why didn't PNG agriculture spread to Cape York, Australia?

Following on from this thread about no pre western “civilisation” in Australia:

I understand all the arguments about agriculture not taking hold in Australia because of the highly variable climate cycles of drought and flooding. However specifically for eastern cape york, it’s a monsoon climate with highly predictable rainfall. The wet agro crops of the PNG cultures, eg taro, banana, etc seem like they would be ideally suited.

We also have evidence for trade between the Torres Straight islands (where farming was practiced) and Cape York aboriginal tribes. (covered in Guns, Germs and Steel ).

Do we have any any more detailed info about why agriculture never made the leap across from Torres straight farmers? I found Jared Diamond’s explanation far too brief and unconvincing.

The Torres Strait Islands are all part of Australia (the boundary at the northern end of Queensland was drawn right at the New Guinea side of the strait in the 19th century), but culturally the Torres Strait Islanders are closer to the people of New Guinea than to those on the mainland of Queensland. However, as you say, there was regular contact, so agricultural practices could have passed southwards. Perhaps part of the reason is the language boundary: to the north they spoke Papuan languagues, and to the south they spoke Pama-Nyungan languages (which were spoken in most of Australia, apart from the north end of the Northern Territory and Tasmania).

According to these pages, western and central torres straight islands languages are related to northern Australian languages.

http://en.wikipedia.org/wiki/Pama-Nyungan_languages
http://en.wikipedia.org/wiki/Torres_Strait_Island_languages

Anyway, Language alone doesn’t seem to explain this to me, the pattern elsewhere is that agriculturalists with different languages displaced HG cultures because they could feed many more people in the same area. The mystery to me is why the agriculture torres straight cultures never found a foothold in eastern Cape York and then displaced the aboriginal HG culture. We know they visited, so why did they never stay and plant crops there?

The same question can be asked about the macassans in Arnhem land, but there is a big difference between the dry Arnhem land climate and the native macassan’s climate so it’s easy to understand why they failed to start permanent colonies.

I think you misunderstand the nature of northern Australia. Cape York looks like this, and that is not suitable for cultivating either bana or taro.

Cape York and the Top End, for the most part, receive the same rainfall. They both fall within the seasonally dry tropics, which basically means 900-1500mm rain a year, with >85% being concentrated in the summer wet season. That is not suitable for cultivation of banana or taro, which require year round rainfall, basically rainforest climates.

There are areas of Cape York which fall within the true wet tropics, but such areas make up less than 5% of the area, and all are in the extreme South, and that’s a thousand kilometres form the nearest Torrrest Strait island. So knowledge of banana or taro agriculture from NG needed to spread over 1000 km of unsuitable dry savanna before it could be transmitted to people living in an environment where it could be practiced. That just ain’t gonna happen.

In contrast the rice agriculture of the Macassans was, in theory, ideally suited to the seasonally dry tropics of the Top End. I’ll let you read upon the Humpty Doo rice scheme of the 60s to find out why that didn’t work out.

Am I dumb because I don’t know what PNG means (apart from a graphics file format)?

I looked at the other thread, but I didn’t find the explanation.

PNG is the abbreviation for Papua New Guinea, the nation occupying the eastern half of New Guinea and smaller islands to its east. It comes from the two former divisions it was split into, one an Australian territory and one a Australian League of Nations mandate/United Nations trust territory which had formerly been a German colony.

Guns, Germs, and Steel has a remarkably clear and detailed write-up on precisely the question in the OP, which is very much worth reading.