"Perhaps sickle-cell anemia evolved before DDT was invented?"
The chemical components of DDT have always been around. Those components couldn't have been invented, only discovered.
The chemical components of DDT have always been around. Those components couldn't have been invented, only discovered.
Those components couldn't have been discovered by early humans--science (specifically chemistry) hadn't been invented. The best those folks could do was adapt.
And adapt they did. Sickle-cell anemia is just one example of the process of evolution--adaptation to changing conditions. There are many more.
By that logic, nothing has been invented since the raw materials have always been around.