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2.3: Evolution

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    Evolution means (in general usage) the gradual development of something, especially from simple to more complex forms. In biological sciences, evolution involves the processes by which different kinds of living organisms are thought to have developed and diversified from earlier forms during the history of the Earth.

    Biological evolution also involves changes in heritable genetic traits within biological populations over successive generations (first described by Gregor Johann Mendel in 1865). Evolution occurs at many scales including the molecular level, cell level, organism level, species level, and ecosystem community level.

    Evolution and classification Classification of humans
    Figure 2.6. Evolution and classification of living things (illustrated) based of shared or identifying characteristics. Figure 2.7. Human taxonomy illustrated within the hierarchical classification of living things (kingdom, phylum, class, order, family, genus, and species).
    Cat classification dog
    Figure 2.8. Classification (taxonomy) of a house cat. Figure 2.9. Classification (taxonomy) of a dog.

    Evolutionary Theory Highlights

    Evolutionary theory is a an essential component of the knowledge supporting the current geologic time scale.
    • Evolution supports an old earth (~4.56 billion years).
    • The different time periods represented on the geologic time scale have uniquely defined populations of fossil species representative of those ages.

    Natural selection (Darwinism): The strongest and best adapted organisms survive and produce offspring.

    Divergent Evolution
    • Populations that are separated environmentally can develop different features based upon an adaptation to their environment.
    • One group of organisms can radiate (or diversify) into many different groups and species.
    • Divergence leads to different and distinct populations and communities of organisms.

    Convergent Evolution
    Populations can develop similar features based upon a utilizing a similar environment and living habits. The term niche is used in biology to define an organism's role in an ecosystem.

    Examples of Convergent Evolution:
    • Both fish and marine mammals developed streamline bodies to swim efficiently.
    • Marine mammals developed fur/thick blubber to protect them from cold waters.
    Modern marine mammals share many of the same physical traits and life habits that ancient marine reptiles had before their disappearance from a mass-extinction event at the end of the Cretaceous Period (about 66 million years ago; discussed below).
    Birds, bats, flying squirrels, insects, and flying fish all independently developed means in order to take flight.
    Marsupial mammals in Australia adapted similar characteristics of mammal elsewhere (see table to right).

    Populations that evolve in separate settings
    may develop similar traits

    Examples: (niches)

    Marsupial mammals
    in Australia


    Birthing manner







    Tasmanian wolves





    How Evolution Works

    The life mission of individuals in any species is to eat, survive, and reproduce (Figure 2.10).
    While living, individuals must deal with competition (within a population of their own species, or with other species).
    Individuals must also adapt to environmental changes (changes in living space, availability of food resources, climate changes, catastrophes, etc.).
    As time passes, species with either adapt to changing situations (and evolve), or they face die offs or extinction.

    Figure 2.10. How evolution works.

    All species have a role within an ecosystem.

    The term niche refers to the specific area inhabited by an organism. The term niche also refers to the role or function of a species within an ecosystem, involving the interrelationships of a species with all the biotic and abiotic factors affecting it. All species fill a niche, ranging from limited, small micro-environments to a distribution on a regional or even global scale in a multitude of environmental settings.

    This page titled 2.3: Evolution is shared under a not declared license and was authored, remixed, and/or curated by Miracosta Oceanography 101 (Miracosta)) via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.