Sorry,
There is so much hyperdiffusionism that I overreact sometimes. Actually, North America may have been a place where the idea of farming did diffuse. I'll track down the dates of the arrival of the Mesoamerican maize tradition compared to domestication of local plants. My comment in my post was questioning the idea that New Guinea was diffusion.

Here is a quote from a NYT article that African domestication was different:

New York Times D2 July 27, 2004.

Graph
"Earliest dates cereals were grown as crops, as generally agreed by archaeologists. Estimates of even earlier dates for some crops are disputed

Near East (Rye) 11,000 BC; Near East (Wheat) 8,700 B.C.; China (rice) between 7000 and 6500 B.C.; Central America (Maize) 3500 B.C.; sub-Saharan Africa (Pearl Millet) 2000 B.C.
Source Dr. Katharina Neumann, J. W. Goethe University, Frankfurt

African Pastoral: Archaeologists Rewrite History of Farming

July 27, 2004
By BRENDA FOWLER





Archaeologists have long believed that food production
developed worldwide much the way it did in the Near East:
as climate changes made wild grains less available, hunters
and gatherers settled in villages and relatively quickly
domesticated plants and then, over the next few thousand
years, animals.

But recent genetic studies and excavations in Africa
suggest that the patterns of domestication there were
strikingly different. This new research, emerging in the
last few years in academic books and articles, shows that
in Africa, wild cattle were domesticated several thousand
years before plants, and that farming and herding spread
patchily and slowly across the continent.

Why Africans were relatively late to take up farming and
where the domestication of wild grains first happened are
now the subjects of intense research. One theory is that
wild grain was so abundant throughout the continent that
there was no need to settle down to farming. Already the
new discoveries have caused archaeologists to adjust their
thinking about how societies evolved and to realize how
assumptions arose from concepts developed for the Near
East, where most archaeological work has been done.

"African scholars kept expecting to find domestic plants
very early because the model from the Near East was driving
the thinking on Africa," said Dr. Fiona Marshall, an
archaeologist at Washington University in St. Louis who in
a 2002 article in The Journal of World Prehistory was among
the first to recognize that Africa followed a different
paradigm. "It took us a long time to see that we had a
different pattern."
Bernard