Basically the question was why gold and not silver, platinum, etc., as the desireable metal for commerce/jewelry. The answer lies in golds uniqueish properties, it is rare (not the rarest), it is unique in color (platinum is hard to distinguish from other metals by sight), where gold is confused for other things or to determine its quality a simple bite test will determine its quality, without needing to melt it down (unlike silver colored metals), it's soft enough to be easily formed into jewelry.