kaka2za wrote:I wonder how black people ended up in isolated islands of PNG yet there is no history of slave trade in Australia
All Human beings are descended from Africa. Human beings started to migrate from Africa about 70,000 years ago and they migrated in waves.
Those who stayed near the tropics maintained their dark skin tone. Thats why people from Southern India have a dark skin tone as to Papuans, Fijians, Aborigenes and other islanders.
In fact Andamanese skin tone is even darker than those of most native Africans. See the pic below of native Andamanese.

Those who migrated to colder areas started to lose their melanin and lost it over a period of 25,000 years. The colder the area, the less melanin you have. Thats why Scandinavians (like Danes) are much whiter than mediteranneans (like Italians).