Lecture Notes: Convergence in Evolutionary Biology

Introduction to Convergence

Definition: Convergence is the independent evolution of similar features in species of different lineages.
Analogy: Evolution is like a tree starting with a shape and evolving upwards, where similar features arise multiple times independently.

Ichthyosaur and Dolphin:
- Ichthyosaurs are marine reptiles from the Triassic, more related to lizards.
- Dolphins are mammals but have similar body shapes to ichthyosaurs (e.g., dorsal fin, snout).
- This similarity is not due to shared ancestry but similar evolutionary pressures.
Fish-like Forms:
- Tuna, Sharks, and Dolphins: All have streamlined bodies adapted for fast swimming as alpha predators in oceans.
- Tunaform Shape: Common shape evolved in different lineages for speed and efficiency in aquatic environments.

Human and Squid Eyes: Both have lenses; light passes through and is reflected at the back of the eye.
Insects vs. Human Eyes: Insects have compound eyes with many lenses; humans have single-lens eyes.
Gene Involvement: PAX6 gene involved in eye placement across many species.
- Controls head and eye development from early embryonic stages.

Definition: Similar traits develop independently in related species due to similar developmental constraints.
Example: Use of PAX6 gene to determine eye placement across various species considered parallel evolution.

Ammonites and Nautiloids:
- Both had spiral shells evolved independently despite distant relation.
- Baculites (ammonites) developed straight shells similar to orthocone nautiloids.
Herbivorous Giants with Claws:
- Examples: Giant ground sloths, calicotheres, therinsosaurs.
- Adapted for standing on hind legs with large claws, though distinct lineages.

Understanding past ecological niches through convergence.
Example: Giant sloths, calicotheres, and therinsosaurs indicate an ecological niche for large bipedal herbivores with claws, now extinct.

Convergence provides insights into evolutionary pressures and potential ecological niches.
It is key to understanding the evolution of life on Earth and potentially alien life.

These notes cover the key examples and concepts of convergence in evolutionary biology as discussed in the lecture.