Many of the examples I see for NS are linear and one dimensional:

"Natural selection favored those with better or more photo-sensitive cells because they could detect things that would eat them that those without, or with lesser photo-sensitive cells could and so they copulated and the adaptation was continued. Each successive generation saw better and better photo-sensitive cells until eventually an image was borne."

That's great for simplification, not so much for anything else. Examples tend to focus on one attribute and how it benefits the animal from among the competition. Conversely the competition, because they do not have that attribute, are selected against. Their population dwindles or go extinct.

But organisms are not made of single attributes, but thousands if not more. Given that the underpinning mutations are mostly random and mostly negative. How do you ensure that two attributes simultaneously benefit the animal? What happens if one mutation is positive and the other negative?

For example, a mutation that adds more photoreceptors in the eye, but less hair cell receptors in the ear?