Jordan's rule (sense 1) is an

ecogeographical rule A biological rule or biological law is a generalized law, principle, or rule of thumb formulated to describe patterns observed in living organisms. Biological rules and laws are often developed as succinct, broadly applicable ways to explain comp ...

that describes the

inverse relationship In statistics, there is a negative relationship or inverse relationship between two variables if higher values of one variable tend to be associated with lower values of the other. A negative relationship between two variables usually implies that ...

between water temperature and

meristic Meristics is an area of ichthyology and herpetology which relates to counting quantitative features of fish and Reptile, reptiles, such as the number of fins or scales. A meristic (countable trait) can be used to describe a particular species of fi ...

characteristics in various species of

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

. The most commonly observed relationship is that

fin ray Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as see ...

vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic i ...

, or scale numbers increase with decreasing temperature. The rule is named after

David Starr Jordan David Starr Jordan (January 19, 1851 – September 19, 1931) was the founding president of Stanford University, serving from 1891 to 1913. He was an ichthyologist during his research career. Prior to serving as president of Stanford Univer ...

(1851–1931), the father of American

ichthyology Ichthyology is the branch of zoology devoted to the study of fish, including bony fish ( Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). According to FishBase, 33,400 species of fish had been described as of Octob ...

. Jordan's law (or rule) (sense 2) is also an ecogeographical rule (named after the same scientist) that states: "‘ ven any species in any region, the nearest related species is not likely to be found in the same region nor in a remote region, but in a neighbouring district separated from the first by a barrier of some sort’ This "rule" is frequently violated (see discussion in Fitzpatrick & Turelli 2007), but when patterns are consistent with Jordan's rule (sense 2), this suggests an important role for

allopatric speciation Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

in the diversification of the

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

in question. Jordan himself wrote: "To this generalization Dr.

Allen Allen, Allen's or Allens may refer to: Buildings * Allen Arena, an indoor arena at Lipscomb University in Nashville, Tennessee * Allen Center, a skyscraper complex in downtown Houston, Texas * Allen Fieldhouse, an indoor sports arena on the Univer ...

, in a late number of Science, gives the name of 'Jordan's Law.' The present writer makes no claim to the discovery of this law. The language above quoted is his, but the idea is familiar to all students of geographical distribution and goes back to the master in that field,

Moritz Wagner Moritz Wagner may refer to: * Moritz Wagner (basketball) (born 1997), German professional basketball player * Moritz Wagner (naturalist) Moritz Wagner (Bayreuth, 3 October 1813 – Munich, 31 May 1887) was a German explorer, collector, geographer ...

." Thus, Jordan's law is an example of

Stigler's law Stigler's law of eponymy, proposed by University of Chicago statistics professor Stephen Stigler in his 1980 publication ''Stigler’s law of eponymy'', states that no scientific discovery is named after its original discoverer. Examples include ...

References

{{Biological rules Ecogeographic rules Ichthyology

See also

References