’s theory of natural selection, all organisms have the potential to reproduce limitlessly irrespective of the fact that each species maintain a constant density over time. However, the struggle for existence, i.e. the competition among individuals for available resources to survive and reproduce, put a check on species density and maintains it at a constant level. Survival of fittest is unequal ability of individuals to survive and reproduce based on suitability of their inherited characters to prevailing environmental conditions. It imparts the reproductive advantage to certain organisms which account for major part of the gene pool of the species. Thus, natural selection favors the individual with survival and/or reproductive advantage over others under existing environmental condition. Thus, the correct answer is option D.

Charles Darwin visited Galapagos islands, the chain of 22 islands located in the Pacific Ocean on the west coast of South America, during his voyage on HMS Beagle. Since Galapagos islands were once connected with South America mainland, many birds of the island resembled those of mainland. This observation laid the foundation of his concept of adaptive radiation and his theory of evolution. Thus, the correct answer is option B.

Darwin proposed the theory of natural selection to explain the process of evolution which was published in the book entitled The Origin of Species by Means of Natural Selection, 1859. Linnaeus is considered as the father of taxonomy and was first to use the binomial nomenclature for organisms in his book “Species Plantarum, 1753” in which he gave a generic name to each species. Philosophie Zoologique was published by Lamarck in 1809 in which he proposed his theory of evolution, Lamarckism.Thus, the correct answer is option A.

Charles Darwin came up with the idea of evolution of species with natural selection. Therefore, (c) is the correct answer.

Speciation is the term used for the development of new species by changes in population. Charles Darwin was the first to describe role of natural selection in speciation. Therefore, (b) is the correct answer.

Charles Darwin was born in year 1809. His bicentenary year was 2009.

British naturalist Alfred Russel Wallace worked on a diversity of plants and animals of Malay Archipelago, reached at the same conclusion as Darwin. Wallace's book, "Contributions to the Theory of Natural Selection", was published in 1870.

'Descent of man' was another publication by Darwin after he published 'Origin of species' in 1859.

Phyletic evolution actually refers to slow gradual evolution. It is a theory stating that, evolutionary change happens slowly, steadily and gradually in an attempt of the species to continue to adapt to changes in the environment, until they gradually become new species.

• Charles Darwin proposed the theory of natural selection. It emphasized that in a population, variations result based on different combinations of traits and the carrying capacity of the environment is limited. 
• Hence there cannot be a guarantee of breeding and reproduction probability. In such a situation nature selects the best-adapted organisms for survival with better traits than the other.  
• Such an organism will have a greater chance of becoming parents for the next generation because of its superior characters. 
• So there is a struggle among the organisms for existence in which only the fittest organism survives and others perish. This concept is called as the survival of the fittest. Thus the correct answer is option C. 

Darwin notes that there is greater variation observed in domesticated species than would be seen in the wild. Darwin admits that the laws governing inheritance are not yet fully understood, why some traits might skip generations while others only appear in one sex or the other. He reviews a number of domesticated species, in particular various breeds of dogs where it remains unclear if they derive from a single parent species or several. After the different types of animals he has focused his study on domestic pigeons. So, the correct answer is "Breeding domesticated animals".

Darwin in his old ages returned to earthworms and wrote a book which described the volume of soil that earthworms swallow and eject as castings. He reported that an acre of land may contain about 50,000 earthworms and yield 18 tons of castings per year. So, the correct answer is 'About 50,000 earthworms'.

• The Galapagos Islands are located in the eastern Pacific Ocean, 973 km off the west coast of South America.
• Galapagos islands discovered in 1535 by a Spanish bishop named Fray Tomas de Berlanga, he named the island Galapagos after the impressive giant tortoises found there.
• Hence the name Galapagos islands have been given on the basis of occurrence of Giant Tortoises.
  
• So, the correct answer is 'Giant Tortoises'.

• The term Darwin's finches was given to Galapagos finches because, On his visit to the Galapagos Islands, Charles Darwin discovered several species of finches that varied from island to island, which helped him to develop his theory of natural selection.
• Darwin's finches comprise a group of 15 species endemic to the Galápagos (14 species) and Cocos (1 species) Islands in the Pacific Ocean.
• The term Darwin's finches was given to Galapagos finches by David Lank in the book Darwin's finches.
  
• So, the correct answer is 'Lank'.

• The term Darwin's finches was given to Galapagos finches because, On his visit to the Galapagos Islands, Charles Darwin discovered several species of finches that varied from island to island, which helped him to develop his theory of natural selection.
• Darwin's finches comprise a group of 15 species endemic to the Galápagos (14 species) and Cocos (1 species) Islands in the Pacific Ocean.
• Hence Darwin's finches occur in Galapagos islands.
• So, the correct answer is 'Galapagos islands'.

The Galapagos Islands were prominently featured in Charles Darwin's landmark book on evolution, The Origin of  Species. On his visit to the Galapagos Islands, Charles Darwin discovered several species of finches that varied from island to island, which helped him to develop his theory of natural selection.

Thomas Malthus' work helped inspire Darwin to refine the natural selection by stating a reason for meaningful competition between members of the same species. Not surprisingly, Malthus, an ordained minister, believed that hunger and disease were aspects of life implemented by God to stop populations from exploding. Malthus was an influence through his book 'Essay on Population'

So, the correct answer is 'Origin of Species'

On the Origin of Species (or, more completely, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life), published on 24 November 1859, is a work of scientific literature by Charles Darwin which is considered to be the foundation of evolutionary biology.

The most important theory of general biology is the theory of evolution by natural selection. In the early 19th century Jean-Baptiste Lamarck (1744 – 1829) proposed his theory of the transmutation of species, the first fully formed theory of evolution. In 1858 Charles Darwin and Alfred Russel Wallace published a new evolutionary theory, explained in detail in Darwin's On the Origin of Species (1859).

The main concept of Darwin's theory was natural selection. Other main points were High rate of reproduction, Total number almost constant, Struggle for existence, Variations, Survival of the fittest. It didn't had genetic drift. Hence, option C is correct.

In 1868, Darwin put forward the Theory of Pangenesis. According to this theory, every organ of the body produces minute hereditary particles, called gemmules or Pangenes, and they can be carried through the blood into the gametes. It laid emphasis on some basis of inheritance. Hence, Option A is correct. 

The main features of Darwin's theory of Natural Selection are as follows - 

One of the major drawbacks of Darwin's theory is the absence of knowledge on inheritance. The genetic basis of evolution, cause of variations was not included in Darwin's 'Origin of Species'. It was only after the discovery of genes and traits by Mendel, genetics could be associated with evolution.

The small black birds found on Galapagos islands, which later came to be known as Darwin's finches were originally adapted with seed-eating features. From these many other forms evolved with altered beaks depending on the food habit. This enabled them to become insectivorous and vegetarian finches.

• Darwin reached the Galapagos islands on HMS Beage while travelling which is of historic importance.
  
• During his visit to the islands, Darwin noted that the unique creatures were similar from island to island, but perfectly adapted to their environments which led him to ponder the origin of the islands' inhabitants.
  
• So, Darwin's visit to the Galapagos Islands had a resounding impact on the formation of his Theory of Natural Selection.
  

Darwin's Theory of Evolution states that groups of organisms will undergo genetic changes over time due to the process of natural selection. If enough changes occur, this can create new species from the pre-existing ones. Variations in a species' genetics that lead to evolution often come from mutations.

According to Darwin the evolution occurs due to adaptation of the species to the environmental conditions , these adaptations are then carried out to the next generation by reproduction thus the species survive and evolve 

The Charles Darwin's theory is based on the survival of the fittest , the species who readily adapt to the changes in the environment for its existence tend to live. The species fitting to the natural selection only survive

Darwin concluded that organisms reproduce prolifically and in each generation the number of individual increases that can survive. The individuals show some phenotypic variations, and these variations are heritable. Darwin also suggested that the process of evolution is based on natural selection.

On his visit to the Galapagos Islands, Charles Darwin found a few types of finches that fluctuated from island to island, which helped him to build up his hypothesis of characteristic selection. Darwin's finches are a traditional case of a versatile radiation. Their regular precursor touched base on the Galapagos around two million years prior. Amid the time that has passed Darwin's finches have advanced into 15 perceived species contrasting in body measure, snout shape, melody and sustaining conduct.

The key aspects of the theory of natural selection are rapid increase in population, struggle for existence resulting from limited food and space, Natural selection or survival of the fittest and elimination of the unfit and origin of new species. Darwinism fails to attribute the reasons for the existence of vestigial organs like vermiform appendix in human beings. These organs should have been eliminated during the progression of evolution because of its no use for long time. Another big limitation is the difference between heritable and non-heritable variations. Theory of natural selection fails to explain the origin of variation. Further, Darwin believed evolution is due to gradual variations. But in many instances, the occurrence of such variations are not of use for the struggle of existence. For example, the eye in the case of animals is functional only in a fully formed condition and all the features of the eye according to Darwin could not have come into existence at one step. It should have been by the collection of several mutations. But then each change by itself is of no advantage. Thus, the correct answer is 'All of the above.'

One of his persuasions was Thomas Robert Malthus, a late-eighteenth-century financial analyst. Malthus stated is "Essay on the Principle of Population" (1798), which Darwin read and was roused.

According to Darwin theory, there is both long and short neck giraffe due variation in the population. when there is a shortage of short tree leaves, short neck giraffe died and long neck giraffe survive.