Frank Harlan Lewis (January 8, 1919 – December 12, 2008) was an American botanist, geneticist, taxonomist, systematist, and evolutionist who worked primarily with plants in the genus Clarkia.

The teacher, Eva Maye Hyde, had been a student of Philip A. Munz; she also inducted him into the Samuel B. Parish Botanical Society, a group for amateur botanists in Southern California.

[5][6] Harlan Lewis graduated from Redlands High School in 1937, and got an A.A. degree in 1939 from San Bernardino Valley College.

He started work with Carl Epling as an undergraduate, and published a paper with him in 1940[7] as the first author on the distributions of three species pairs in Californian chaparral and coastal sage plant communities.

[5][6] He joined the United States Army Air Corps at the start of WWII, working at Caltech with Frits Warmolt Went on camouflage.

His first publication was with Carl Epling in 1940[7] covered the distributions of three species pairs in Californian chaparral and coastal sage scrub communities.

[13] In 1946 Lewis was introduced to the annual plant Clarkia as a research subject by G. Ledyard Stebbins, who served on his Ph.D. thesis committee.

"[16] In 1953 he published four papers which may have been foundational to the rest of his Clarkia career: he not only identified new species-pairs that were morphologically very similar, but he hypothesized a mode of speciation that would account for their origin.

One of the new species was the now famous Clarkia lingulata which was observed to be closely related to C. biloba (this paper was also apparently the first that included his wife as a co-author, a team that would work together for many years).

A by-product of this accumulation of structural rearrangements has been the establishment of strong barriers to gene exchange...These phenomena both suggest that differentiation in Clarkia is often and perhaps usually a rapid process.

We are inclined to believe in the present case that the stage was set for subsequent differentiation and speciation by the single step of adding a chromosome to the genome of australis.

[24] In 1958 Lewis and Raven[25] published a botanical description of this plant, called C. franciscana, which was morphologically very closely related to C. rubicunda and C. amoena.

This pattern recurs with sufficient constancy to suggest that the various examples have a common explanation, with similar factors operating in each instance.

This pattern suggests to us a rapid shift of the adaptive mode, such as Simpson (1944) termed quantum evolution, at the diploid specific level.

The purpose of this paper is to illustrate this process by a consideration of the mode of origin of a narrow serpentine endemic, Clarkia franciscana Lewis and Raven (1958)...The repeated occurrence of the same pattern of differentiation in Clarkia suggests that a rapid reorganization of chromosomes has been an important mode of evolution in the genus.

Raven and Lewis[26] reported in 1959 that C. tenella is closely related to C. davyi, which is a tetraploid found on sea bluffs of northern and north-central California.

araucana, a tetraploid missing two chromosomes, is the newest and is the "only known example in Clarkia of a derivative occupying more mesic conditions than its progenitor."

In 1961[30] he reported that in artificially mixed populations established south of either species' range, with C. biloba being in excess, C. lingulata died out.

In 1962[2] Lewis published a more lengthy proposal for "catastrophic selection" as the primary mode of speciation in Clarkia: ...catastrophic selection in ecologically marginal populations has had a prominent role in speciation in the genus Clarkia.The following observations compellingly suggest that speciation at the diploid level in this genus ordinarily involves a rapid reorganization of the genome associated with ecological differentiation, a reorganization that involves an intermediate stage of low fertility: Closely related pairs of species bear a relationship of parent to offspring and not one of siblings.

They invariably differ by several gross structural rearrangements of the chromosomes, and sometimes by a change in basic number; as a consequence, hybrids between them are essentially sterile.

In all instances, derivative species occupy ecologically different, invariably more xeric, habitats than their progenitors.Lewis reported in 1965 on the evolution of self-pollination in Clarkia xantiana.

by reasonable extrapolation, however, it appears to be the prevalent mode of speciation in many herbaceous genera and to have had a significant role in the evolution of woody plantsIn 1968 Wedberg and Lewis reported on the distribution of widespread translocation heterozygosity and supernumerary chromosomes in C.

In a continuing interest in Clarkia phylogeny, Lewis published a paper in 1971 on species relationships using pollen grains.

His PhD work in Delphinium was reported in an abstract in 1946,[12] titled "Polyploidy in the Californian Delphiniums"; here he showed his first interest in the effects of ploidy on adaptation in three species (D. hanseni, D. gypsophilum, and D. variegatum) that consisted of races that were diploid and tetraploid, and found that there were no morphological or ecological differences between the diploids and tetraploids.

[45] They reported that its perennial habit could be put into dormancy from essentially any growth stage, and "once initiated is not broken until the following season."

Consequently, "An increase of genotypes adapted to the xeric aspects of a given site would be expected as a result of prolonged drought..." In 1959 Lewis and Epling reported on a rapid speciation event at the diploid level by hybridization.

[47] Lewis' first publication was with Carl Epling in 1940[7] which covered the distributions of three species pairs in Californian chaparral and coastal sage scrub communities.

[52] The persistence of this polymorphism over time has been a puzzle for many years, and was studied by prominent geneticists such as Sewall Wright and Theodosius Dobzhansky, going back to 1942;[53] and as recently as 2007.

Consequently, the effective "breeding group" was very large, and that any selective advantage of the flower colors "precluded significant changes in pattern during 15 seasons."

In 1964 Lewis published an extensive analysis of species in the genus Gayophytum (Onagraceae) distributed in the western U.S. and Chile.