NCERT Solutions

Darwinian selection states that inherent variations exist in a population. When the environment changes, nature selects the individuals with variations better suited for survival.

1. A bacterial colony contains millions of cells. Due to spontaneous mutations, a few bacteria may possess a gene that makes them resistant to a specific antibiotic.
2. Pre-existing Variation: The resistance is not created by the antibiotic; it exists as a random variation beforehand.
3. Selection Pressure: When the antibiotic is applied, the non-resistant bacteria die.
4. Survival of the Fittest: The resistant bacteria survive, reproduce, and increase in number.
5. Over generations, the entire population becomes antibiotic-resistant. This is a classic example of Natural Selection.

(This is an activity-based question. Here are notable examples.)

• Homo naledi (2015): Discovery of a new human-like species in South Africa, suggesting a complex evolutionary tree.
• Tiktaalik: A “fishapod” fossil that bridges the gap between water-dwelling fish and land-dwelling tetrapods.
• Dragon Man (Homo longi) (2021): A massive skull found in China that might be a closer relative to humans than Neanderthals.

Biological Species Concept: A species is a group of organisms that can interbreed among themselves under natural conditions to produce fertile offspring.

Members of a species share a common gene pool and are reproductively isolated from other such groups.

Self-consciousness (awareness of oneself as a separate individual) is highly developed in humans. However, studies suggest varying degrees of self-awareness in other animals:

• Dolphins and Whales: Exhibit high intelligence and can recognize themselves in mirrors.
• Chimpanzees and Orangutans: Pass the “Mirror Test” (recognizing a mark on their face in a mirror).
• Elephants: Show empathy and recognition of self.

(Self-activity). Focus on drawing:

• Homologous Organs: Forelimbs of Human, Cheetah, Whale, and Bat.
• Adaptive Radiation: Beaks of Darwin’s Finches.
• Miller’s Experiment: The spark discharge apparatus.

Definition: Adaptive radiation is the process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats).

Example: Darwin observed small black birds in the Galapagos Islands.

• Ancestral Stock: Seed-eating finches from the mainland (South America).
• Radiation: Due to competition and different food sources on different islands, their beaks evolved.
• Result: Evolution of insectivorous, vegetarian, cactus-eating, and wood-pecker finches from the original seed-eating stock.

No, human evolution is not typically considered a classic case of adaptive radiation.

Reason: Adaptive radiation involves the divergence of a single ancestral species into multiple diverse species to occupy different ecological niches simultaneously (like Darwin’s finches). Human evolution is largely a progressive (anagenesis) series of changes where one species evolved into the next (e.g., Australopithecus \(\to\) Homo habilis \(\to\) Homo erectus \(\to\) Homo sapiens) over time, rather than a rapid radial diversification into many different species living at the same time in different niches.

• Gene Flow: Transfer of genetic variation (alleles) from one population to another due to migration.
• Genetic Drift: Random change in allele frequencies in a small population by chance events (e.g., Founder Effect, Bottleneck Effect).

1. Darwin’s Finches: (Galapagos Islands).
2. Australian Marsupials: Evolution of Tasmanian wolf, Kangaroo, Koala, etc., from a common ancestral marsupial within the isolated Australian continent.

Also called the Modern Synthetic Theory. It synthesizes Darwin’s Natural Selection with Mendel’s Genetics. It states that evolution depends on:

• Genetic Variations (Mutation, Recombination).
• Natural Selection.
• Reproductive Isolation.

Stanley Miller (1953) simulated primitive Earth conditions in a lab.

• Setup: A closed flask containing Methane (\(CH_4\)), Ammonia (\(NH_3\)), Hydrogen (\(H_2\)) and Water vapour (\(H_2O\)) at 800°C.
• Energy: Electric discharge (spark) using electrodes to mimic lightning.
• Observation: Formation of simple organic molecules like Amino Acids (Glycine, Alanine, Aspartic acid).
• Conclusion: Supported Oparin-Haldane theory that life arose from non-living organic molecules (Abiogenesis).

Statement: Allele frequencies in a population are stable and remain constant from generation to generation in the absence of evolutionary influences. (Genetic Equilibrium).

Equation: \(p^2 + 2pq + q^2 = 1\) (where \(p\) and \(q\) are allele frequencies).

1. Gene Migration (Gene Flow).
2. Genetic Drift.
3. Mutation.
4. Genetic Recombination.
5. Natural Selection.