In his letter (August AD2000) Brian Dethridge speaks of "the very real tension between evolution and the doctrine of Original Sin".
However, in this context, evolutionary doctrine significantly fails to explain the origin of moral evil in the world; which evil remains exclusive to humans, and is not found in any other mammal. The evolutionary doctrine in question here is Darwinian natural selection acting over time on chance variations to produce evolutionary change. It does not appear to have any relevance to the real existence of moral evil.
On the other hand Original Sin, when understood as a fall from grace on the part of our remote human ancestors, does explain the origin of moral evil in the world and its exclusive presence in the human race. So why the tension between the two doctrines?