Many believe that single celled organisms evolved from the sea to live in collectives on land. These collectives are multicellular organisms, like us! Maybe cavemen wouldn't all have access to sea foods and thus sea minerals, but maybe our original cells did?
"An interesting fact to note is that the mineral composition of modern animals, such as ourselves, is similar to that of these ancient organisms, who originated in the sea. Thus, we can deduce that as animals, and life in general, evolved from the sea."