Laying out the problem of evil: If there is a God, why does my back hurt so much?

Here is a version of the argument from evil. 

(1) Gratuitous evils probably exist
(2) Gratuitous evils are incompatible with the God of theism (omnipotent, omniscient, all-good
(3) Therefore, the God of theism probably does not exist. 

Gratuitous evils are unnecessary and pointless evils. On the face of things, there seems to be a number of those. My back hurting a lot of the time seems on the face of things to be unnecessary. In fact evolutionary biologists explain it as what happens when creatures transitioned from four legs to two legs, and started standing up straight. That put's pressure on a back that was evolved from creatures with four legs who didn't put so much pressure on their backs. 

What is the best way to respond to an AFE that is spelled out in this way?