Having read the various theories on this site, I thought I'd throw in my views. Most British surname dictionaries say that it is derived either from a Norman-French Christian name, Germain (which later came to be widely used in England because of the popularity of the Saint by that name) or from describing someone as "the German".If either are true it almost certainly means that the name developed independently in several places because different people in different places could come to be known as the "son of Germain" or "the German", the name sticking to their particular descendants. I.e. we're not all related and also, both explanations could true.(The name in Wales may have a separate derivation in the Welsh language. I've not read any surname book suggest that, which may indicate that the Welsh Jarmans came from England originally)I've noticed in my own research, leaving aside London which is a special case, the name seems to especially appear in hotspots in Wales, Devon, Kent and Suffolk, with scatterings in other parts of southern England.Because there is no single regional focus, this supports the view that it appeared independently in different places.I've also noticed (from the International genealogical Index) that it appears in Norway and the Netherlands and to some extent Germany.These presumably came about independently as well. The suffix "-man" in surnames is common in Germanic speaking countries. The US and certainly the Australian Jarmans probably would have mainly come from the UK.