Wilhelm Ludvig Johannsen

Wilhelm Ludvig Johannsen was born on February 3, 1857 in Copenhagen, Denmark. He was the son of a Danish Army officer, Otto Julius Georg Johannsen, and Anna Margarethe Dorthea Ebbson. He mastered many languages when he was still young and he passed his qualifying exams, but was unable to go to a university because his family lacked the means, so he was apprenticed to a pharmacist in 1872, For the next seven years he worked as a pharmacist in Denmark and Germany. In his spare time he studied chemistry and botany. In 1879 he returned to Denmark to work as a chemistry assistant in the Carlsberg laboratories where he did his own botany studies. In 1892 he became a lecturer and in 1902 he became a professor at the Copenhagen Agricultural College. In 1905 he was appointed professor of plant physiology and in 1917 he was made rector at the University of Copenhagen.

Johannsen's is best known for his genetic research. He found that there was evidence that natural selection worked in a mixed group of self-fertilizing plants but not individual self-fertilizing plants. This means that in a group of plants that produce genetically identical offspring natural selection selects for some of the plants but individual plants that produce genetically identical offspring are not effected by natural selection and the only differences in offspring are due to environmental factors. This evidence seemed contradict Charles Darwin's theory of evolution, because according to Darwin natural selection gradually changes organisms to better fit their environment. With our modern knowledge of the function of DNA in cells this result makes sense, because we know genetic variation is the result of mutation.

In addition to his research Johannesen was a prolific writer. His genetic textbooks were the most influential of their time. He coined the words "gene", "genotype" and "phenotype". Johannsen was awarded several honorary doctorates, but was appointed professor without having an academically earned doctorate. He was elected to the Danish Royal Academy of Science.

He died on November 11, 1927 in Copenhagen.


References:

Hjermitslev, Hans Henrik; "Wilhelm Ludvig Johannsen (1857-1927)"; retrieved from: darwinakive.dk

Stankus, Tony; "Wilhelm Ludvig Johannsen"; in Biographies of Scientists for Sci-Tech Libraries: Adding Faces to Facts; Psychology Press; 1991

Whilhelm Johannsen Wikipedia Entry

August Weismann

Friedrich Leopold August Weismann was born on January 17, 1834 in Frankurt, Germany. His father was a high school teacher and graduate in ancient languages and theology. His early education took place in Frankfurt and at 18 he left to go to the University of Gottingen where he studied medicine, graduating in 1856. After graduation he took a job in the city clinic in Rostock and successfully submitted two papers, one on the synthesis of hippuric acid in herbivores and one on the salt content of the Baltic Sea. He served as the physician of the Archduke of Austria from 1860 to 1862.

He studied zoology at the University of Giessen under Rudolf Leuckart and in 1863 he became privadozent in comparative anatomy at the Albert Ludwig University of Freiburg in Breisgau. He was made extraordinary professor in 1866 and was full professor from 1873 to 1912. He was the first chair in zoology and served as director of the zoological institute. Due to problems with his eyesight there were long periods in which he was unable to do microscope work and his reading and writing was done with the help of others.

Weismann's biological studies led him to theorize that in multicellular organisms there were two type of cells, germ cells and soma cells. Germ cells, such as sperm or ova, are the carriers of biological information, the means by which traits of parent cells were transferred to daughter cells. Somatic cells were the offspring of germ cells and carried out the biological functions of the organism. These somatic cells did not transfer information to future generations. Before the discovery that chromosomes are the means that cells use to transfer genetic information, Weismann's germ cell theory was an important stepping stone, holding that biological traits come from within the organism and do not arise from an external mechanism.

For his work Weismann was awarded the Linnean Society of London's Darwin-Wallace medal in 1908. Weismann died on November 15, 1914.


References:

"August Weisman" in Report of the National Academy of Sciences; U. S. Government Printing Offices; 1914

August Weisman Wikipedia entry

Sir Thomas Lauder Brunton

Sir Thomas Lauder Brunton was born on March 14, 1844 in Bowden, Roxburghshire (in Scotland, near the English border) to James Brunton and his wife Agnes. There are conflicting accounts of his early education, some saying he studied privately and others that he studied at the parish school and then a school at Melrose. He went to Edinburgh University where at his father's urging he began to study law. Taking classes in chemistry and physics in his spare time he soon became so interested in them that he changed his focus. He qualified in 1866, taking the M.B, C.M.Edin. degree with honors and M.D. in 1868 with honors for his thesis on "Digitalis, with some observations on the urine". For a year (1866-67) he served as house physician at the Royal Infirmary, Edinburgh.

After his education he went abroad, intending to visit places mentioned in the story of Joseph from the Bible, visiting Egypt and Syria. He continued his travels visiting Turkey, Greece and Italy. he went to Vienna, where he did laboratory work on digitalis (he never published his results), Berlin, where he analyzed the nuclei of blood cells, Amsterdam and Leipzig where he was one of the first students to be admitted to Carl Ludwig's new institution. It was there that he worked studying arterioles and capillaries making experiments on the effects of amyl nitrate and sodium nitrate. It is the use of amyl nitrate for the relief of angina pectoris that he is chiefly remembered for (drawing on the work of Arthur Gamgee and Benjamin Ward Richardson). Inhaled amyl nitrate causes vasodilation in the coronary arteries and reduced systemic resistance to blood flow.