You don't need a whole group to choose to switch to agriculture; just one innovator to show that it works better and the others to not burn that person at the stake for doing it. I say agriculture; but it could be as simple as. I try to encourage this plant to grow more by spreading its seeds, Oh look we have lots of food-plant-X now. Or:

1. I feed the birds my spare fish
2. The birds hang around
3. I occasionally eat the birds too.
4. I domesticate the birds.
5. Stable food source = agriculture.

My point (which I am really not showing well) is that the early stages of agriculture are pretty easy to slip into if you have spare thinking space. And after you have them; what you do with your spare time is up to you...