Convergence, Natural Selection, 'Survival of the Fittest'

In the book Improbable Destinies, one example of convergent evolution is the similarity between the eyes of octopuses and vertebrates. Both have complex camera-like eyes, despite their very different evolutionary lineages.

Convergent Evolution refers to the phenomenon where unrelated or distantly related organisms independently evolve similar traits or adaptations due to having to cope with similar environmental challenges or ecological niches. 

Divergent Evolution occurs when two or more related species become more dissimilar over time, often due to adapting to different environments or ecological niches. This can result in homologous structures—features that are similar due to shared ancestry, but have evolved differently.

For Example: The forelimbs of mammals (like the wings of bats and the arms of humans) show divergent evolution. They have a common origin but have adapted to different functions.

Both octopuses and vertebrates have evolved complex, camera-like eyes with similar features such as a lens, retina, and a mechanism for focusing light. This demonstrates convergent evolution by:

• Structure Similarity: Despite their different ancestry, both octopuses and vertebrates have evolved eyes that function in similar ways. They can form clear images, adjust to light levels, and have specialized cells for detecting light.

• Different Origins: Octopuses and vertebrates diverged from a common ancestor hundreds of millions of years ago. The evolutionary paths that led to their eyes are distinct; vertebrates evolved from a lineage of animals with simpler eyes, while cephalopods come from a completely different lineage.

• Functional Similarity: The similar structure serves the same function in both cases: providing detailed visual information to the organism, despite the fact that these organisms have very different genetic backgrounds.

Natural selection explains the development of convergent features by favoring adaptations that are beneficial for survival and reproduction in similar environmental conditions, even if the organisms involved are not closely related.

• Environmental Pressure: Both octopuses and vertebrates inhabit environments where high-quality vision is crucial for survival. For example, octopuses often hunt prey in varying light conditions and need sharp vision for detecting predators and finding food. Similarly, vertebrates such as humans have evolved complex eyes to navigate their environment, find food, and avoid predators.

• Selective Advantage: The camera-like eye structure in both groups provides a significant evolutionary advantage. It allows for precise vision, better depth perception, and improved ability to react to visual stimuli, which are essential traits for survival and reproduction.

• Independent Evolution: Although the pathways to these eyes are different, natural selection has favored the development of similar eye structures because they offer similar advantages. Despite their different evolutionary origins, the similar selective pressures have led to the evolution of analogous features.