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Scientific names of species

The scientific name of a species is one of the most important pieces of information that can be published about the species. It doesn't necessarily say a lot about the species by itself. But it is (normally) a globally-recognised way of identifying that species, and so provides the key to obtaining everything already published about the species.

Scientific names

Scientific names are also known as "species names" and "latin names".

A species is, approximately, a reproducing population, hence a gene-pool. (Homo sapiens, human beings, are such a population, and the superficial differences across the planet, such as skin colour or the propensity to fat buttocks, are irrelevant at the species level. We can all breed with one-another, and often do. But these differences are interesting to a photographer!)

Classifying all of the life that there has ever been on the planet is a massive task. It is done by using a hierarchic system, so that people can focus on the subset of interest, such as "all animals", or "all birds", or a subspecies of the sea lions found on the west coast of the Americas such as "Galapagos Sea Lion". The hierarchy includes: Kingdom, Phylum, Class, Order, Family, Genus, Species. So human beings are: Kingdom Animalia; Phylum Chordata; Class Mammalia; Order Primates; Family Hominidae; Genus & Species Homo sapiens. The Genus & Species name, such as Homo sapiens, is unique by itself, and is sometimes simply called the species name or species. (The last name, such as sapiens, is often duplicated, and is pretty well meaningless by itself). Sometimes a subspecies name follows.

Tits and Ass ... and Sally Lightfoot

Here are some cautionary tales about the relationship (or lack of it) between commonly-used names and scientific names for birds and animals.

  • Coal Tit, taken in my gardenIn the UK at least, what some people call "true tits" belong to the genus Parus. (Coal Tit: Parus ater; etc). But other species of bird called "tit" belong to other genera, and indeed to different families. (Long-tailed Tit: Aegithalos caudatus; etc). "Tit" originally meant a small bird, and so the name lacks scientific precision.
  • "Asses" are neither a genus nor a species, but in fact a subgenus Asinus (of genus Equus - Horse). So they are a set of species, presumably descended from a single species a long time ago. Perhaps if there is someone still classifying species millions of years in the future, Asinus will have become a genus in its own right as a result of continuing speciation resulting from natural selection.
  • Sally Lightfoot Crab"Sally Lightfoot" is a name given to 2 (at least) totally different species of crab. The species in the Galapagos Islands is Grapsus grapsus, while in the Caribbean there is Percnon gibbesi, and also Percnon planissimum. (I don't know how this ambiguity arose, but I would like more information on the topic. It is often claimed that the name arose from a 19th century Caribbean dancer called Sally).

Hence the need for scientific names. The photographs on this web site are accompanied by scientific names, often based on the opinions of experts. Unfortunately, it is likely that perhaps 1% or more of these names are inaccurate. Please tell us of errors, but also supply evidence to give us confidence.

What does the species hierarchy mean?

Consider Human Beings, a couple of types of Tit, and the Sally Lightfoot Crab. Here are their full scientific names.









Human Being

Animalia Chordata Mammalia Primates Hominidae Homo sapiens

Coal Tit

    Aves Passeriformes Paridae Parus ater

Long-tailed Tit

        Aegithalidae Aegithalos caudatus

Sally Lightfoot Crab (Galapagos Island version)

  Arthropoda Malacostraca Decapoda Grapsidae Grapsus grapsus

The non-evolutionary view is perhaps that this is simply a way of classifying creatures according to common characteristics. By this definition, it could be arbitrary.

The evolutionary view is that this is a story of part of the last billion years of life on Earth. Sometime before the Cambrian Period, perhaps during the the Vendian Period, there was presumably a reproducing population, equivalent to a species, that is the common ancestor of the entire "Animal" kingdom.

That "Animal" species, for various reasons, separated into a number of other species. So it was no longer a species - it was now perhaps what we would call a Genus of lots species. Just one of those species had a "notochord", running along the body, and carrying nerves - "Chordata". Birds and mammals descended from this species, while crabs didn't.

This "Chordata" species eventually itself separated into a number of species, and so "Chordata" became a Genus, pushing the original "Animalia" up yet another level. Now the ancestors of birds and animals became different species. (While "Arthropods" continued their independent way). One species developed milk and hair and special ear-bones, becoming "Mammalia", while the other developed feathers, becoming "Aves". And there were many others besides. (This shows that "Birds and Animals" is not a good name for a web site!)

And so on. What appeared to be species for perhaps many millions of years eventually separated into multiple species, each time adding a new level to the hierarchy. So the hierarchy is (hopefully) a history of common ancestors, not just an arbitrary classification system.

The hierarchy is still somewhat arbitrary. There is no clear definition about how many levels it should have. Sometimes in the literature there will appear a "sub-phylum" or a "tribe". There are a lot of ancestral species in half a billion years!

Page last updated: 8 January, 2010