Evolution of Life Archives

1. Which one of the following pairs correctly represents an example of an

Which one of the following pairs correctly represents an example of analogous organs ?

Forelimb of horse and human arm

Human hands and wings of birds

Wings of birds and wings of insects

Flipper of whale and forelimb of frog

This question was previously asked in

UPSC CISF-AC-EXE – 2023

Download PDF Attempt Online

Analogous organs are organs that perform similar functions but have different evolutionary origins and structures. Wings of birds and wings of insects both serve the function of flight, but their underlying structures are fundamentally different. Bird wings are modified forelimbs with bones covered by feathers, while insect wings are chitinous extensions of the body wall, supported by veins. This difference in structure despite similar function makes them analogous organs.

– Analogous organs arise from convergent evolution, where unrelated organisms evolve similar traits due to similar environmental pressures.
– They have similar functions but different basic structures and origins.
– Homologous organs, in contrast, have similar structures and origins (due to common ancestry) but may have different functions.

Examples of homologous organs include the forelimbs of vertebrates (human arm, whale flipper, bat wing, horse leg), which share a common bone structure despite different functions. Examples of analogous organs include the eye of a squid and the eye of a vertebrate, or the spines of a cactus and the spines of a euphorbia.

2. ‘Microsatellite DNA’ is used in the case of which one of the foll

‘Microsatellite DNA’ is used in the case of which one of the following?

Studying the evolutionary relationships among various species of fauna

Stimulating ‘stem cells’ to transform into diverse functional tissues

Promoting clonal propagation of horticultural plants

Assessing the efficacy of drugs by conducting series of drug trials in a population

This question was previously asked in

UPSC IAS – 2023

Download PDF Attempt Online

The correct answer is A) Studying the evolutionary relationships among various species of fauna.

Microsatellite DNA (also known as Short Tandem Repeats or STRs) consists of repeating sequences of a few nucleotides (typically 2-6 bp) found throughout the genome. These regions are highly variable in length among individuals and even among closely related species due to differences in the number of repeat units. This high variability makes microsatellites excellent genetic markers for population genetics studies, genetic diversity analysis, parentage testing, individual identification, and studying evolutionary relationships, particularly among populations within a species or among closely related species where there is sufficient variability.

Options B, C, and D are not primary applications of microsatellite DNA analysis. Stem cell differentiation (B) involves gene expression and signaling pathways. Clonal propagation (C) involves vegetative reproduction techniques, although microsatellites could be used for verifying clonality. Drug efficacy assessment (D) is part of clinical trials and often involves patient response, pharmacokinetics, and sometimes pharmacogenomics (which might use various genetic markers, but microsatellites are not typically the primary tool for drug *efficacy* assessment itself).

3. The word ‘Denisovan’ is sometimes mentioned in media in reference to

The word ‘Denisovan’ is sometimes mentioned in media in reference to

fossils of a kind of dinosaurs

an early human species

a cave system found in North-East India

a geological period in the history of Indian subcontinent

This question was previously asked in

UPSC IAS – 2019

Download PDF Attempt Online

The correct answer is B) an early human species.

Denisovans are an extinct species or subspecies of archaic humans. Their existence was first suggested in 2010 based on mitochondrial and nuclear DNA analysis of a fossil found in Denisova Cave in Siberia. Genetic studies have shown that Denisovans interbred with modern humans and Neanderthals.

The discovery of Denisovans, Neanderthals, and their interbreeding with Homo sapiens has significantly advanced our understanding of recent human evolution and migration patterns. Traces of Denisovan DNA are found in the genomes of present-day populations, particularly in parts of Southeast Asia and Oceania.

4. Which of the following phenomena might have influenced the evolution o

Which of the following phenomena might have influenced the evolution of organisms?

1. Continental drift
2. Glacial cycles

Select the correct answer using the code given below.

1 only

2 only

Both 1 and 2

Neither 1 nor 2

This question was previously asked in

UPSC IAS – 2014

Download PDF Attempt Online

The correct answer is C.

Both Continental drift (1) and Glacial cycles (2) are major geological and climatic phenomena that have profoundly influenced the evolution of organisms. Continental drift alters the distribution of landmasses and oceans, creating or removing physical barriers, changing climate patterns, and leading to the isolation or mixing of populations, which drives speciation and extinction. Glacial cycles cause significant changes in climate, sea levels, and habitats, leading to species migrations, adaptations, extinctions, and the formation of new species through the creation of refugia and altered selective pressures.

The theory of plate tectonics explains continental drift and is a cornerstone of modern geology. Glacial cycles have occurred repeatedly throughout Earth’s history, most notably during the Pleistocene epoch (the ‘Ice Age’).

5. One advantage of sexual reproduction over asexual reproduction is that

One advantage of sexual reproduction over asexual reproduction is that it helps species to survive over long evolutionary time. This is because sexual reproduction produces :

more offspring in each reproductive cycle.

robust and healthy offspring.

genetically similar offspring.

more variation in offspring.

This question was previously asked in

UPSC NDA-1 – 2023

Download PDF Attempt Online

The correct answer is D) more variation in offspring.

Sexual reproduction involves the fusion of gametes from two parents, leading to a combination of genetic material. This process, along with mechanisms like crossing over during meiosis, generates offspring with unique genetic combinations, increasing genetic variation within the population.

Genetic variation is crucial for the long-term survival of a species, especially in changing environments. A diverse gene pool increases the likelihood that some individuals will possess traits that allow them to adapt to new conditions, resist diseases, or survive environmental stresses, thereby ensuring the continuation of the species over evolutionary time. Asexual reproduction, while often faster and producing more numerous offspring in stable environments (countering option A), results in genetically similar offspring, making the population less adaptable to change.

6. Which one among the following is NOT an attribute of the ‘Land Ra

Which one among the following is NOT an attribute of the ‘Land Races’?

Land Races have a ‘certain genetic integrity’

They can be very well recognised morphologically

They are highly adapted to specific soil types and local environmental variables

They don’t have specific time of seeding and date of maturity

This question was previously asked in

UPSC Geoscientist – 2021

Download PDF Attempt Online

Landraces are typically highly adapted to their local environments, including the specific climatic cycles. This adaptation results in relatively specific timing for key phenological events like seeding and maturity that are synchronized with the local season. Therefore, stating they “don’t have specific time of seeding and date of maturity” is incorrect.

Landraces are traditional, locally adapted varieties of crops or animals that have evolved through a combination of natural selection under local conditions and human selection. They possess genetic diversity and resilience suited to their specific agroecological niche.

Attributes of landraces include distinct genetic identities, recognizable morphological traits, high adaptation to local conditions (soil, climate, pests, diseases), and they often have specific growth cycles adapted to the local season. Their genetic diversity makes them valuable resources for breeding programs.

7. Which one of the following is NOT a condition necessary for natural se

Which one of the following is NOT a condition necessary for natural selection to occur?

More organisms are born than can survive

Organisms should not vary in their characteristics within a species

Variation is inherited

Differences in reproduction and survival are due to variation among organisms

This question was previously asked in

UPSC Geoscientist – 2021

Download PDF Attempt Online

For natural selection to occur, organisms *must* vary in their characteristics within a species. Variation is the raw material upon which selection acts.

The necessary conditions for natural selection are: variation among individuals, inheritance of variation, differential survival and reproduction based on that variation, and often, limited resources leading to competition (more offspring born than can survive).

If there were no variation within a species, all individuals would be identical, and there would be no basis for differential survival or reproduction based on traits, thus no natural selection leading to evolutionary change.

8. Which one of the following statements about variations is not true ?

Which one of the following statements about variations is not true ?

Variation is minimum in asexual reproduction.

All variations in a species have equal chances of survival.

Changes in genetic constitution result in variation.

Variants can be selected by environmental factors.

This question was previously asked in

UPSC CDS-2 – 2021

Download PDF Attempt Online

A) Variation is minimum in asexual reproduction: Asexual reproduction involves a single parent producing genetically identical offspring (clones) through mitosis. The only source of variation is random mutation. Sexual reproduction, involving two parents and meiosis with crossing over and independent assortment, creates much greater genetic variation through new combinations of genes. So, variation is indeed minimal in asexual reproduction compared to sexual reproduction. This statement is true.
B) All variations in a species have equal chances of survival: This statement is false. Survival is not random with respect to variations. Variations confer different traits on individuals. Depending on the environmental conditions, some traits (and thus the variations that cause them) may be advantageous, increasing an individual’s chances of survival and reproduction. Other variations may be disadvantageous, decreasing the chances of survival. This differential survival and reproduction based on variations is the basis of natural selection.
C) Changes in genetic constitution result in variation: Variations are heritable differences between individuals. These differences arise from changes in the genetic material (DNA), such as mutations (changes in nucleotide sequence) or rearrangements of chromosomes, as well as the combination of genes inherited from parents in sexually reproducing organisms. So, this statement is true.
D) Variants can be selected by environmental factors: This is a fundamental principle of evolution by natural selection. Environmental conditions act as selective pressures, favouring individuals with certain variations that make them better adapted to that environment. These individuals are more likely to survive and pass on their advantageous variations to their offspring. This statement is true.
The statement that is NOT true is B.

– Variation arises from changes or combinations of genes.
– Sexual reproduction generates more variation than asexual reproduction.
– Natural selection acts on variations; survival is not equally likely for all variations.
– Environmental factors drive the selection of variants.

Variations are the raw material for evolution. Without variation, natural selection cannot occur, and populations would not be able to adapt to changing environments.

9. Wings of birds and bats are considered analogous structures because th

Wings of birds and bats are considered analogous structures because they have

common origin and common function

different origin and common function

common origin and different function

different origin and different function

This question was previously asked in

UPSC CDS-2 – 2020

Download PDF Attempt Online

Wings of birds and bats are considered analogous structures because they have different origin and common function.

Analogous structures are features in different species that perform the same function but have evolved independently from different ancestors. This is a result of convergent evolution, where different organisms adapt to similar environments or ecological niches. Bird wings evolved from forelimbs of reptilian ancestors, while bat wings evolved from the forelimbs of mammalian ancestors, and their skeletal structures are fundamentally different, reflecting their distinct evolutionary paths. However, both structures serve the purpose of flight. Homologous structures, in contrast, have a common evolutionary origin but may have different functions (e.g., the forelimbs of humans, bats, whales, and birds all originated from a common tetrapod ancestor but are used for different activities like grasping, flying, swimming).

Studying analogous and homologous structures helps scientists understand evolutionary relationships and the processes of adaptation and diversification. Analogous structures illustrate how natural selection can lead to similar solutions for similar environmental challenges in unrelated organisms.