In Neolithic times, when agriculture was spreading and was the
number 1 way of getting and accumulating food, people used to eat
the crops they grew or the animals they domesticated. They meat and
crops were the primary products and then they discovered more uses
with the animals. They recieved eggs from chickens and milk froms
cows. These are secondary products and when they found out about
them, it is considered the secondary products revolution.