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Understanding Evolution

Understanding Evolution

Your one-stop source for information on evolution

Understanding Evolution

  • Home
  • Evolution 101
    • An introduction to evolution: what is evolution and how does it work?
      • 1_historyoflife_menu_iconThe history of life: looking at the patterns – Change over time and shared ancestors
      • 2_mechanisms_menu_iconMechanisms: the processes of evolution – Selection, mutation, migration, and more
      • 3_microevo_menu_iconMicroevolution – Evolution within a population
      • 4_speciation_menu_iconSpeciation – How new species arise
      • 5_macroevo_menu_iconMacroevolution – Evolution above the species level
      • 6_bigissues_menu_iconThe big issues – Pacing, diversity, complexity, and trends
  • Teach Evolution
    • Lessons and teaching tools
      • Teaching Resources
      • Image Library
      • Using research profiles with students
      • Active-learning slides for instruction
      • Using Evo in the News with students
      • Guide to Evo 101 and Digging Data
    • Conceptual framework
      • Alignment with the Next Generation Science Standards
      • teach-evo-menu-icon
    • Teaching guides
      • K-2 teaching guide
      • 3-5 teaching guide
      • 6-8 teaching guide
      • 9-12 teaching guide
      • Undergraduate teaching guide

    • Misconceptions about evolution

    • Dealing with objections to evolution
      • Information on controversies in the public arena relating to evolution
  • Learn Evolution
Home → C

C

clicker question

Posted October 13, 2021

an active learning technique in which an instructor uses a classroom response system to instantly guage student responses to multiple choice questions. Classroom response systems can be simulated by having students hold up differently colored pieces of paper to indicate different answers.

crustacean

Posted July 3, 2020

Crustaceans are a group of arthropods distinguished by the following characters:

  • a body divided into cephalothorax and abdomen

  • two pairs of antennae and three pairs of mouth appendages

Examples of crustaceans include crabs, pillbugs, and barnacles (It’s true! Under that lumpy exterior, barnacles are crustaceans with all of the right characters!).

Sally Lightfoot Crab photo by Gerald and Buff Corsi © California Academy of Sciences; Acorn Barnacles photo by Sherry Ballard © California Academy of Sciences; Pillbugs photo © 2002 William Leonard

cosmic dust

Posted July 3, 2020

Small particles or grains of solid material in space. Cosmic dust forms in outflows and winds from stars or supernovae and is rich in the heavy elements and organic compounds necessary for life. Dust from early generations of stars mixed with gas in nebulae and ultimately formed subsequent stars and planetary systems.

coprolite

Posted July 3, 2020

Fossilized dung.

constraint

Posted July 3, 2020

In terms of evolution, an aspect of a lineage’s genetic makeup that prevents the lineage from reaching a particular, potentially advantageous evolutionary outcome (e.g., an organism’s developmental process prevents the evolution of a trait that would allow a lineage to invade a new habitat).

comet

Posted July 3, 2020

An asteroid-like object containing ice and other compounds such as methane and ammonia. When heated by the Sun, a comet develops a surrounding cloud of gas called a “coma” and often a visible tail.

coevolution

Posted July 3, 2020

A process in which two or more different species reciprocally effect each other’s evolution. For example, species A evolves, which causes species B to evolve, which causes species A to evolve, which causes species B to evolve, etc. For a more detailed explanation, see our resource on coevolution in Evolution 101.

codon

Posted July 3, 2020

A three base unit of DNA that specifies an amino acid or the end of a protein.

chromosome

Posted July 3, 2020

A cellular structure made of DNA and proteins that contains all or part of an organism’s heritable, genetic information. Humans have 23 pairs of chromosomes.

chromosomal inversion

Posted July 3, 2020

A mutation in which a section of chromosome is reversed 180 degrees. Because inversions in certain chromosomes can be observed with a light microscope, they were particularly important in early genetic studies.

chloroplast

Posted July 3, 2020

In plants and photosynthetic protists, a cellular body that uses energy from the sun (sunlight) to create organic compounds from carbon dioxide and water.

chitin

Posted July 3, 2020

Hard, tough substance that occurs widely in nature, particularly in the exoskeletons of arthropods. Chemically, chitin is a carbohydrate and is made from sugar molecules.

chelicerate

Posted July 3, 2020

Chelicerates are a group of arthropods distinguished by the following characters:

  • a body divided into a cephalothorax and abdomen

  • no antennae, but two pairs of appendages on the anterior cephalothorax (chelicerae and pedipalps), and four pairs of walking legs

Examples of chelicerates include spiders, scorpions, and horseshoe crabs.

Black Widow Spider photo by George W. Robinson © California Academy of Sciences; Scorpion photo by Dr. Antonio J. Ferreira © California Academy of Sciences; Horseshoe Crab photo © 2000 John White

carnivore

Posted July 3, 2020

An organism that eats almost exclusively animals (caro = flesh, vorare = to swallow up).

carbon chauvinism

Posted July 3, 2020

A suggestion by astronomer Carl Sagan that it is narrow-minded to view carbon as the only possible basis for life. He proposed that life in other places might be based on alternative biochemistries not found on Earth.

Cambrian Period

Posted July 3, 2020

Geologic time period 543-490 million years ago. The Cambrian is the first period of the Paleozoic era, during which all animals and plants lived in the Earth’s oceans. Many organisms that we recognize as members of modern animal groups (including the arthropods, sponges, chordates, and molluscs) made their first unmistakable appearance in the fossil record during the Cambrian.

chordates

Posted July 3, 2020

Any member of the animal clade Chordata, a large group of vertebrates and some marine invertebrates. Chordates have a notochord, a rod-like cartilaginous structure supporting the nerve cord, that they inherited from their common ancestor. Modern chordates include vertebrates, tunicates, hagfish, and lancelets.

clade

Posted July 3, 2020

A group of organisms that includes all the descendents of a common ancestor and that ancestor. For example, birds, dinosaurs, crocodiles and their extinct relatives form a clade. For a more detailed explanation, see our resource on clades in Evolution 101.

common ancestor

Posted July 3, 2020

Ancestral organism shared by two or more descendent lineages — in other words, an ancestor that they have in common. For example, the common ancestors of two biological siblings include their parents and grandparents; the common ancestors of a coyote and a wolf include the first canine and the first mammal.

character

Posted July 3, 2020

A recognizable feature of an organism. Characters may be morphological, behavioral, physiological, or molecular. They are used to reconstruct phylogenies.

convergent evolution

Posted July 3, 2020

Process in which two distinct lineages evolve a similar characteristic independently of one another. This often occurs because both lineages face similar environmental challenges and selective pressures.

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