The wikipedia article Polydactyly in stem-tetrapods has some explanations on how we ended up with 5 fingers and toes.

The gist of it is that tetrapods (four-limbed vertebrate animals) evolved from a fish similar to a lobe-finned fish that had 5 sets of bones in each of its fins that evolved into fingers and toes. Some tetrapods have subsequently lost digits but the basal state was five.

There’s a book, Your Inner Fish by Neil Shubin that’s full of this kind of stuff. Highly recommend.

Ska 'za? Nah brah.

Yeah probably true. I only thought to look it up because I knew active and passive sonar was a thing.

Passive radar?

machining

No idea about your algorithm problems but have you seen the Cutting Edge Engineering Australia channel? It’s so good.