Definition
What is a species?
A species is the basic unit that biologists use to name and count living things, and the level at which new branches on the tree of life split off. The most widely taught version, the biological species concept, defines a species as a set of populations whose members do or could interbreed in nature and produce offspring that are themselves fertile. Members share one gene pool, so new gene variants can spread among them, while barriers to reproduction keep that pool apart from those of other species.
Appearance can mislead. Dog breeds differ hugely in size and shape yet belong to one species, while some birds that look almost identical never mate with each other and count as separate species. A horse and a donkey can produce a mule, but because mules are almost always sterile, horses and donkeys remain distinct species.
The biological definition has limits. It cannot be applied to bacteria and other organisms that reproduce asexually, or to fossils, and some plants and animals hybridize freely across apparent species lines. Biologists therefore also use species concepts based on shared ancestry, body form or DNA. Each species receives a two-part scientific name, such as Homo sapiens, and new species arise through speciation.
Word parts
Where does the word “species” come from?
- speci-
- appearance, kindLatin species, from specere, to look
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Terms that go with it
- SpeciationSpeciation is the evolutionary process in which one ancestral species splits into two or more species whose members can no longer interbreed.
- Binomial nomenclatureBinomial nomenclature is the system of naming each species with two Latin-form words, a genus name followed by a specific epithet, as in Homo sapiens.
- TaxonomyIn biology, taxonomy is the science of describing, naming and classifying organisms into a nested hierarchy of groups such as genus, family and order.
- Gene flowGene flow is the movement of alleles from one population into another when individuals or their gametes migrate and then breed.
- PopulationIn ecology, a population is all the individuals of one species that live in the same area at the same time and can breed with one another.
- Natural selectionNatural selection is the process by which inherited traits that improve survival and reproduction become more common in a population over generations.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Biology 2e, 18.2 Formation of New Species
- Understanding Evolution (UC Museum of Paleontology): Defining a species
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