From the New York Times (3 May 2010):
In Darwin Family, Evidence of Inbreeding’s Ill Effects
by Nicholas Wade
Charles Darwin, the author of the theory of evolution, may have been right to worry that his children’s health had been affected by the inbreeding in his own family, especially that of his wife, Emma Wedgwood, who was his first cousin.
A calculation based on first-cousin marriages over four generations of the two dynasties suggests that Darwin’s children had a mild degree of inbreeding, measured by the chance of inheriting the same version of a gene from both parents. Possible consequences of inbreeding can be seen in the children’s illnesses and degree of infertility, three researchers report in the current issue of BioScience.
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The Dispersal of Darwin 