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 process ...

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

Biography

Clausen was born in Nr.

Eskilstrup Eskilstrup is a town some north of Nykøbing Falster on the Danish island of Falster. As of 2024, it had a population of 1,082. History Eskilstrup Church, built in the Romanesque style, dates from the 12th century. In accordance with local t ...

, Soderup parish on the island of

Zealand Zealand ( ) is the largest and most populous islands of Denmark, island in Denmark proper (thus excluding Greenland and Disko Island, which are larger in size) at 7,031 km2 (2715 sq. mi.). Zealand had a population of 2,319,705 on 1 Januar ...

, 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 (, KU) is a public university, public research university in Copenhagen, Copenhagen, Denmark. Founded in 1479, the University of Copenhagen is the second-oldest university in Scandinavia, after Uppsala University. ...

, where he studied

botany Botany, also called plant science, is the branch of natural science and biology studying plants, especially Plant anatomy, their anatomy, Plant taxonomy, taxonomy, and Plant ecology, ecology. A botanist or plant scientist is a scientist who s ...

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 Augustinians, Augustinian ...

and

ecology Ecology () is the natural science of the relationships among living organisms and their Natural environment, environment. Ecology considers organisms at the individual, population, community (ecology), community, ecosystem, and biosphere lev ...

. Christen Raunkiær 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 plac ...

. 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. Introg ...

of genes between species. He completed his master's degree in 1920 and was appointed assistant professor to geneticist

Øjvind Winge Øjvind Winge (19 May 1886 – 5 April 1964) was a Danish biologist and a pioneer in yeast genetics. Education Winge was born in the city of Aarhus in Jutland, the mainland of Denmark. After completing secondary school he travelled to the Univer ...

at the

Royal Veterinary and Agricultural University The Royal Veterinary and Agricultural University (, abbr. KVL, , abbr. RVA) was a veterinary and agricultural science university in Denmark. It was founded in 1856 and operated until 2007, when it became a part of the University of Copenhagen. It ...

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 university, public Land-grant university, land-grant research university in Berkeley, California, United States. Founded in 1868 and named after t ...

where he worked on the genetics of the genus '' Crepis'' with E. B. Babcock. During this time he met Californian botanist Harvey Monroe Hall, who invited Clausen to return to the United States to work on the

ecological genetics Ecological genetics is the study of genetics in natural populations. It combines ecology, evolution, and genetics to understand the processes behind adaptation. It is virtually synonymous with the field of molecular ecology. This contrasts wit ...

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

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 equi ...

. Clausen returned to the

in 1931 as a staff member at the

Carnegie Institution of Washington The Carnegie Institution for Science, also known as Carnegie Science and the Carnegie Institution of Washington, is an organization established to fund and perform scientific research in the United States. This institution is headquartered in W ...

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, after which it was named. The CDP's population was 21,150 at the United States Census, ...

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

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

David D. Keck and physiologist William Hiesey, he formed the first interdisciplinary effort to combine

and

systematics 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: phylogenetic trees, phylogenies). Phy ...

in order to understand the

of the

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

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 that studies the distribution and abundance (ecology), abundance of plants, the effects of environmental factors upon the abundance of plants, and the interactions among plants and between plants and ...

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 a List of national parks of the United States, national park of the United States in California. It is bordered on the southeast by Sierra National Forest and on the northwest by Stanislaus National Forest. The p ...

(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. The plants typically have frilly leaves and are known colloquially as yarrows, although this common name usually refers to '' A. millefolium''. The genus was named after ...

'' in 1948. Clausen produced one additional book about his work based on the Messenger Lectures he gave at Cornell 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, NGO, 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 ...

, the

American Academy of Arts and Sciences The American Academy of Arts and Sciences (The Academy) 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 other ...

, and the

Royal Swedish Academy of Sciences The Royal Swedish Academy of Sciences () is one of the Swedish Royal Academies, royal academies of Sweden. Founded on 2 June 1739, it is an independent, non-governmental scientific organization that takes special responsibility for promoting nat ...

; he was also a member of the Botanical Society of America, 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 the study of evolution and the integration of various fields of science concerned with evolution ...

. 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 The Order of the Dannebrog () is a Danish order of chivalry instituted in 1671 by Christian V. Until 1808, membership in the Order was limited to fifty members of noble or royal rank, who formed a single class known as ''White Knights'' t ...

Frederik IX of Denmark Frederik IX (Christian Frederik Franz Michael Carl Valdemar Georg; 11 March 1899 – 14 January 1972) was King of Denmark from 1947 to 1972. Frederik was born into the House of Glücksburg during the reign of his great-grandfather King Chr ...

. Clausen was a member of the First Baptist Church of

Palo Alto, California Palo Alto ( ; Spanish language, Spanish for ) is a charter city in northwestern Santa Clara County, California, United States, in the San Francisco Bay Area, named after a Sequoia sempervirens, coastal redwood tree known as El Palo Alto. Th ...

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 American 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