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. He is best known for his theories of "catastrophic selection" and "saltational speciation", which are closely aligned with the concepts of quantum evolution and sympatric speciation. The concepts were first articulated in 1958 by Lewis and Peter H. Raven, and later refined in a 1962 paper by Lewis in which he coined the term "catastrophic selection". In 1966, he referred to the same mechanism as "saltational speciation".
Lewis was Dean of Life Sciences at the University of California, Los Angeles from 1962 to 1981, a Fellow of the American Association for the Advancement of Science (1955), recipient of a Guggenheim Fellowship (1955), president of the Pacific Division of the Botanical Society of America (1959), president of the Society for the Study of Evolution (1961), president of the American Society of Plant Taxonomists (1969), president of the International Organization of Plant Biosystematics (1969–1975), and president of the American Society of Naturalists (1971), as well as a Fellow of the California Academy of Sciences. In 2006, he became the Dickson Emeritus Professor of the Year at UCLA.
Early life Lewis grew up on a ranch in Redlands, California, where his father grew apricots and oranges. His interest in plants dates at least from the age of 10 when his fifth grade teacher taught the class how to press flowers. His junior high and Redlands High School teachers continued to encourage his interest in plants. When he was in 10th grade he got permission to take a class in botany usually restricted to 11th and 12th graders. 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. He became president of the society in about 1939. During this time he attended a Botanical Society of America meeting, where he met Willis Linn Jepson.
Education Harlan Lewis graduated from Redlands High School in 1937, and got an A.A. degree in 1939 from San Bernardino Valley College.
He transferred to UCLA in 1939 as a junior. He started work with Carl Epling as an undergraduate, and published a paper with him in 1940 as the first author on the distributions of three species pairs in Californian chaparral and coastal sage plant communities. He continued with Epling as a graduate student, and got his M.A. in 1942 working on the genus Trichostema in the family Lamiaceae. His Ph.D. work concerned diploid and tetraploid Californian species of Delphinium. WWII interrupted his studies, and he completed his thesis in 1946.
Lewis became a faculty member at UCLA in that same year, 1946.
Military He joined the United States Army Air Corps at the start of WWII, working at Caltech with Frits Warmolt Went on camouflage.
Research
Harlan Lewis' research interests were far ranging. They included taxonomy, cytogenetics, systematics, genetics, evolution, plant distributions, and even physiological ecology. And all of these manifested themselves before 1950. Indeed, as a young scientist he was involved with many research topics. His first publication was with Carl Epling in 1940 covered the distributions of three species pairs in Californian chaparral and coastal sage scrub communities. In this paper he shows his first interest in plant distributions as they relate to speciation. His next publications with Epling followed in 1942. One was taxonomic in nature, a continuing interest of his, and concerned itself with the genus Monarda in the Lamiaceae. His second paper in 1942 concerned itself with the distributions of the chaparral and coastal sage scrub communities in cis-montane California, and they concluded that these two communities had their centers of distribution in San Diego County, and probably entered the Southwestern United States from the North American Plateau. He also received his M.A. degree in 1942 on a completely different subject: the taxonomy of Trichostema in the Lamiaceae, which was published in 1945. As a result of his work with Frits Went at California Institute of Technology during the WWII years he published on yet a different subject: that of the response of 13 California annuals to photoperiod and temperature. Although they were not able to correlate the plant's response under artificial conditions to nature, they did discover that Madia elegans was inhibited in flowering by intermediate day lengths, and was induced to flowering by either short or long days, a rare condition known as ambiphotoperiodism. His PhD work in Delphinium was reported in an abstract in 1946, titled "Polyploidy in the Californian Delphiniums"; here he showed his first interest in the effects of ploidy on adaptation on three species that consisted of races that were diploid and tetraploid, and found that there were no morphological or ecological differences between the diploids and tetraploids. In 1947 he published on problems associated with using leaves for taxonomic purposes in Delphinium.
Clarkia 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. This suggestion by Stebbins was prophetic as Ford and Gottlieb estimated that as of 2003 there were more than 200 publications on Clarkia.
For the rest of Lewis' career he devoted most of his energies to the genetics, taxonomy, and speciation of plants in the genus. In 1947 he was awarded a one-year postdoctoral fellowship to the John Innes Horticultural Institution in England with Kenneth Mather. While there he worked on the cytogenetics of Clarkia, and published on chromosomal counts in Clarkia in their Annual Report. It was not until 1951 that he published his next paper in Clarkia, which was concerned with the widespread occurrence of supernumerary chromosomes in Clarkia elegans, now known as Clarkia unguiculata. He further noted that members of this species were heterozygous for one or more reciprocal translocations, and that these abnormalities had no genetic effect. However, he hypothesized that the supernumeraries were produced as by-products of translocation heterozygotes, and that the mechanisms producing supernumerary chromosomes could account for the "various chromosome numbers found in this genus."
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 paper described a new species, C. similis, which he hypothesized was a tetraploid between C. modesta and C. epilobioides; all of which were morphologically very similar. Another paper was a taxonomic study that changed some of the nomenclature in Clarkia, combining species of Clarkia with Godetia, and adding four new species. 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 second new species was C. affinis, an allohexaploid closely related to C. purpurea, an allohexaploid. A third new species was C. prostrata, an allohexapoid closely resembling C. davyi, a tetraploid. The fourth new species was C. imbricata, which was very similar to C. williamsonii.
The third 1953 paper discussed the relationship between changes in the basic chromosome number of Clarkia with Californian habitats. Specifically, he found that increased basal chromosomal numbers in diploid Clarkia were correlated with a xeric habitat, and hypothesized that the genus may have originated at the more mesic ecotone between the Arcto-Tertiary and Madro-Tertiary Floras and spread to more xeric habitats. His fourth paper in 1953 established what he hypothesized to be the primary mode of speciation in Clarkia: Speciation in Clarkia...has probably resulted from a combination of a variety of factors. Of these perhaps the most important has been the differential accumulation in different populations of adapted gene combinations associated with particular chromosome rearrangements. 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.
In 1954 he published on yet another new species, C. exilis, which was morphologically very similar to C. unguiculata. In this paper he states: Several new species of Clarkia have recently been described which have a very restricted distribution and which are morphologically very similar to well known and widely ranging species...These sympatric species pairs offer an unusual opportunity for study of species differentiation.
1955 marked the publication of a complete taxonomic revision of the Genus Clarkia. This was followed by an analysis of three subspecies of Clarkia biloba, which ranged mostly from north to south along the Sierran foothills: ssp. brandegeae being northernmost, more central ssp. biloba, with ssp. australis being southernmost; their primary morphological difference being petal color and shape as well as leaf morphology. The fertility amongst the hybrids was high, except that the northern ssp. brandegeae was the least fertile with the other two, probably caused by a chromosomal rearrangement; it was observed that ssp. brandegeae was also morphologically similar to C. dudleyana. The authors concluded that subspeciation in C. biloba did not follow patterns seen in other plants, but was more disjunct involving "barriers to gene exchange due to spacing of the colonies, supplemented in the northern subspecies by a factor which reduces fertility in heterozygotes." This work was then followed by the now famous publication on Clarkia lingulata in 1956 with M. Roberts. C. lingulata is a "sister species" of Clarkia biloba ssp. australis, morphologically almost identical to each other except that C. lingulata does not have notch in its petals, has a low interspecific fertility, and they differ from each other by a translocation, a paracentric inversion, and one additional chromosome; C. lingulata grows at the southernmost extent of ssp. australis range. They concluded that C. lingulata evolved rapidly and recently from C. biloba:In any event, the transition from one species to the other seems to have been a rapid process which depended only upon the fixation of one or perhaps two chromosomal alterations, which also led to a morphological and perhaps ecological difference. 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. The close relationship of the genomes of C. lingulata and australis, the geographical juxtaposition the two taxa, and the restricted distribution of the former, suggests to us not only a rapid but also a relatively recent origin of C. lingulata from C. biloba australis.
In 1950 Peter H. Raven, at the age of 14, had collected a plant called C. rubicunda. In the course of Harlan and his wife Margaret revising the genus Clarkia they discovered the herbarium specimen collected by Raven. They visited him in 1952 when he was 16, and wanted to know where the collection was made. In 1958 Lewis and Raven published a botanical description of this plant, called C. franciscana, which was morphologically very closely related to C. rubicunda and C. amoena.