I walk the tracks to work sometimes. ecib and I both walk these tracks, and we are making a stockpile of rail spikes that we find. They wiggle out:
These were invented by Robert Livingston Stevens in 1832. It seems that after 187 years, a simple modification might have been made to keep them from wiggling loose. Maybe a bit of a bump about an inch down from the head?
You might have noticed I made a few little tweaks to the site. I am going to make a few more.
I was in Norway with steve and mike last weekend. It was amazing. We made a small boat and lit it on fire.
You say they wiggle out like that's a bad thing. Any fastener has a failure mode. A spike that gradually wiggles out still has some holding power (mainly needed horizontally) while clearly advertising its weakened condition to a casual inspection. A bump wouldn't increase spike-to-wood contact area much, and could weaken the connection above the bump.
Screws are also used, the cost of pre-boring holes reduced by automated equipment.
Nails haven't evolved much either. I suspect that's because the design and manufacture of wood hasn't changed. I mean, it has - you use different fasteners for glulam - but fundamentally, your other choice is screws.