One person to show that it is possible to co-operate with animals, and train them to follow you around for food; and the rest of people to not murder him for his tasty friends.

Once you have some agriculture; you can have more - spread out into other species of animal and plant - then you settle down. Once you have monoculture you need some kind of trading system between farming groups. When someone gets wise about bartering or inventing a representative currency you start to get civilisation... Or when someone "offers" to pick up a sword so others can keep farming...