I think the rude jam guys owe a lot to breeding and genes. Jamaica's base population were African slaves and they chose the strongest and healthiest men and women, so in an island community you will get the benefits of a trait continuing.
There is a South Pacific island that had a few red headed Scots shipwreck on it about 200 years ago. Today about 80% of the island population has red hair, in a region where almost everyone has black hair.
The shemales seem different, and it is mainly their flacid hang that is so big as most would struggle to get an erection with all of the female hormones they take. If you look at a lot of their "exit points" they are very low which would demonstrate that they are doing a lot of BTC type stretching. This lower exit point would give an extra inch or two in flacid hang, something we all would enjoy. It could be the extended hours tucked between their cheeks that does this over time?