Glossary
Adaptive Radiation
Rapid diversification of an ancestral species into many new forms, often occurring when new ecological niches become available.
Example:
The evolution of numerous marsupial species in Australia, filling diverse ecological roles, is a prime example of adaptive radiation.
Allopatric Speciation
Speciation that occurs when populations are geographically separated, preventing gene flow and leading to independent evolutionary paths.
Example:
A mountain range forming and dividing a single squirrel population, eventually leading to two distinct species, is an instance of allopatric speciation.
Biological Species Concept
A definition of species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring.
Example:
Under the Biological Species Concept, lions and tigers are considered separate species because their hybrid offspring, ligers, are infertile.
Divergent Evolution
When populations adapt to different environments, leading to new forms from a common ancestor.
Example:
The varied beaks of Darwin's finches, each adapted to different food sources on the Galápagos Islands, are a classic case of divergent evolution.
Gradualism
A model of evolution that proposes that change occurs slowly and steadily over long periods through the accumulation of small modifications.
Example:
The slow, continuous increase in brain size in hominids over millions of years is an example of gradualism.
Postzygotic Isolation
Reproductive barriers that prevent hybrid zygotes from developing into viable, fertile adults after fertilization has occurred.
Example:
When the hybrid offspring of two different plant species are sterile and cannot produce their own seeds, this demonstrates postzygotic isolation.
Prezygotic Isolation
Reproductive barriers that prevent mating or fertilization from occurring between different species before a zygote can form.
Example:
If two bird species have different courtship dances, preventing them from recognizing each other as mates, this is a form of prezygotic isolation.
Punctuated Equilibrium
A model of evolution suggesting that species remain relatively unchanged for long periods (stasis), interrupted by brief periods of rapid evolutionary change.
Example:
The sudden appearance of many new insect species in the fossil record after a major environmental shift could illustrate punctuated equilibrium.
Reproductive Isolation
The existence of biological factors (barriers) that impede two species from producing viable, fertile offspring.
Example:
Different mating calls in frog populations can lead to reproductive isolation, preventing them from interbreeding.
Species
A group of organisms defined by their ability to sexually reproduce and create viable, fertile offspring.
Example:
A pack of wolves belongs to the same species because they can interbreed and produce fertile pups.
Sympatric Speciation
Speciation that occurs within the same geographic area, often due to factors like disruptive selection or mating preferences, without a physical barrier.
Example:
Certain plant species can undergo sympatric speciation through polyploidy, where an increase in chromosome number immediately creates a new species unable to interbreed with the parent population.