The point being is that an organism doesn't face one problem at a time.
Correct. And the problem address with a GA isn't singular either! Like that network I described - it has multiple problems (functionality, size, cost, weight) and all must be addressed SIMULTANEOUSLY to achieve a good answer. And we're willing to sacrifice in some areas to gain in others, but not too much.
GAs are great as solving "fuzzy, open" solution sets that exist in the real world. Where you can have dozens, thousands, or infinite numbers of solutions but where you just want one that works really well for your own needs.
Again, like mashed potatoes. How much salt is enough? You can't answer that unless you know what I like, how much I want to eat, what else I am having with the potatoes (gravy or sauces), how long the potatoes will linger on my plate (and thus intensify the taste of salt)...
What if the better the potatoes, the slower I eat them as to savor them? How much salt to add at that point? Or knowing that if the beef is dry, I will use more gravy? Or if it's a cold night the food will chill faster and that will decrease the flavor intensity? Am I going to choose a red wine, beer, or simply water with my meal, knowing that alcohol will decrease my sensitivity to salt? Am I going to eat a 6 PM or 10 PM, where physical exhaustion is an issue in terms of salt intake and perception?
Suddenly the amount of salt is dependent not just on the potatoes, but my actions (speed of consumption, gravy, other items consumed), completely external variables (temperature and time of day), and that some of those actions are driven by other items (the dryness of the beef or what I choose to drink with my meal)!
See, it becomes a rather complex problem VERY quickly. THIS is the type of problem you try to solve with a GA.