I'm not sure if you really mean "designed". Some people literally believe that to be true. If that's what you meant, then my useful contribution to the conver

I'm not sure if you really mean "designed". Some people literally believe that to be true. If that's what you meant, then my useful contribution to the conversation will end here :-). If not, and you mean "evolved", then evolution does not necessarily select for a global maximum. It's very likely that instead of "best", you will get "good enough". If it's enough to cause you not to die, then that's fine, generally. Here's an example. If you get some baker's yeast an put it in sugar water and then add a little bit of salt, most of the yeast will not die. However, it will struggle. If you maintain that yeast, in your lifetime it will likely not adapt to the salt, but neither will it grow well. There are yeasts that are adapted to salt, so if they happen to get in there, they will take over. However, if they are not around, the baker's yeast that is struggling there may never adapt to the salt. The mutations that would provide salt adaptation are not guaranteed. It may continue to struggle for aeons. It would be silly to say that it's OK to add salt to the yeast simply because it has lived for a long time in a salty environment. The salt is still bad for it. Just to be clear, just because we evolved in an environment that contains something does not mean that our bodies evolved to handle that problem efficiently. It just wasn't bad enough to kill us off. Similarly (because I see this with diet conversations all the time), the fact that our diet was one way a long time ago, does not in itself suggest that this is a healthy diet. It just means that it wasn't bad enough to kill us off.