Convergent evolution explains why unrelated organisms can end up looking and functioning similarly. For AP Biology, focus on how similar selective pressures shape similar phenotypes despite different evolutionary histories.

Core idea: similar problems, similar solutions

Convergence is an outcome of natural selection: when environments impose comparable challenges (finding food, moving efficiently, avoiding predators), certain trait forms tend to be favored repeatedly.

What the syllabus is emphasising

• Selective pressures can be similar across different habitats or communities (e.g., open water, deserts, aerial environments).

• Those pressures can favor similar adaptations (structures, behaviors, or physiological traits that increase fitness in a specific environment).

• The organisms showing the similarity are from different populations or species, meaning the traits arose independently.

Recognising convergent evolution in biological data

Key patterns you should be able to identify

• Similar phenotype, different ancestry: the organisms share a trait that improves performance in a similar environment, but that trait was not present in their most recent common ancestor.

• Repeated evolution: similar trait “solutions” appear in multiple lineages exposed to similar conditions.

This labeled panel shows multiple pairs of ecologically similar mammals from Australia and the Americas (e.g., wolf vs Tasmanian wolf, flying squirrel vs sugar glider). It illustrates how similar ecological niches can repeatedly favor similar adaptations in distantly related lineages, producing striking phenotypic similarity across regions. Source

• Functional similarity: the traits perform similar roles (e.g., streamlined bodies for efficient swimming).

A common AP Biology distinction is that convergent evolution typically produces analogous structures rather than homologous ones.

This figure compares wings from a bat, a bird, and a honeybee to show that similar function (flight) does not guarantee shared evolutionary origin. Vertebrate wings share underlying forelimb bone homology, while the insect wing achieves flight with a fundamentally different structure—making it analogous rather than homologous. Source

Examples of convergent adaptations (conceptual level)

• Streamlining in fast swimmers: sharks (fish) and dolphins (mammals) both have body shapes that reduce drag in water.

This labeled comparison highlights anatomical features that independently evolved in dolphins (mammals) and ichthyosaurs (marine reptiles) under similar hydrodynamic selective pressures. It reinforces that similar body plans can arise without recent common ancestry when the functional demands of fast swimming are similar. Source

• Succulent, spiny desert forms: some unrelated plant lineages independently evolve water storage tissues and spines in arid climates.

• Wings for flight: functional wings evolved in different groups under selection for aerial locomotion.

Why similar selective pressures can produce similar phenotypes

Environmental “filters” and performance trade-offs

Selection tends to favor traits that improve survival and reproduction under specific constraints:

• Physical constraints: fluid dynamics in water/air can favor similar body forms that reduce drag or increase lift.

• Resource constraints: limited water or nutrients can favor similar strategies of storage, reduced surface area, or protective coverings.

• Predation pressures: similar predator regimes can favor comparable defenses (camouflage, armor-like coverings, toxins).

Constraints and limited “design space”

Convergence is more likely when:

• There are limited effective ways to perform a function (e.g., efficient high-speed swimming).

• Developmental and structural constraints channel variation toward certain outcomes.

• Selection is strong and consistent over time, repeatedly favoring particular phenotypes.

Convergent evolution and interpreting similarity

Avoiding a common misconception

• Similarity does not automatically imply close relatedness.

• Convergent traits can mislead classification if you rely only on appearance, because selection can make unrelated organisms look alike.

How biologists justify convergence

Evidence that a similarity is convergent often includes:

• The trait appears in distantly related groups but is absent in many closer relatives.

• Comparative anatomy shows different underlying construction despite similar function.

• Genetic and developmental pathways differ even when the outward phenotype is similar (the phenotype is what selection “sees,” but it can be built in multiple ways).