Disclaimer: This is solely my own theory, but for me it sounds like the most probable reason for why gold has played such an important store of value through human history in all cultures.

In Nature shiny things are not common, but ripe fruits are very shiny.
The fruit is ripe when it is ready to be eaten (giving humans optimal nutritional value) and for seed dispersal.

It is very plausible that humans were primarily fruit eaters early on. I used to be very sceptical to that claim before, but I know people that live mostly on fruit. I can eat only bananas for days and still have peak performance, and I am a muscular man.
The main point is that ripe fruits played a big part in early human diet, and getting access to fast glucose could be a huge advantage if you lived among sabre tooth tigers. Also, you only need to outrun one person to survive. Still humans crave sugar, and this certainly has an evolutionary reason.

However, seeing ripe fruits can be very tricky in the dense forests.
This has probably lead to the extremely harsh sexual pressure on men over time. The male that was best at finding ripe fruits got the girls.

I remember when I was 20 and got a little bit myopic after reading too many books. It was only like -0.25 D, negligible really, but still enough that my sight was unfocused. These were the days when laser surgery (LASIK) had just come to Norway, and it was still perceived as risky and very expensive ($6000). No ‘rational’ reason to take surgery, but my subconsciousness probably told me that it was a bad move fitness speaking not to take the operation. I got operated.

Kitco

Since gold is ‘ripe’ and shiny too, we also find it very valuable.
Are you good at finding gold (stacker) then you are probably pretty good at finding ripe fruits too. Or at least women perceive you to be? Just indirectly. By having lots of gold you got a secure high position in the male dominance hierarchy which is the main reason why a woman select a man as a sexual partner. The result is the same, having gold nuggets was a token of your ability to find ripe fruits. It increased your fitness.

Fitness is an individual's ability to propagate its genes

This is probably the reason why close to 100% of stackers are men, but most females are wearing the gold items. Women are actually not interested that much in the value of gold per se, but in the signalling of high social status.

Perhaps this is also why poor people gave apples to the teacher, as it was perceived unconsciously as valuable by the teacher, triggering the rule of reciprocity and gave their boys better grades, so they could enhance their fitness. In the US they actually have something called the Golden Apple Award.