Chapter 14: Evolution

Select the correct answer:1. Lamarck theory of organic evolution is usually known as

A) Natural selection

B) Inheritance of acquired characters

C) Descent with change

D) Survival of the fittest

Answer: B) Inheritance of acquired characters

Explanation: Lamarck proposed that organisms can pass on traits acquired during their lifetime to their offspring, a concept known as the inheritance of acquired characteristics.

2. According to Neo-Darwinism, natural selection operates through

A) Fighting between organisms

B) Variations

C) Killing weaker organism

D) Differential reproduction

Answer: D) Differential reproduction

Explanation: Neo-Darwinism combines Darwin's theory with genetics. It emphasizes that natural selection acts through differential reproduction, where individuals with favorable variations produce more offspring.

3. The bones of forelimbs of whale, bat, horse and man are similar in structure, because

A) one organism has given rise to another

B) they share a common ancestor

C) they perform the same function

D) they have the biochemical similarities.

Answer: B) they share a common ancestor

Explanation: These are homologous structures, meaning they have the same underlying anatomical structure inherited from a common ancestor, despite being adapted for different functions.

4. Fitness according to Darwin refers to

A) number of species in a community

B) useful variation in population

C) strength of an individual

D) reproductive fitness of an organism.

Answer: D) reproductive fitness of an organism.

Explanation: In evolutionary terms, fitness is measured by an organism's ability to survive and reproduce, passing its genes to the next generation.

5. Analogous organs arise due to;

A) divergent evolution

B) artificial selection

C) genetic drift

D) convergent evolution.

Answer: D) convergent evolution.

Explanation: Analogous organs are structures that perform similar functions but have different evolutionary origins. They arise due to convergent evolution, where unrelated species adapt to similar environments.

6. First life form on earth was a

A) cyanobacterium

B) heterotroph

C) autotroph

D) photoautotroph.

Answer: B) heterotroph

Explanation: The first life forms are believed to have been heterotrophs, obtaining energy and nutrients from the organic molecules present in the primordial soup.

7. Which of the following statements is true?

A) Wings to birds and insects are homologous organs.

B) Human hands and wing of bat are analogous organs.

C) Wing of butterfly and wing of bat are homologous organs.

D) Flipper of penguin and dolphin are analogous organs.

Answer: D) Flipper of penguin and dolphin are analogous organs.

Explanation: The flippers of penguins (birds) and dolphins (mammals) perform the same function (swimming) but have different evolutionary origins, making them analogous.

8. Which one of the following phenomena supports Darwin's concept of natural selection in organic evolution?

A) Development of transgenic animals

B) Production of 'Dolly', the sheep by cloning

C) Prevalence of pesticide resistant insects

D) Development of organs from 'stem cells' for organ transplantation.

Answer: C) Prevalence of pesticide resistant insects

Explanation: The development of pesticide resistance in insects is a classic example of natural selection. Insects with genetic variations that confer resistance survive and reproduce, passing on the trait.

9. By the statement 'survival of the fittest', Darwin meant that

A) the strongest of all species survives

B) the most intelligent of the species survives

C) the cleverest of the species survives

D) the species most adaptable to changes survives.

Answer: D) the species most adaptable to changes survives.

Explanation: "Fitness" in Darwinian terms refers to reproductive success, which is often linked to an organism's ability to adapt to its environment.

10. According to Lamarckism, long necked giraffes evolved because

A) nature selected only long necked ones

B) humans preferred only long necked ones

C) short necks suddenly changed into long necks

D) of stretching of necks over many generations by short necked ones.

Answer: D) of stretching of necks over many generations by short necked ones.

Explanation: Lamarck proposed that the ancestors of giraffes stretched their necks to reach higher leaves, and

this acquired trait was passed on to their offspring.

1. Natural selection is random or systematic, explain your answer.

Answer: Natural selection is systematic, not random. While the production of genetic variations (mutations) is random, the process of natural selection itself is non-random. It consistently favors individuals with traits that are better suited to their environment. These individuals have higher survival and reproductive rates, so their favorable traits become more common in the population over generations. This is a systematic process that leads to adaptation. It is the opposite of genetic drift, which is a random change in allele frequencies.

2. How is convergent evolution different from divergent evolution?

Answer: Convergent evolution is when unrelated species evolve similar traits independently, usually because they adapt to similar environments or ecological niches. This results in analogous structures (e.g., wings of birds and insects). Divergent evolution is when a single ancestral species evolves into many different species, each adapted to different environments. This results in homologous structures (e.g., forelimbs of mammals). In short, convergent evolution leads to similarities, while divergent evolution leads to differences from a common ancestor.

3. Explain endosymbiont hypothesis.

Answer: The endosymbiont hypothesis explains the origin of eukaryotic cells. It proposes that mitochondria and

chloroplasts were once free-living prokaryotes that were engulfed by a larger ancestral eukaryotic cell. Instead of being digested, they formed a symbiotic relationship with the host cell. The host provided protection and nutrients, while the engulfed prokaryotes provided energy (mitochondria) or photosynthesis (chloroplasts). Evidence for this includes the double membrane, circular DNA, and 70S ribosomes of these organelles.

4. What are homologous structures, explain with an example.

Answer: Homologous structures are organs or body parts in different species that have a similar underlying anatomical structure and evolutionary origin, but may perform different functions. They provide evidence for divergent evolution from a common ancestor. An example is the forelimbs of mammals: the human arm, the whale flipper, the bat wing, and the horse leg all have the same basic bone structure (humerus, radius, ulna, carpals, metacarpals, phalanges), but they are adapted for different functions like grasping, swimming, flying, and running.

5. What are vestigial organs? Give few examples from human body.

Answer: Vestigial organs are structures that have lost most or all of their original function during the course of evolution. They are remnants of organs that were functional in ancestors but are no longer needed. In humans, examples include the vermiform appendix (once used for digesting cellulose), the coccyx (tailbone, remnant of a tail), the nictitating membrane (plica semilunaris, remnant of a third eyelid), and the muscles that move the ears (auricular muscles).

6. Enlist few characteristics found only in mammals.

Answer: Characteristics found only in mammals include:

1. Mammary glands: Present in females, used to produce milk to nourish young.

2. Hair or fur: Made of keratin, covering the body.

3. Three middle ear bones: Malleus, incus, and stapes.

4. Neocortex: A highly developed region of the brain.

5. Diaphragm: A muscular sheet separating the thoracic and abdominal cavities.

6. Endothermy: Warm-blooded.

7. Four-chambered heart.

1. How natural selection operates to create new species? Discuss in details.

Answer: Natural selection is the primary mechanism of evolution proposed by Charles Darwin. It operates on the genetic variation within a population to produce adaptations and, over long periods, new species.

Step-by-Step Process:

1. Overproduction: Organisms produce more offspring than can possibly survive.

2. Variation: Individuals within a population exhibit variations in their traits. These variations arise from random mutations and genetic recombination.

3. Competition (Struggle for Existence): Due to overproduction, individuals must compete for limited resources like food, water, and shelter.

4. Survival of the Fittest (Differential Survival): Individuals with variations that are better suited to their environment are more likely to survive and reproduce. These individuals are said to have higher

fitness.

5. Differential Reproduction: The survivors pass their favorable traits to their offspring. Over generations, the proportion of individuals with these advantageous traits increases in the population.

6. Adaptation: The population becomes better adapted to its environment.

7. Speciation: If populations become reproductively isolated (e.g., by geographic barriers), they may diverge genetically over time. Accumulated differences can lead to the formation of new species, as they can no longer interbreed.

Types of Natural Selection:

Directional Selection: Favors one extreme phenotype. Stabilizing Selection: Favors intermediate phenotypes. Disruptive Selection: Favors both extreme phenotypes.

In summary, natural selection is a systematic process that acts on random variations to drive adaptation and speciation. It is the cornerstone of evolutionary biology.

2. Explain evidences from molecular biology in support of evolution.

Answer: Molecular biology provides strong evidence for evolution by revealing the shared biochemical and genetic similarities among diverse organisms.

1. DNA and Genetic Code:

All organisms use the same genetic material (DNA) and the same genetic code (triplet codons) to specify amino acids.

The universality of the genetic code suggests a common ancestry.

2. Protein Sequences:

Comparisons of protein sequences (e.g., cytochrome c, hemoglobin) show that the degree of similarity reflects evolutionary relatedness. Organisms that are more closely related have fewer amino acid differences in their proteins.

3. Molecular Clocks:

The rate of accumulation of mutations in DNA is relatively constant over time. This allows scientists to estimate the time of divergence between species.

4. Vestigial Genes:

Pseudogenes are non-functional remnants of genes that were once functional. Their presence provides evidence of evolutionary history.

5. Homeotic Genes:

Genes that control body development (e.g., Hox genes) are highly conserved across diverse species.

6. Endogenous Retroviruses:

Viral DNA sequences inserted into the genome are inherited. Shared insertion sites provide evidence of common ancestry.

In summary, molecular biology provides a wealth of evidence for evolution, from the universality of the genetic code to the comparative analysis of DNA and protein sequences.

3. Suppose a new mammalian species has originated in planes of sub-continent, what kind of barriers can restrict its dispersal in other regions of the world

Answer: If a new mammalian species originates in the plains of the sub-continent, its dispersal to other regions of the world could be restricted by several types of barriers.

1. Geographical Barriers:

Mountain Ranges: The Himalayas to the north act as a formidable physical barrier. Oceans and Seas: The Indian Ocean to the south, Arabian Sea to the west, and Bay of Bengal to the east restrict movement. Deserts: The Thar Desert to the west is a harsh, dry barrier.

2. Climatic Barriers:

Temperature Extremes: The cold climate of the Himalayas and the extreme heat of the deserts are unsuitable for many species. Rainfall Patterns: Differences in precipitation can create unsuitable habitats.

3. Ecological Barriers:

Competition: Existing species in new regions may outcompete the new species for resources. Predators: New predators may limit the survival of the dispersing species. Food Availability: Lack of suitable food sources in new areas.

4. Biological Barriers:

Reproductive Isolation: If the species cannot find mates or interbreed, it cannot establish a

population. Diseases: New pathogens may be encountered.

5. Human-Made Barriers:

Urbanization: Cities and infrastructure can fragment habitats. Agriculture: Farmland can be a barrier.

In summary, a combination of geographical, climatic, ecological, and biological barriers can restrict the dispersal of a new mammalian species from the sub-continent to other regions of the world. These barriers contribute to the unique biodiversity of the sub-continent.