Species, Species Concepts, and Speciation

General Ideas on Species

  • Definition of Species:

    • Species is a Latin term meaning "kind" or "appearance."
    • Formally defined, species are organisms belonging to the same kind.
    • Important to note the correct usage: "species" (plural) or "species" (singular).

  • Estimated Number of Species:

    • The exact number of species is unknown.
    • Estimates range up to 11,000,00011,000,000 species.
    • A more acceptable working estimate suggests around 15,000,00015,000,000 different kinds of organisms on the planet.

Development of the Species Concept

  • Species Fixity:

    • The concept began with the idea of species fixity.
    • Species fixity is the belief that species remain unchanged since their creation.
    • This idea originated with the teachings of Plato and his theory of forms.

  • Plato's Theory of Forms:

    • Plato proposed that there is a perfect or ideal form for all organisms.
    • Any deviation from this perfect form is considered an imperfection, not a variety or subkind.