Evolution works like a tree's structure branches over time. That's why it's always animated like that. It is NOT that everything gets expressed and then gets tested. It is that the current thing "alive" is changing. It seems crazy now only because you're seeing the veeeeerry complicated leaves at the ends of very complicated branches. Branches that have mostly ended by now.

You know what happens to animals with unsurvivable mutations? They die. All the time. Even humans with unsurvivable mutations happen ALL THE TIME.

That's why it's ridiculous to outlaw abortion: Bad things randomly happen all the time, because it's a complicated process with LOTS of areas that can go wrong. It goes wrong all the time. The body has mechanisms to fix a lot of "wrongness", but macro-level bad stuff still happens all the time.

The same thing happens on a species level over many survivable generations.

It IS basically "trial and error", but trial and error in a VERY complicated and dynamic system after a very, very long time, currently stemming from the complicated results of that system.

You cannot dismiss the system just because one aspect confuses you when removed from context...