The left is highly incompatible with Darwin's ideas. Man is a war maker by nature, our genetics and culture were selected for in the hot crucible of war. Darwin's conclusions support a strong military, right to bear arms for self-defense, and jail for society's rougher edges. The left does not understand Darwin, for if they did they would become conservatives.
"Eugenics" is a catch-all for dumping on an opponent. It is like saying "poison gas" to discredit the findings of chemistry.
Even if every biologist who ever lived were a monster of depravity, evolution would still happen.
Darwin, Marx, and Wagner were leftist.
http://constitutionalistnc.tripod.com/hitler-leftist/id11.html