They both appeared in the same generation; but one didn't cause the other. This is historically obvious, given the timetable I posted earlier. Marx was a published communist theoretician years before Darwin published Origin of the Species. Once both ideas were released into the world, other men read them. Some read one and were influenced, some the other, some both. Some ignored it all. There are probably some professors who even teach both. So what?
It's known that after Darwin became famous, Marx wanted to dedicate some of his later work to him (Das Capital), but I think Darwin paid no attention to Marx. If that's what you're hanging your hat on, it's not very much. Marx had been working on his economic ideas years before evolution was published (like the labor theory of value), and he was probably just trying to add some luster to his work by using Darwin's name.
The timetable is a half-truth which makes it a VERY BIG LIE. Marx's most important work (Das Kapital) was written eight years after the Origins and not finished till 1885. So he had plenty of time to imbibe the waters of evolution.
Publications Books: 1. The Poverty of Philosophy (1847, 1956); 2. Communist Manifesto (1848, 1972); 3. The Class Struggles in France (1848, 1972); 4. A Contribution to the Critique of Political Economy (1859, 1971); 5. Capital , vol 1, (1867, 1976), vols 2 and 3, ed. F. Engels (1885-94, 1909, 1978); 6. Theories of Surplus Value , 3 vols (1905-10, 1963); 7. Collected Works , 12 vols (1927-35); 8. Foundation of the Critique of Political Economy (1939-41, 1973).
From: Marx and Engels .