Grammar aside, there are a number of issues that you should spend some time on here. Just to mention one, but your relating of the electrical signals in the eye implies that this was a wholly human invention; as if we were the ones who invented our eyes. I would suggest removing it, or using it as an example of what nature uses electricity for. You could say something like, far before we knew how to harness electricity, it was already affecting our daily lives.
Besides that, watch those run-on sentences and grammar faux-pax's. Since I suspect this was something you wrote up quickly and have no intention of returning to later, have someone you know proofread your stories in the future. Even a normal text editor like Word or Writely can help a lot. Even firefox will tell you "replys" is spelled wrong.
What is the greatest scientific discovery? The elasticity of human spit.
