perhaps i misdirected the discussion by posting the text of a review/inteview. in the booklet, singer is a lot more nuanced: he quotes marx/engles as suggesting/claiming that they extend darwinian theory (in particular, he quotes engels eulogizing marx: what darwin did for biological evolution marx did for social evolution, or words to that effect). his criticism of marxism ("some marxists", perhaps, is more appropriate), which it is important to note is part of the larger critique of the left's problems with darwinian theory, is of the notion that biological evolution is a negligible force (including in terms of its historical impact) in defining "innate" human nature. i will try to reproduce exact quotes from the text in the next few days.
singer's primary point, as i read it, is this: the left should not accept or fall prey to the rightist interpretation of evolutionary theory, as a) incompatible with co-operative models and traits and b) assuming that the scientific theory implies moral/ethical positions i.e., the is/ought (fact/value) divide.
--ravi