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Q1.6(b):
The shells of crabs found around a particular coastal location in Japan seem mostly to resemble the legendary face of a Samurai. Given below are two explanations of this observed fact. Which of these strikes you as a scientific explanation ? (b) After the sea tragedy, fishermen in that area, in a gesture of honour to their dead hero, let free any crab shell caught by them which accidentally had a shape resembling the face of a Samurai. Consequently, the particular shape of the crab shell survived longer and therefore in course of time the shape was genetically propagated. This is an example of evolution by artificial selection. [Note : This interesting illustration taken from Carl Sagan’s ‘The Cosmos’ highlights the fact that often strange and inexplicable facts which on the first sight appear ‘supernatural’ actually turn out to have simple scientific explanations. Try to think out other examples of this kind].

Solution :

Step 1: Analyzing the Proposed Mechanism

The provided explanation attributes the prevalence of Samurai-like crab shells to a specific sequence of anthropogenic (human-induced) interactions. The mechanism operates through the following causal chain:

  • Selection Pressure: Fishermen intentionally discarded crabs that displayed a resemblance to the Samurai face. [Per the principles of Selective Breeding/Artificial Selection].
  • Differential Survival: Crabs that exhibited the Samurai-like traits were granted higher survivability and reproductive success compared to those that did not. [Per the mechanism of Natural Selection acting upon artificial constraints].
  • Genetic Propagation: The traits were encoded in the organism's genome and passed down to subsequent generations. [Per the Mendelian laws of inheritance and population genetics].

Step 2: Theoretical Justification via Evolutionary Biology

To determine if this is scientific, we evaluate it against the criteria of the Scientific Method:

Criterion Analysis
Falsifiability The hypothesis can be tested by examining the fossil records or genetic markers of the crab population over time.
Empirical Basis The explanation relies on observable behaviors (fisherman actions) and biological processes (heredity).
Mechanism It invokes Artificial Selection, a well-documented evolutionary process where human preference serves as the environmental filter for phenotypic expression.

Step 3: Verification of the Scientific Status

The explanation is fundamentally scientific because it avoids supernatural intervention or teleological assumptions. Instead, it provides a materialistic, cause-and-effect account based on:

  1. Variation: The presence of random genetic mutations that initially created shells resembling various shapes.
  2. Selection: The cultural preference of the fishermen acting as an external selective force.
  3. Inheritance: The biological passing of successful genetic configurations to offspring.

Step 4: Comparative Visual representation of Selection

Original Population (Random Phenotypes) -> Human Selection -> Increased Frequence of Samurai Phenotype

Final Solution: The provided explanation is a scientific one. It explains the biological phenomenon through the established evolutionary mechanism of 'Artificial Selection,' where human behavior provides the selective pressure that leads to the amplification of a specific trait within a population, consistent with the principles of genetics and natural selection.


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