In 1831, Charles Darwin, proposed a theory of evolution occurring by the process of natural selection. This has come to be known as the Theory of Natural Selection. Darwin worked on his theory for 20 years and after learning that Alfred Russel Wallace, another naturalist, had developed similar ideas, the two made a joint announcement of their discovery in 1858. Darwin published 'On the Origin of Species by Means of Natural Selection' in 1859, 28 years after he proposed his theory of natural selection. 
Darwin’s theory of natural selection states that evolutionary change comes through the production of variation in each generation and differential survival of individuals with different combinations of these variable characters. 
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The research stared the project through family interviews, which led them to create family trees for a variety of Afrikaner families. This approach posed obstacles with some of the record keeping, however the information that could not be found in medical/death record was traced back to church records. They traced families with the gene present as far back as possible. When coming to hurdle in traces the family back they consulted a book entitled Die Geslacht Register der Dude Kaapsche Families which traces many Afrikaner families from the early 19th century to their origins in the 17th century. From tracesing the disease back through family trees they discovered that it originated from settlers from Netherlands and France.
They found that approximately 210 affected individuals in more than 50 families (which constitutes 80% of all the Afrikaner patients ascertained during the survey) was found to be ancestrally related through a common progenitor in the 17th century.
From their research they found a link to the first transmission of the Huntington’s Chorea gene among the Afrikaner population. Among the 344 persons who arrived on the Dordrecht at the Cape in 1658 was a man called Willem Schalk v.d. Merwe. His family had its origins in Oud-Beyerland, which is in the vicinity of Rotterdam. In 1668 he married Elsjie Cloeten, daughter of lacob Cloeten who arrived at the Cape with lan van Riebeeck in 1652. Note that both of them