Q.14 The evolution of eyes in octopus and in human is an example of ________.
(A) divergent evolution (B) convergent evolution
(C) adaptive radiation (D) genetic drift

The evolution of eyes in octopus and human exemplifies convergent evolution, where unrelated species develop similar complex structures independently due to similar selective pressures for vision.​

This is a classic example in evolutionary biology, often featured in exams like CSIR NET Life Sciences.

Option Analysis

• (A) Divergent evolution: Occurs when species from a common ancestor evolve different traits, leading to homologous structures (e.g., forelimbs of humans and bats). Octopus (mollusk) and humans (vertebrate) diverged over 500 million years ago without shared eye ancestry, so eyes are analogous, not homologous.​

• (B) Convergent evolution: Unrelated species independently evolve similar traits for the same function under similar environments. Octopus and human camera eyes both feature lenses, pupils, and retinas for image formation, despite inverted retina orientations and different developmental paths (Pax6 gene conserved but pathways distinct).​

• (C) Adaptive radiation: Rapid diversification from one ancestor into multiple species exploiting new niches (e.g., Darwin’s finches). This involves speciation from a single lineage, not parallel eye evolution in distant taxa.​

• (D) Genetic drift: Random allele frequency changes in small populations, unrelated to adaptive trait similarity like eyes. It lacks selective direction for complex structures.​

Correct Answer: (B) convergent evolution​

The evolution of eyes in octopus and human stands as a hallmark of convergent evolution, where distantly related species develop strikingly similar camera eyes independently. This phenomenon highlights natural selection’s power in shaping vision across invertebrates and vertebrates, despite no recent common ancestor.​

Core Similarities

Both octopus and human eyes feature a single lens focusing light onto a retina lined with photoreceptors, forming sharp images—unlike simpler light-sensitive patches in other animals. Octopus eyes even lack the human blind spot due to forward-facing nerves. Gene expression studies reveal shared pathways like Pax6, yet embryological origins differ: vertebrate eyes invaginate outward, cephalopod eyes inward.​

Why Convergent, Not Divergent?

Divergent evolution produces homologous structures from one ancestor, like mammal and bird wings. Here, octopus-human eyes are analogous: similar function, different blueprints, evolving separately post-Cambrian divergence.​

Other Concepts Ruled Out

• Adaptive radiation drives one lineage into diverse forms (e.g., cichlid fishes in lakes), not cross-phyla trait convergence.​

• Genetic drift causes random gene shifts in small groups, irrelevant to vision’s adaptive complexity.​

This example aids CSIR NET preparation, emphasizing analogous organs in evolution questions.