His parents were the priest and later Professor Michael Sars and his wife Maren Cathrine Welhaven. He remained unmarried. He lived until the death of his mother and his brother in the mother. He then moved with his brother and his sister Mally Lammers after Bestum in Aker, where he died.
The father was indeed pastor, but was actually most interested in biology. He had seen to study theology forced to secure his livelihood. In addition to his parish priest profession he went further by his scientific interests. Especially it had done to him, the marine biology. That's why he took over in 1839 a parish in Manger, an archipelago.
1849 Sars came to the cathedral school in Bergen, which he left in 1853 with a very good witness. In the same year he went to Christiania, put the exam in artium and immediately began the study. Here he was supported by his mother's brother Johan Sebastian Welhaven. A year later, his family also came to Christiania because his father had received at the University an extraordinary chair of biology. The family's house soon became a meeting place for writers, artists and academics.
Like his brother, Ossian he thought first of all, to follow in the scientific footsteps of his father, and after passing the intermediate exam, he began to study medicine. But encouraged by Welhaven, he sent in May 1856 a work on a price mission of the university through the Kalmar Union. He won the gold medal with it. Thereafter he devoted himself to history.
In the summers of 1858 and 1859 he was at the expense of the source font Fund in Copenhagen and made copies of files in the Norwegian Danish archive. In 1858 he also began his first major publication on Norway under the union with Denmark, which came out in four volumes from 1858 to 1865. It was the first comprehensive history of Norway under Danish rule. He also followed the ambitions of a newer generation of historians. The previous generation after 1814 with Keyser and Munch had the new Norway directly attached the vordänische time. They had viewed the new freedom as a continuation of the old freedom and interpreted the conflicts of their time than those who have given it in ancient Norway. But with the modernization of the state questions about the continuity of Norwegian history were more pressing.
The new generation of historians, belonged to the next Sars also Ludvig Daae, Michael Birkeland and Oluf Rygh, had in a circle " Det lærde Holland" found together with Paul Botten -Hansen. After 1863, divided the circle, and to Sars and AO Vinje was formed the circle " Døleringen ", which came in sharp contrast to the " Hollænderne " soon, especially with regard to the Scandinavianism and the Union's policies. They gave in 1867 the magazine Vort land (Our Country ) out, a fight sheet against the deepening of the Norwegian-Swedish Union as the " Second Union Committee " she suggested.
1860 to 1874 he was an assistant in the Norwegian National Archives. In 1865 he was back in Copenhagen and copied sources. Now he began systematically to deal with contemporary historiography and philosophy of history. He read the European historians and followed the debates about positivism and other modern trends in the English, French and German literature. In a series of lectures in winter 1870/1871 he brought the positivism in the Norwegian debate, while his brother Ossian at the same time lectured on Darwinism.
With his first band to Norwegian history Sars was known among historians not only in Norway, but also in Denmark, Sweden and Germany. He was then against the resistance of conservative politicians associate professor at the University of Christiania.
1877-1878 he was the magazine Nyt norsk Tidskrift and from 1882 to 1887, the magazine Nyt Tidsskrift which until 1895 was published in a new series in 1892, out. The magazines had to make the target readership acquainted with the new intellectual currents of the time. In 1879 he became involved with Bjørnson on the part of the left in the political conflicts. In the constitutional dispute of 1882 he wrote a treatise Historisk Indledning til reason Loven ( Historical Introduction to the Constitution ). He also wrote a political history of Norway from 1815 to 1905 and lectured until 1911.
With the 1905 occurred independence of Norway, which he had predicted in his works, his version of Norwegian history was the absolutely prevailing doctrine.
The article is mainly based on the Norsk biografisk leksikon.