Leigh Van Valen (August 12, 1935 – October 16, 2010) was a U.S.
evolutionary biologist.
At the time of his death, he was professor emeritus in the Department of Ecology and Evolution at the University of Chicago.
Amongst other work, Van Valen's proposed "Law of Extinction", known as Van Valen's law, drew upon the apparent constant probability (as opposed to rate) of extinction in families of related organisms, based on data compiled from existing literature on the duration of tens of thousands of genera throughout the fossil record.
Van Valen proposed the Red Queen Hypothesis (1973), as an explanatory tangent to the Law of Extinction.
The Red Queen Hypothesis captures the idea that there is a constant 'arms race' between co-evolving species.
Its name is a reference to the Red Queen's race in Lewis Carroll's Through the Looking-Glass, in which the chess board moves such that Alice must continue running just to stay in the same place.Van Valen also defined the Ecological Species Concept in 1976, in contrast to Ernst Mayr's Biological Species Concept.
In 1991, he proposed that HeLa cells be defined as a new species, which was named Helacyton gartleri.Van Valen originated the concept of fuzzy sets, prior to the formalization of this concept by L.A.
Zadeh.
He was the editor of the journal Evolutionary Theory, which he printed on simple paper stock under the motto, "Substance over form."
He had a deep understanding of many fields outside of biology, including measure theory, probability theory, logic, thermodynamics, epistemology and the philosophy of science.
As a biologist, Van Valen considered the role of zoological and botanical gardens, in a world with a degrading natural environment, to be essential for the safeguard of endangered flora and fauna.