Jens Christen (Christian) Clausen (March 11, 1891 – November 22, 1969) was a Danish- American botanist,

geneticist A geneticist is a biologist or physician who studies genetics, the science of genes, heredity, and variation of organisms. A geneticist can be employed as a scientist or a lecturer. Geneticists may perform general research on genetic processes ...

, and ecologist. He is considered a pioneer in the field of ecological and evolutionary genetics of plants.

Biography

Clausen was born in Nr. Eskilstrup, Soderup parish on the island of

Zealand Zealand ( da, Sjælland ) at 7,031 km2 is the largest and most populous island in Denmark proper (thus excluding Greenland and Disko Island, which are larger in size). Zealand had a population of 2,319,705 on 1 January 2020. It is th ...

, Denmark. He was the son of Christen Augustinus Clausen (1858-1938) and Christine (Christensen) Clausen (1856-1933). His parents were farmers and at age 14 he took responsibility for the family farm and was largely educated at home with the assistance of a local school teacher. He studied Mendel's genetics and Darwinian evolutionary theory. In 1913 he entered the

University of Copenhagen The University of Copenhagen ( da, Københavns Universitet, KU) is a prestigious public university, public research university in Copenhagen, Copenhagen, Denmark. Founded in 1479, the University of Copenhagen is the second-oldest university in ...

, where he studied

botany Botany, also called plant science (or plant sciences), plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytologist is a scientist who specialises in this field. The term "bot ...

genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar worki ...

and

ecology Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overl ...

Christen Raunkiær To christen is to perform the religious act of baptism. Christen may also refer to: People Surname * Adolf Christen (1811–1883), court actor, theater director and theater manager * Andreas Christen (born 1989), footballer from Liechtenstein * ...

suggested he undertake graduate studies and Clausen chose to study the genetics and ecology of the plant family

Violaceae Violaceae is a family of flowering plants established in 1802, consisting of about 1000 species in about 25 genera. It takes its name from the genus ''Viola'', the violets and pansies. Older classifications such as the Cronquist system placed ...

. He studied hybridization patterns across a range of environments and described

introgression Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Intro ...

of genes between species. He completed his master's degree in 1920 and was appointed assistant professor to geneticist Øjvind Winge at the Royal Veterinary and Agricultural University in Copenhagen. In 1926, Clausen was awarded his Ph.D. for his work on Violaceae; his monograph was one of the first publications that combined systematics, ecology and genetics for any plant group. During 1927-1928, Clausen received a Rockefeller scholarship to study at the

University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...

where he worked on the genetics of the genus '' Crepis'' with E. B. Babcock. During this time he met Californian botanist

Harvey Monroe Hall Harvey Monroe Hall (March 29, 1874 – March 11, 1932) was an American botanist particularly noted for his taxonomic work in the western United States. Hall was born in Lee County, Illinois, on March 29, 1874, and raised near Riverside, California ...

, who invited Clausen to return to the United States to work on the ecological genetics of

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...

native species In biogeography, a native species is indigenous to a given region or ecosystem if its presence in that region is the result of only local natural evolution (though often popularised as "with no human intervention") during history. The term is equ ...

. Clausen returned to the

in 1931 as a staff member at the

Carnegie Institution of Washington The Carnegie Institution of Washington (the organization's legal name), known also for public purposes as the Carnegie Institution for Science (CIS), is an organization in the United States established to fund and perform scientific research. Th ...

Department of Plant Biology at

Stanford, California Stanford is a census-designated place (CDP) in the northwest corner of Santa Clara County, California, United States. It is the home of Stanford University. The population was 21,150 at the 2020 census. Stanford is an unincorporated area of ...

. He would become a naturalized citizen of the United States during 1943. With

taxonomist In biology, taxonomy () is the scientific study of naming, defining ( circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given ...

David D. Keck David Daniels Keck (October 24, 1903 – March 10, 1995) was an American botanist who was notable for his work on angiosperm taxonomy and genetics. Keck was born in Omaha, Nebraska. He completed undergraduate studies at Pomona College in 1925 ...

and physiologist

William Hiesey William McKinley Hiesey (August 21, 1903 – August 7, 1998) was an American botanist who specialized in ecological physiology. He was notable for his collaboration with Jens Clausen and David D. Keck at Stanford University Stanford Univers ...

, he formed the first interdisciplinary effort to combine

and

systematics Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: cladograms, phylogenetic t ...

in order to understand the ecological genetics of the

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

ary process in

plants. The project lasted 20 years during which they performed some of the classic experiments in

plant ecology Plant ecology is a subdiscipline of ecology which studies the distribution and abundance of plants, the effects of environmental factors upon the abundance of plants, and the interactions among and between plants and other organisms. Examples ...

in which they looked at species formation across

Altitudinal zonation Altitudinal zonation (or elevational zonation) in mountainous regions describes the natural layering of ecosystems that occurs at distinct elevations due to varying environmental conditions. Temperature, humidity, soil composition, and solar radi ...

using experimental plots at Stanford (near sea level), at Mather near

Yosemite National Park Yosemite National Park ( ) is an American national park in California, surrounded on the southeast by Sierra National Forest and on the northwest by Stanislaus National Forest. The park is managed by the National Park Service and covers an ...

(at about 4,600 feet), and at Timberline in the

Sierra Nevada The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primari ...

(at about 10,000 feet).

Works

Collectively Clausen, Keck and Hiesey wrote five books on their work, including ''Experimental Studies on the Nature of Species. I. Effect of Varied Environments on Western North American Plants'' published in 1940 and ''Experimental Studies on the Nature of Species. III. Environmental Responses of Climatic Races of

Achillea ''Achillea'' is a genus of flowering plants in the family Asteraceae, known colloquially as yarrows. The plants typically have frilly leaves. The common name "yarrow" usually refers to '' A. millefolium''. The genus was named after the G ...

'' in 1948. Clausen produced one additional book about his work based on the

Messenger Lectures The Messenger Lectures are a series of talks given by scholars and public figures at Cornell University. They were founded in 1924 by a gift from Hiram Messenger of "a fund to provide a course of lectures on the Evolution of Civilization for the s ...

he gave at

Cornell Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to teac ...

which was published in 1951 as ''Stages in the Evolution of Plant Species''.

Honors

Clausen was elected a member of the

National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the Nat ...

, the

American Academy of Arts and Sciences The American Academy of Arts and Sciences (abbreviation: AAA&S) is one of the oldest learned societies in the United States. It was founded in 1780 during the American Revolution by John Adams, John Hancock, James Bowdoin, Andrew Oliver, ...

, and the Royal Swedish Academy of Sciences; he was also a member of the

Botanical Society of America The Botanical Society of America (BSA) represents professional and amateur botanists, researchers, educators and students in over 80 countries of the world. It functions as a United States nonprofit 501(c)(3) membership society. History The s ...

, and the

Society for the Study of Evolution The Society for the Study of Evolution is a professional organization of evolutionary biologists. It was formed in the United States in 1946 to promote evolution and the integration of various fields of science concerned with evolution and to orga ...

. He was a fellow of the California Academy of Sciences and of the American Association for the Advancement of Science. He was knighted in the Order of the Danneborg by

Frederick IX of Denmark Frederick IX ( da, Christian Frederik Franz Michael Carl Valdemar Georg; 11 March 1899 – 14 January 1972) was King of Denmark from 1947 to 1972. Born into the House of Glücksburg, Frederick was the elder son of King Christian X and Quee ...

. Clausen was a member of the First Baptist Church of

Palo Alto, California Palo Alto (; Spanish for "tall stick") is a charter city in the northwestern corner of Santa Clara County, California, United States, in the San Francisco Bay Area, named after a coastal redwood tree known as El Palo Alto. The city was ...

Family

Clausen was married to Anna Hansen. Anna supported and assisted with Clausen's scientific career by undertaking "artificial pollinations, back-crossings, fixations, baggings and harvesting" of plants, as well as assisting with the recording and numbering of segregated types, thus providing material and data upon which some of his scientific writings were based.

References

Other sources

*Smocovitis, V. B. (2000) ''Clausen, Jens Christen'' in "American National Biography Online" (Oxford University Press)

External links

National Academy of Sciences Biographical Memoir
{{DEFAULTSORT:Clausen, Jens 1891 births 1969 deaths Evolutionary biologists University of California, Berkeley alumni University of Copenhagen alumni Members of the Royal Swedish Academy of Sciences Danish emigrants to the United States 20th-century Danish botanists Danish geneticists American geneticists Order of the Dannebrog Members of the United States National Academy of Sciences People from Guldborgsund Municipality