Skip to ContentGo to accessibility page
OpenStax Logo
Biology 2e

Key Terms

Biology 2eKey Terms

Key Terms

adaptation
heritable trait or behavior in an organism that aids in its survival and reproduction in its present environment
adaptive radiation
speciation when one species radiates to form several other species
allopatric speciation
speciation that occurs via geographic separation
allopolyploid
polyploidy formed between two related, but separate species
aneuploidy
condition of a cell having an extra chromosome or missing a chromosome for its species
autopolyploid
polyploidy formed within a single species
behavioral isolation
type of reproductive isolation that occurs when a specific behavior or lack of one prevents reproduction from taking place
convergent evolution
process by which groups of organisms independently evolve to similar forms
dispersal
allopatric speciation that occurs when a few members of a species move to a new geographical area
divergent evolution
process by which groups of organisms evolve in diverse directions from a common point
gametic barrier
prezygotic barrier occurring when closely related individuals of different species mate, but differences in their gamete cells (eggs and sperm) prevent fertilization from taking place
gradual speciation model
model that shows how species diverge gradually over time in small steps
habitat isolation
reproductive isolation resulting when species' populations move or are moved to a new habitat, taking up residence in a place that no longer overlaps with the same species' other populations
homologous structures
parallel structures in diverse organisms that have a common ancestor
hybrid
offspring of two closely related individuals, not of the same species
hybrid zone
area where two closely related species continue to interact and reproduce, forming hybrids
natural selection
reproduction of individuals with favorable genetic traits that survive environmental change because of those traits, leading to evolutionary change
postzygotic barrier
reproductive isolation mechanism that occurs after zygote formation
prezygotic barrier
reproductive isolation mechanism that occurs before zygote formation
punctuated equilibrium
model for rapid speciation that can occur when an event causes a small portion of a population to be cut off from the rest of the population
reinforcement
continued speciation divergence between two related species due to low fitness of hybrids between them
reproductive isolation
situation that occurs when a species is reproductively independent from other species; behavior, location, or reproductive barriers may cause this to happen
speciation
formation of a new species
species
group of populations that interbreed and produce fertile offspring
sympatric speciation
speciation that occurs in the same geographic space
temporal isolation
differences in breeding schedules that can act as a form of prezygotic barrier leading to reproductive isolation
variation
genetic differences among individuals in a population
vestigial structure
physical structure present in an organism but that has no apparent function and appears to be from a functional structure in a distant ancestor
vicariance
allopatric speciation that occurs when something in the environment separates organisms of the same species into separate groups
PreviousNext
Order a print copy
Citation/Attribution
Reuse and redistribution of this content in digital or print format:
  • This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's prior written permission.
  • This book uses the Creative Commons Attribution-NonCommercial-ShareAlike License, which means that you can reuse and modify the material only for noncommercial purposes, must attribute OpenStax, and must distribute any derivative works under the same license.
  • Any commercial printing of this textbook, including using a local or custom printer, must be approved by OpenStax, and proper citation provided.
  • OpenStax-copyrighted images, activities, assessments, and similar components of this book are subject to the same licensing – CC-BY-NC-SA. They can be used for noncommercial purposes with attribution. Commercial use requires permission.
  • Permission requests: Anyone who intends to incorporate this content (including text, images, and other components) into large language models, use it in AI offerings, use it commercially (including in print), and/or has questions about another use case is welcome to complete our reuse request form.
Attribution information
  • If you are redistributing all or part of this book in a noncommercial print format, then you must include on every physical page the following attribution:

    Access for free at https://openstax.org/books/biology-2e/pages/1-introduction

  • If you are redistributing all or part of this book in a noncommercial digital format, then for every page that includes OpenStax content, you must license the derivative work under the same CC-BY-NC-SA license as the original, and include on every digital page view the following attribution:

    Access for free at https://openstax.org/books/biology-2e/pages/1-introduction

Citation information

The information below includes the information needed to generate citations in most major styles (APA, MLA, etc.); you must reformat and organize the information as needed to fit the requirements of the style. Use the information below to generate a citation. We recommend using a citation tool such as this one.

© Jul 22, 2026 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike License. The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo, and Rice University name, and Rice University logo trademarks, or wordmarks are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.