Harpo Marx York accent his entire life. According to those who personally knew him, Harpo's voice was much deeper than Groucho's, but it also sounded very similar to Chico's. His son, Bill, recalled that in private Harpo had a very deep and mature soft-spoken voice, but that he was "not verbose" like the other Marx brothers; Harpo preferred listening and learning from others. Harpo's final public appearance came on January 19, 1963 with singer/comedian Allan Sherman. Sherman burst into tears when Harpo announced his retirement from the entertainment business. Comedian Steve Allen, who was in the audience, remembered that Harpo spoke for
Influences on Karl Marx "when Darwin drew the conclusions from his research work and brought them to the knowledge of the public, we spoke of nothing else for months but Darwin and the enormous significance of his scientific discoveries". Historian Richard Weikart points out that Marx had started to attend "a series of lectures by Thomas Henry Huxley on evolution". In August 1866, Marx referred to Pierre Trémaux's "Origine et transformations de l'homme et des autres êtres" (1865) in another letter to Engels as "a very important advance over Darwin". He went further to claim that "in its historical and political application" the book