Informative X thread on how the recurrent laryngeal nerve path is dictated by having to develop embryos through chemotaxis: https://x.com/culpable_mink/status/1850937701518000383

He mentions that even if you're a giraffe, you have nerves just as long running to the end of your spine, and from your spint to the bottoms of your feet, so the extra length of nerve isn't really a problem.

There is a pathway for every possible configuration. It doesn’t dictate whether a configuration is optimal. Maybe the laryngeal nerve isn’t that bad. But that doesn’t guarantee all anatomy and physiology optimal

Not exactly. Everything in our body needs energy to maintain itself. It has to provide some value for the energy it consumes, otherwise not having it becomes an evolutionary advantage meaning evolution will gravitate towards it.

What a_c is getting at is that evolution can become trapped in local optima. The backwards retina in mammals is suboptimal, but it's locally optimal - the path from where we are to a better design (like the one in squid) is too long for evolution to hill-climb up to.

Also, if something truly serves no purpose, evolution will allow it to go away.

The classic example is the enzyme needed to make vitamin C. In our primate ancestors that lived on a diet rich in vitamin C, there was no penalty to losing this enzyme. Mutations that destroyed its function were not selected against. As a result, we now can't make vitamin C; the remnants of the gene for the enzyme have been so damaged that there's no path back to the working version.

Eh evolution will certainly try to fix things that ain't broke, indeed it will try to vary just about everything at some point or another. Bad cable management remains because no one survives the intermediate steps between functional configuration A and optimal configuration Z.